Solar prominences are formed by partially ionized plasma with inter-particle collision frequencies generally warranting magnetohydrodynamic treatment. In this work, we explore the dynamical impacts and observable signatures of two-fluid effects in the parameter regimes when ion-neutral collisions do not fully couple the neutral and charged fluids. We perform 2.5D two-fluid (charges – neutrals) simulations of the Rayleigh-Taylor instability (RTI) at a smoothly changing interface between a solar prominence thread and the corona. The purpose of this study is to deepen our understanding of the RTI and the effects of the partial ionization on the development of RTI using non-linear two-fluid numerical simulations. Our two-fluid model takes into account viscosity, thermal conductivity, and collisional interaction between neutrals and charges: ionization/recombination, energy and momentum transfer, and frictional heating. In this paper I, the sensitivity of the RTI dynamics to the prominence equilibrium configuration, including the impact of the magnetic field strength and shear supporting the prominence thread, and the amount of prominence mass-loading is explored. We show that, at small scales, a realistically smooth prominence-corona interface leads to qualitatively different linear RTI evolution than that expected for a discontinuous interface, while magnetic field shear has the stabilizing effect of reducing the growth rate or eliminating the instability. In the non-linear phase, we observe that in the presence of field shear the development of the instability leads to formation of coherent and interacting 2.5D magnetic structures, which, in turn, can lead to substantial plasma flow across magnetic field lines and associated decoupling of the fluid velocities of charges and neutrals.
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B. Braileanu, V. Lukin, E. Khomenko, et. al.
Mon, 3 Aug 20
-698/58
Comments: N/A
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少数人ssrvqn-outline
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http://arxiv.org/abs/2007.15782
The surface processes on interstellar dust grains have an important role in the chemical evolution in molecular clouds. Hydrogenation reactions on ice surfaces have been extensively investigated and are known to proceed at low temperatures mostly below 20 K. In contrast, information about the chemical processes of molecules within an ice mantle is lacking. In this work, we investigated diffusive hydrogenation reactions of carbon monoxide (CO) embedded in amorphous solid water (ASW) as a model case and discovered that the hydrogenation of CO efficiently proceeds to yield H2CO and CH3OH even above 20 K when CO is buried beneath ASW. The experimental results suggest that hydrogen atoms diffuse through the cracks of ASW and have a sufficient residence time to react with embedded CO. The hydrogenation reactions occurred even at temperatures up to ~70 K. Cracks collapse at elevated temperatures but the occurrence of hydrogenation reactions means that the cracks would not completely disappear and remain large enough for penetration by hydrogen atoms. Considering the hydrogen-atom fluence in the laboratory and molecular clouds, we suggest that the penetration of hydrogen and its reactions within the ice mantle occur in astrophysical environments. Unified Astronomy
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M. Tsuge, H. Hidaka, A. Kouchi, et. al.
Mon, 3 Aug 20
-697/58
Comments: N/A
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少数人ssrvqn-outline
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http://arxiv.org/abs/2007.15914
Relativistic reflection features in the X-ray spectra of black hole binaries and AGNs originate from illumination of the inner part of the accretion disk by a hot corona. In the presence of high quality data and with the correct astrophysical model, X-ray reflection spectroscopy can be quite a powerful tool to probe the strong gravity region, study the morphology of the accreting matter, measure black hole spins, and even test Einstein’s theory of general relativity in the strong field regime. There are a few relativistic reflection models available today and developed by different groups. All these models present some differences and have a number of simplifications introducing systematic uncertainties. The question is whether different models provide different measurements of the properties of black holes and how to arrive at a common model for the whole X-ray astronomy community. In this paper, we start exploring this issue by analyzing a Suzaku observation of the stellar-mass black hole in GRS 1915+105 and simultaneous XMM-Newton and NuSTAR observations of the supermassive black hole in MCG-6-30-15. The relativistic reflection component of these sources is fitted with RELCONV$\times$REFLIONX, RELCONV$\times$XILLVER, and RELXILL. We discuss the differences and the impact on the study of accreting black holes.
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A. Tripathi, H. Liu and C. Bambi
Mon, 3 Aug 20
-696/58
Comments: 15 pages, 9 figures
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少数人ssrvqn-outline
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http://arxiv.org/abs/2007.15667
A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA HI emission-line mapping, optical imaging and numerical simulations of VCC 848, in order to examine the impact of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its HI gas concentrated within the central high-surface-brightness star-forming region, while the remaining HI is entrained in outlying tidal features. Particularly, a well-defined tidal arm reaches N(HI) comparable to the galaxy center but lacks SF. The molecular gas mass inferred from the current SF rate (SFR) dominates over the atomic gas mass in the central ~ 1.5 kpc. VCC 848 is consistent with being a main-sequence star-forming galaxy for its current stellar mass and SFR. The HII region luminosity distribution largely agrees with that of normal dwarf irregulars with similar luminosities, except that the brightest HII region is extraordinarily luminous. Our N-body/hydrodynamical simulations imply that VCC 848 is a merger between a gas-dominated primary progenitor and a gas-bearing star-dominated secondary. The progenitors had their first passage on a near-radial non-coplanar orbit more than 1 Gyr ago. The merger did not build up a core as compact as typical compact dwarfs with centralized starburst, which may be partly ascribed to the star-dominated nature of the secondary, and in a general sense, a negative stellar feedback following intense starbursts triggered at early stages of the merger.
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H. Zhang, R. Smith, S. Oh, et. al.
Mon, 3 Aug 20
-695/58
Comments: 25 pages, 14 figures, accepted by ApJ
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少数人ssrvqn-outline
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http://arxiv.org/abs/2007.15747
Because the same massive stars that reionized the intergalactic medium (IGM) inevitably exploded as supernovae that polluted the Universe with metals, the history of cosmic reionization and enrichment are intimately intertwined. While the overly sensitive Ly-alpha transition completely saturates in a neutral IGM, strong low-ionization metal lines like the MgII 2796,2804 doublet will give rise to a detectable `metal-line forest’ if the metals produced during reionization (Z ~ 10^{-3}Z_sol) permeate the neutral IGM. We simulate the MgII forest for the first time by combining a large hydrodynamical simulation with a semi-numerical reionization topology, assuming a simple enrichment model where the IGM is uniformly suffused with metals. In contrast to the traditional approach of identifying discrete absorbers, we treat the absorption as a continuous random field and measure its two-point correlation function, leveraging techniques from precision cosmology. We show that a realistic mock dataset of 10 JWST spectra can simultaneously determine the Mg abundance, [Mg/H], with a 1sigma precision of 0.02 dex and measure the global neutral fraction <x_HI> to 5% for a Universe with <x_HI> = 0.74 and [Mg/H] = -3.7. Alternatively, if the IGM is pristine, a null-detection of the MgII forest would set a stringent upper limit on the IGM metallicity of [Mg/H] < -4.4 at 95% credibility, assuming <x_HI> > 0.5 from another probe. Concentrations of metals in the circumgalactic environs of galaxies can significantly contaminate the IGM signal, but we demonstrate how these discrete absorbers can be easily identified and masked such that their impact on the correlation function is negligible. The MgII forest thus has tremendous potential to precisely constrain the reionization and enrichment history of the Universe.
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J. Hennawi, F. Davies, F. Wang, et. al.
Mon, 3 Aug 20
-694/58
Comments: 22 pages, 13 figures, submitted to MNRAS
We study the anomalous mass defects in the first (ascendant) branch of stellar sequences of static strange stars. We employ the nonperturbative equation of state derived in the framework of the Field Correlator Method to describe the hydrostatic equilibrium of the strange matter. The large distance static $q{\bar q}$ potential $V_1$ and the gluon condensate $G_2$ are the model parameters that characterize the equation of state. An attempt is made to determine, from the surface gravitational redshift measurements, the ratio $({\cal P}/{\cal E})_C$ at the center of strange stars. For $V_1=0$ and $G_2\gappr0.035\,{\rm GeV}^4$\,, it is shown that $({\cal P}/{\cal E})_C\simeq0.262$ and the corresponding redshift $z_S\simeq0.47$ are limiting values, at the maximum mass of the stellar sequence . As a direct application of our study, we try to determine the values of $V_1$ and $G_2$ from astrophysical observations of the compact star 1E1207.4-5209. Our findings show that $V_1=0.44\pm0.1$\,GeV and $G_2=0.008\pm0.001\,{\rm GeV}^4$\,. As a consequence of these high values of the model parameters, the anomalous mass defect of 1E1207.4-5209 is $|\Delta_2M|\simeq2.6\times10^{53}$\,erg\,.
The innovative Saturn Ring Skimmer mission concept enables a wide range of investigations that address fundamental questions about Saturn and its rings, as well as giant planets and astrophysical disk systems in general. This mission would provide new insights into the dynamical processes that operate in astrophysical disk systems by observing individual particles in Saturn’s rings for the first time. The Ring Skimmer would also constrain the origin, history, and fate of Saturn’s rings by determining their compositional evolution and material transport rates. In addition, the Ring Skimmer would reveal how the rings, magnetosphere, and planet operate as an inter-connected system by making direct measurements of the ring’s atmosphere, Saturn’s inner magnetosphere and the material owing from the rings into the planet. At the same time, this mission would clarify the dynamical processes operating in the planet’s visible atmosphere and deep interior by making extensive high-resolution observations of cloud features and repeated measurements of the planet’s extremely dynamic gravitational field. Given the scientific potential of this basic mission concept, we advocate that it be studied in depth as a potential option for the New Frontiers program.
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M. Tiscareno, M. Vaquero, M. Hedman, et. al.
Mon, 3 Aug 20
-692/58
Context: Chandra observations of the Abell 3411-3412 merging system have revealed an outbound bullet-like sub-cluster in the northern part and many surface brightness (SB) edges at the southern periphery, where multiple diffuse sources are also reported from radio observations. Notably, a south-eastern radio relic associated with fossil plasma from a radio galaxy and with a detected X-ray edge provides direct evidence of shock re-acceleration. The properties of the reported X-ray edges have yet to be constrained from a thermodynamic view. Aims: We use the XMM-Newton and Suzaku observations to reveal the thermodynamical nature of the reported re-acceleration site and other X-ray edges. Meanwhile, we aim to investigate the temperature profile in the low-density outskirts with Suzaku data. Methods: We perform both imaging and spectral analysis to measure the density jump and the temperature jump across multiple known X-ray SB discontinuities. We present a new method to calibrate the XMM-Newton soft proton background. Archival Chandra, Suzaku, and ROSAT data are used to estimate the cosmic X-ray background and Galactic foreground levels with improved accuracy compared to standard blank sky spectra. Results: At the south-eastern edge, both XMM-Newton and Suzaku’s temperature jumps point to a $\mathcal{M}\sim1.2$ shock, which agrees with result from SB fits with Chandra, and supports the re-acceleration scenario at this shock front. The southern edge shows a more complex scenario, where a shock and the presence of stripped cold material may coincide. The Suzaku temperature profiles in the southern low density regions are marginally higher than the typical relaxed cluster temperature profile. The measured value $kT_{500}=4.84\pm0.04\pm0.19$ keV with XMM-Newton and $kT_{500}=5.17\pm0.07\pm0.13$ keV with Suzaku are significantly lower than previously inferred from Chandra.
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X. Zhang, A. Simionescu, H. Akamatsu, et. al.
Mon, 3 Aug 20
-691/58
Comments: 19 pages, 11 figures (+8 in appendix), 7 tables (+3 in appendix). Accepted for publication in A&A
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Seamless maps of major elements of the Moon: Results from high-resolution geostationary satellite [EPA]
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http://arxiv.org/abs/2007.15858
Major elements such as Fe, Ti, Mg, Al, Ca, and Si play very important roles in understanding the origin and evolution of the Moon. Previous maps of these major elements derived from orbital data are based on mosaic images or low-resolution Gamma ray data. The hue variations and gaps among orbital boundaries in the mosaic images are not conducive to geological studies. This paper aims to produce seamless and homogenous distribution maps of major elements using the single-exposure image of the whole lunar disk obtained by China’s high-resolution geostationary satellite, Gaofen-4, with a spatial resolution of ~500 m. The elemental contents of soil samples returned by Apollo and Luna missions were used as ground truth, and were correlated with the reflectance of the sampling sites extracted from Gaofen-4 data. The final distribution maps of these major oxides are generated with the statistical regression model. With these products the average contents and proportions of the major elements for maria and highlands were estimated and compared. The results showed that SiO2 and TiO2 have the highest and lowest fractions in mare and highland areas, respectively. Besides, the relative concentrations of these elements could serve as indicators of geologic processes, e.g., the obviously asymmetric distributions of Al2O3, CaO, and SiO2 around Tycho crater may suggest that Tycho crater was formed by an oblique impact from the southwest direction.
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Y. Lu, Y. Wu, C. Li, et. al.
Mon, 3 Aug 20
-690/58
Comments: N/A
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Force-free magnetosphere attractors for near-horizon extreme and near-extreme limits of Kerr black hole [CL]
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http://arxiv.org/abs/2007.15662
We propose a new approach to find magnetically-dominated force-free magnetospheres around highly spinning black holes, relevant for models of astrophysical jets. Employing the near-horizon extreme Kerr (NHEK) limit of the Kerr black hole, any stationary, axisymmetric and regular force-free magnetosphere reduces to the same attractor solution in the NHEK limit with null electromagnetic field strength. We use this attractor solution as the universal starting point for perturbing away from the NHEK region in the extreme Kerr spacetime. We demonstrate that by going to second order in perturbation theory, it is possible to find magnetically dominated magnetospheres around the extreme Kerr black hole. Furthermore, we consider the near-horizon near-extreme Kerr (near-NHEK) limit that provides access to a different regime of highly spinning black holes. Also in this case we find a novel force-free attractor, which can be used as the universal starting point for a perturbative construction of force-free magnetospheres. Finally, we discuss the relation between the NHEK and near-NHEK attractors.
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F. Camilloni, G. Grignani, T. Harmark, et. al.
Mon, 3 Aug 20
-689/58
Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions have however been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6+564032.5 ($z=1.709$). The hot intracluster gas appears to be fueling a massive burst of star formation ($\approx900$~M$_\odot$yr$^{-1}$) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Intracluster stars are therefore not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities such as clusters and proto-clusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.
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J. Hlavacek-Larrondo, C. Rhea, T. Webb, et. al.
Mon, 3 Aug 20
-688/58
Comments: 7 pages, 4 figures. Accepted for publication in The Astrophysical Journal Letters (see also Chandra press release of August 3rd 2024)
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Constraining the Gravitational Lensing of $z\gtrsim6$ Quasars from their Proximity Zones [GA]
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http://arxiv.org/abs/2007.15657
Since their discovery twenty years ago, the observed luminosity function of $z\gtrsim6$ quasars has been suspected to be biased by gravitational lensing. Apart from the recent discovery of UHS J0439+1634 at $z\approx6.52$, no other strongly lensed $z\gtrsim6$ quasar has been conclusively identified. The hyperluminous $z\approx6.33$ quasar SDSS J0100+2802, believed to host a supermassive black hole of $\sim10^{10} M_\odot$, has recently been claimed to be lensed by a factor of $\sim450$, which would negate both its extreme luminosity and black hole mass. However, its Ly$\alpha$-transparent proximity zone is the largest known at $z>6$, suggesting an intrinsically extreme ionizing luminosity. Here we show that the lensing hypothesis of $z\gtrsim6$ quasars can be quantitatively constrained by their proximity zones. We first show that our proximity zone analysis can recover the strongly lensed nature of UHS J0439+1634, with an estimated magnification $\mu=28.0^{+18.4}{-11.7}(^{+44.9}{-18.3})$ at 68% (95%) credibility that is consistent with previously published lensing models. We then show that the large proximity zone of SDSS J0100+2802 rules out lensing magnifications of $\mu>4.9$ at 95% probability, and conclusively rule out the proposed $\mu>100$ scenario. Future proximity zone analyses of existing $z\gtrsim6$ quasar samples have the potential to identify promising strongly lensed candidates, constrain the distribution of $z\gtrsim6$ quasar lensing, and improve our knowledge of the shape of the intrinsic quasar luminosity function.
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F. Davies, F. Wang, A. Eilers, et. al.
Mon, 3 Aug 20
-687/58
Comments: 8 pages, 4 figures
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Doppler beaming factors for white dwarfs, main sequence stars, and giant stars Limb-darkening coefficients for 3D (DA and DB) white dwarf models [SSA]
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http://arxiv.org/abs/2007.15715
We computed Doppler beaming factors for DA, DB, and DBA white dwarf models, as well as for main sequence and giant stars covering the transmission curves of the Sloan, UBVRI, HiPERCAM, Kepler, TESS, and Gaia photometric systems. The calculations of the limb-darkening coefficients for 3D models were carried out using the least-squares method for these photometric systems. The beaming factor calculations, which use realistic models of stellar atmospheres, show that the black body approximation is not accurate, particularly for the filters $u$, $u’$, $U$, $g$, $g’$, and $B$. The black body approach is only valid for high effective temperatures and/or long effective wavelengths. Therefore, for more accurate analyses of light curves, we recommend the use of the beaming factors presented in this paper. Concerning limb-darkening, the distribution of specific intensities for 3D models indicates that, in general, these models are less bright toward the limb than their 1D counterparts, which implies steeper profiles. To describe these intensities better, we recommend the use of the four-term law (also for 1D models) given the level of precision that is being achieved with Earth-based instruments and space missions such as Kepler and TESS (and PLATO in the future).
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A. Claret, E. Cukanovaite, K. Burdge, et. al.
Mon, 3 Aug 20
-686/58
Comments: Accepted Astronomy&Astrophysics
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Constraining the origin and models of chemical enrichment in galaxy clusters using the Athena X-IFU [GA]
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http://arxiv.org/abs/2007.15910
The chemical enrichment of the Universe at all scales is related to stellar winds and explosive supernovae phenomena. Metals produced by stars and later spread at the mega-parsec scale through the intra-cluster medium (ICM) become a fossil record of the chemical enrichment of the Universe and of the dynamical and feedback mechanisms determining their circulation. As demonstrated by the results of the soft X-ray spectrometer onboard Hitomi, high resolution X-ray spectroscopy is the path to to differentiate among the models that consider different metal production mechanisms, predict the outcoming yields, and are function of the nature, mass, and/or initial metallicity of their stellar progenitor. Transformational results shall be achieved through improvements in the energy resolution and effective area of X-ray observatories to detect rare metals (e.g. Na, Al) and constrain yet uncertain abundances (e.g. C, Ne, Ca, Ni). The X-ray Integral Field Unit (X-IFU) instrument onboard the next-generation European X-ray observatory Athena is expected to deliver such breakthroughs. Starting from 100 ks of synthetic observations of 12 abundance ratios in the ICM of four simulated clusters, we demonstrate that the X-IFU will be capable of recovering the input chemical enrichment models at both low ($z = 0.1$) and high ($z = 1$) redshifts, while statistically excluding more than 99.5% of all the other tested combinations of models. By fixing the enrichment models which provide the best fit to the simulated data, we also show that the X-IFU will constrain the slope of the stellar initial mass function within $\sim$12%. These constraints will be key ingredients in our understanding of the chemical enrichment of the Universe and its evolution.
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F. Mernier, E. Cucchetti, L. Tornatore, et. al.
Mon, 3 Aug 20
-685/58
Comments: 17 pages, 6 figures, accepted for publication in A&A
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Short-term stability of particles in the WD J0914+1914 white dwarf planetary system [EPA]
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http://arxiv.org/abs/2007.16174
Nearly all known white dwarf planetary systems contain detectable rocky debris in the stellar photosphere. A glaring exception is the young and still evolving white dwarf WD J0914+1914, which instead harbours a giant planet and a disc of pure gas. The stability boundaries of this disc and the future prospects for this white dwarf to be polluted with rocks depend upon the mass and orbit of the planet, which are only weakly constrained. Here we combine an ensemble of plausible planet orbits and masses to determine where observers should currently expect to find the outer boundary of the gas disc. We do so by performing a sweep of the entire plausible phase space with short-term numerical integrations. We also demonstrate that particle-star collisional trajectories, which would lead to the (unseen) signature of rocky metal pollution, occupy only a small fraction of the phase space, mostly limited to particle eccentricities above 0.75. Our analysis reveals that a highly inflated planet on a near-circular orbit is the type of planet which is most consistent with the current observations.
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E. Zotos, D. Veras, T. Saeed, et. al.
Mon, 3 Aug 20
-684/58
Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal
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DART Mission Determination of Momentum Transfer: Model of Ejecta Plume Observations [EPA]
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http://arxiv.org/abs/2007.15761
The NASA Double Asteroid Redirection Test (DART) spacecraft will impact the secondary member of the [65803] Didymos binary in order to perform the first demonstration of asteroid deflection by kinetic impact. Determination of the momentum transfer to the target body from the kinetic impact is a primary planetary defense objective, using ground-based telescopic observations of the orbital period change of Didymos and imaging of the DART impact ejecta plume by the LICIACube cubesat, along with modeling and simulation of the DART impact. LICIACube, contributed by the Italian Space Agency, will perform a flyby of Didymos a few minutes after the DART impact, to resolve the ejecta plume spatial structure and to study the temporal evolution. LICIACube ejecta plume images will help determine the vector momentum transfer from the DART impact, by determining or constraining the direction and the magnitude of the momentum carried by ejecta. A model is developed for the impact ejecta plume optical depth, using a point source scaling model of the DART impact. The model is applied to expected LICIACube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. The ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly strength and porosity, thereby allowing inference of these properties to improve the determination of momentum transfer.
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A. Cheng, A. Stickle, E. Fahnestock, et. al.
Mon, 3 Aug 20
-683/58
Comments: 45 pages, 16 figures. Accepted by Icarus
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TARDIS Paper II: Synergistic Density Reconstruction from Lyman-alpha Forest and Spectroscopic Galaxy Surveys with Applications to Protoclusters and the Cosmic Web [CEA]
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http://arxiv.org/abs/2007.15994
In this work we expand upon the Tomographic Absorption Reconstruction and Density Inference Scheme (TARDIS) in order to include multiple tracers while reconstructing matter density fields at Cosmic Noon (z ~ 2-3). In particular, we jointly reconstruct the underlying density field from simulated Lyman-Alpha forest observations at $z\sim 2.5$ and an overlapping galaxy survey. We find that these data are synergistic, with the Lyman Alpha forest providing reconstruction of low density regions and galaxy surveys tracing the density peaks. We find a more accurate power spectra reconstruction going to higher scales when fitting these two data-sets simultaneously than if using either one individually. When applied to cosmic web analysis, we find performing the joint analysis is equivalent to a Lyman Alpha survey with significantly increased sight-line spacing. Since we reconstruct the velocity field and matter field jointly, we demonstrate the ability to evolve the mock observed volume further to z=0, allowing us to create a rigorous definition of “proto-cluster” as regions which will evolve into clusters. We apply our reconstructions to study protocluster structure and evolution, finding for realistic survey parameters we can provide accurate mass estimates of the z \approx 2 structures and their z = 0 fate.
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B. Horowitz, B. Zhang, K. Lee, et. al.
Mon, 3 Aug 20
-682/58
Comments: 16 pages, 12 figures
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http://arxiv.org/abs/2007.15941
A non-parametric reconstruction of the deceleration parameter $q$ is carried out. The observational datasets are so chosen that they are model independent as much as possible. The present acceleration and the epoch at which the cosmic acceleration sets in is quite as expected, but beyond a certain redshift ($z \sim 2$), a negative value of $q$ appears to be in the allowed region. A survey of existing literature is given and compared with the results obtained in the present work.
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P. Mukherjee and N. Banerjee
Mon, 3 Aug 20
-681/58
Comments: 7 pages, 3 sets of figures
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Possible Time Correlation Between Jet Ejection and Mass Accretion for RW Aur A [SSA]
For the active T-Taur star RW Aur A we have performed long-term (~10 yr) monitoring observations of (1) jet imaging in the [Fe II] 1.644-micron emission line using Gemini-NIFS and VLT-SINFONI; (2) optical high-resolution spectroscopy using CFHT-ESPaDOnS; and (3) V-band photometry using the CrAO 1.25-m telescope and AAVSO. The latter two observations confirm the correlation of time variabilities between (A) the Ca II 8542 A and O I 7772 A line profiles associated with magnetospheric accretion, and (B) optical continuum fluxes. The jet images and their proper motions show that four knot ejections occurred at the star over the past ~15 years with an irregular interval of 2-6 years. The time scale and irregularity of these intervals are similar to those of the dimming events seen in the optical photometry data. Our observations show a possible link between remarkable (Delta_V < -1 mag.) photometric rises and jet knot ejections. Observations over another few years may confirm or reject this trend. If confirmed, this would imply that the location of the jet launching region is very close to the star (r <<0.1 au) as predicted by some jet launching models. Such a conclusion would be crucial for understanding disk evolution within a few au of the star, and therefore possible ongoing planet formation at these radii.
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M. Takami, T. Beck, P. Schneider, et. al.
Mon, 3 Aug 20
-680/58
Comments: 14 pages, 5 figures, Accepted by Astrophysical Journal
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Pre-construction estimates of the Cherenkov Telescope Array sensitivity to a dark matter signal from the Galactic centre [HEAP]
Posted on by arxiverbot
http://arxiv.org/abs/2007.16129
We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA’s unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies.
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C. Consortium, A. Acharyya, R. Adam, et. al.
Mon, 3 Aug 20
-679/58
Comments: 68 pages (including references) and 26 figures
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Theoretical Study of Extensive Air Shower Effects in Atmosphere by Simulating the Lateral structure of Several Cosmic Radiations [HEAP]
Extensive air showers (EAS) are a cascade of electromagnetic radiation and ionized particles that produced in the atmosphere through the interaction of a primary cosmic ray with the atom of nucleus in the air producing a huge amount of secondary particles such as X-ray, electrons, neutrons, muons, alpha particles, etc. In this work, EAS effects were demonstrated by estimating the lateral distribution function (LDF) at ultrahigh energies of the various cosmic ray particles. The LDF of charged particles such as electron and positron pair production, gamma and muons particles was simulated at ultrahigh energies 10^16, 10^18 and 10^19 eV. The simulation was carried out using an air shower simulator called AIRES system version 2.6.0. The effect of the primary particles, energies and zenith angle on the LDF of charged particles produced in the EAS was taken into account. Comparison of LDF for charged particles and experimental results gave good agreement for electron and positron pair production and muons particles at 10^19 eV for 0 and 10 zenith angles
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H. Jassim, A. Al-Rubaiee and I. Al-Alawy
Mon, 3 Aug 20
-678/58
Comments: 9 pages, 4 figures, published in Indian journal of public health research and developments
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Moving away from the Near-Horizon Attractor of the Extreme Kerr Force-Free Magnetosphere [CL]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15665
We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is no known exact analytic solution to force free electrodynamics which is stationary, axisymmetric and magnetically-dominated. However, any stationary, axisymmetric and regular force-free magnetosphere in extreme Kerr black hole approaches the same attractor solution in the near-horizon extreme Kerr (NHEK) limit with null electromagnetic field. We show that by moving away from the attractor solution in the NHEK region, one finds magnetically-dominated solutions in the extreme Kerr black hole with finite and negative angular momentum outflow. This result is achieved using a perturbative analysis up to the second order.
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F. Camilloni, G. Grignani, T. Harmark, et. al.
Mon, 3 Aug 20
-677/58
Shock interaction has been argued to play a role in powering a range of optical transients, including supernovae (particularly the superluminous class), classical novae, stellar mergers, tidal disruption events, and fast blue optical transients. These same shocks can accelerate relativistic ions, generating high-energy neutrino and gamma-ray emission via hadronic pion production. The recent discovery of time-correlated optical and gamma-ray emission in classical novae has revealed the important role of radiative shocks in powering these events, enabling an unprecedented view of the properties of ion acceleration, including its efficiency and energy spectrum, under similar physical conditions to shocks in extragalactic transients. Here we introduce a model for connecting the radiated optical fluence of non-relativistic transients to their maximal neutrino and gamma-ray fluence. We apply this technique to a wide range of extragalactic transient classes in order to place limits on their contributions to the cosmological high-energy gamma-ray and neutrino backgrounds. Based on a simple model for diffusive shock acceleration at radiative shocks, calibrated to novae, we demonstrate that several of the most luminous transients can accelerate protons up to energies $E_{\rm max} \gtrsim 10^{16}$ eV, sufficient to contribute to the IceCube astrophysical background. Furthermore, several of the considered sources$-$particularly hydrogen-poor supernovae$-$may serve as “hidden” gamma-ray sources due to the high gamma-ray opacity of their ejecta, evading constraints imposed by the non-blazar Fermi-LAT background. However, adopting an ion acceleration efficiency $\sim$ 0.3-1$\%$ motivated by nova observations, we find that currently known classes of non-relativistic, potentially shock-powered transients contribute at most a few percent of the total IceCube background.
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K. Fang, B. Metzger, I. Vurm, et. al.
Mon, 3 Aug 20
-676/58
Search for event bursts in XMASS-I associated with gravitational-wave events [HEAP]
Posted on by arxiverbot
http://arxiv.org/abs/2007.16046
We performed a search for event bursts in the XMASS-I detector associated with 11 gravitational-wave events detected during LIGO/Virgo’s O1 and O2 periods. Simple and loose cuts were applied to the data collected in the full 832 kg xenon volume around the detection time of each gravitational-wave event. The data were divided into four energy regions ranging from keV to MeV. Without assuming any particular burst models, we looked for event bursts in sliding windows with various time width from 0.02 to 10 s. The search was conducted in a time window between $-$400 and $+$10,000 s from each gravitational-wave event. For the binary neutron star merger GW170817, no significant event burst was observed in the XMASS-I detector and we set 90% confidence level upper limits on neutrino fluence for the sum of all the neutrino flavors via coherent elastic neutrino-nucleus scattering. The obtained upper limit was (1.3-2.1)$\times 10^{11}$ cm$^{-2}$ under the assumption of a Fermi-Dirac spectrum with average neutrino energy of 20 MeV. The neutrino fluence limits for mono-energetic neutrinos in the energy range between 14 and 100 MeV were also calculated. Among the other 10 gravitational wave events detected as the binary black hole mergers, a burst candidate with a global significance of 3.4$\sigma$ was found at 1801.95 s from GW151012. However, no significant deviation from the background in the reconstructed energy and position distributions was found.
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X. Collaboration, K. Abe, K. Hiraide, et. al.
Mon, 3 Aug 20
-675/58
Comments: 7 pages, 9 figures
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Predicting the kinematic evidence of gravitational instability [SSA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15686
Observations with the Atacama Large Millimeter/Submillimeter array (ALMA) have dramatically improved our understanding of the site of exoplanet formation: protoplanetary discs. However, many basic properties of these discs are not well-understood. The most fundamental of these is the total disc mass, which sets the mass budget for planet formation. Discs with sufficiently high masses can excite gravitational instability and drive spiral arms that are detectable with ALMA . Although spirals have been detected in ALMA observations of the dust , their association with gravitational instability, and high disc masses, is far from clear. Here we report a prediction for kinematic evidence of gravitational instability. Using hydrodynamics simulations coupled with radiative transfer calculations, we show that a disc undergoing such instability has clear kinematic signatures in molecular line observations across the entire disc azimuth and radius which are independent of viewing angle. If these signatures are detected, it will provide the clearest evidence for the occurrence of gravitational instability in planet-forming discs, and provide a crucial way to measure disc masses.
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C. Hall, R. Dong, R. Teague, et. al.
Mon, 3 Aug 20
-674/58
Comments: 10 pages, 7 figures
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Opportunities for probing $U(1)_{T3R}$ with light mediators [CL]
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http://arxiv.org/abs/2007.16191
We consider strategies for using new datasets to probe scenarios in which light right-handed SM fermions couple to a new gauge group, $U(1)_{T3R}$. This scenario provides a natural explanation for the light flavor sector scale, and a motivation for sub-GeV dark matter. There is parameter space which is currently allowed, but we find that much of it can be probed with future experiments. In particular, cosmological and astrophysical observations, neutrino experiments and experiments which search for displaced visible decay or invisible decay can all play a role. Still, there is a small region of parameter space which even these upcoming experiments will not be able to probe. This model can explain the observed 2.4-3$\sigma$ excess of events at the COHERENT experiment in the parameter space allowed by current laboratory experiments, but the ongoing/upcoming laboratory experiments will decisively probe this possibility.
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B. Dutta, S. Ghosh and J. Kumar
Mon, 3 Aug 20
-673/58
Comments: 13 pages, 3 figures, 1 table
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The Milky Way's nuclear star cluster: Old, metal-rich, and cuspy [GA]
(abridged) We provide Ks photometry for roughly 39,000 stars and H-band photometry for about 11,000 stars within a field of about 40″x40″, centred on Sgr A*. In addition, we provide Ks photometry of about 3,000 stars in a very deep central field of 10″x10″, centred on Sgr A*. We find that the Ks luminosity function (KLF) is rather homogeneous within the studied field and does not show any significant changes as a function of distance from the central black hole on scales of a few 0.1 pc. By fitting theoretical luminosity functions to the KLF, we derive the star formation history of the nuclear star cluster. We find that about 80% of the original star formation took place 10 Gyr ago or longer, followed by a largely quiescent phase that lasted for more than 5 Gyr. We clearly detect the presence of intermediate-age stars of about 3 Gyr in age. This event makes up about 15% of the originally formed stellar mass of the cluster. A few percent of the stellar mass formed in the past few 100 Myr. Our results appear to be inconsistent with a quasi-continuous star formation history. The stellar density increases exponentially towards Sgr A* at all magnitudes between Ks=15 to 19. We also show that the precise properties of the stellar cusp around Sgr A* are hard to determine because the star formation history suggests that the star counts can be significantly contaminated, at all magnitudes, by stars that are too young to be dynamically relaxed. We find that the probability of observing any young (non-millisecond) pulsar in a tight orbit around Sgr A* and beamed towards Earth is very low. We argue that typical globular clusters, such as they are observed in and around the Milky Way today, have probably not contributed to the nuclear cluster’s mass in any significant way. The nuclear cluster may have formed following major merger events in the early history of the Milky Way.
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R. Schödel, F. Nogueras-Lara, E. Gallego-Cano, et. al.
Mon, 3 Aug 20
-672/58
Patterns of galaxy spin directions in SDSS and Pan-STARRS show parity violation and multipoles [CEA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.16116
The distribution of spin directions of $\sim6.4\cdot10^4$ SDSS spiral galaxies with spectra was examined, and compared to the distribution of $\sim3.3\cdot10^4$ Pan-STARRS galaxies. The analysis shows a statistically significant asymmetry between the number of SDSS galaxies with opposite spin directions, and the magnitude and direction of the asymmetry changes with the direction of observation and with the redshift. The redshift dependence shows that the distribution of the spin direction of SDSS galaxies becomes more asymmetric as the redshift gets higher. Fitting the distribution of the galaxy spin directions to a quadrupole alignment provides fitness with statistical significance >5$\sigma$, which grows to >8$\sigma$ when just galaxies with z>0.15 are used. Similar analysis with Pan-STARRS galaxies provides dipole and quadrupole alignments nearly identical to the analysis of SDSS galaxies, showing that the source of the asymmetry is not necessarily a certain unknown flaw in a specific telescope system. While these observations are clearly provocative, there is no known error that could exhibit itself in such form. The data analysis process is fully automatic, and uses deterministic and symmetric algorithms with defined rules. It does not involve either manual analysis that can lead to human perceptual bias, or machine learning that can capture human biases or other subtle differences that are difficult to identify due to the complex nature of machine learning processes. Also, an error in the galaxy annotation process is expected to show consistent bias in all parts of the sky, rather than change with the direction of observation to form a clear and definable pattern.
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L. Shamir
Mon, 3 Aug 20
-671/58
Comments: ApSS, accepted. arXiv admin note: substantial text overlap with arXiv:1912.05429
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MHD accretion-ejection: jets launched by a non-isotropic accretion disk dynamo. I. Validation and application of selected dynamo tensorial components [HEAP]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15701
Astrophysical jets are launched from strongly magnetized systems that host an accretion disk surrounding a central object. The origin of the jet launching magnetic field is one of the open questions for modeling the accretion-ejection process. Here we address the question how to generate the accretion disk magnetization and field structure required for jet launching. Applying the PLUTO code, we present the first resistive MHD simulations of jet launching including a non-scalar accretion disk mean-field $\alpha^2\Omega$-dynamo in the context of large scale disk-jet simulations. Essentially, we find the $\alpha_\phi$-dynamo component determining the amplification of the poloidal magnetic field, which is strictly related to the disk magnetization (and, as a consequence, to the jet speed, mass and collimation), while the $\alpha_R$ and $\alpha_\theta$-dynamo components trigger the formation of multiple, anti-aligned magnetic loops in the disk, with strong consequences on the stability and dynamics of the disk-jet system. In particular, such loops trigger the formation of dynamo inefficient zones, which are characterized by a weak magnetic field, and therefore a lower value of the magnetic diffusivity. The jet mass, speed and collimation are strongly affected by the formation of the dynamo inefficient zones. Moreover, the $\theta$-component of the $\alpha$-dynamo plays a key role when interacting with a non-radial component of the seed magnetic field. We also present correlations between the strength of the disk toy dynamo coefficients and the dynamical parameters of the jet that is launched.
Heterodyne Broadband Detection of Axion Dark Matter [CL]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15656
We propose a new broadband search strategy for ultralight axion dark matter that interacts with electromagnetism. An oscillating axion field induces transitions between two quasi-degenerate resonant modes of a superconducting cavity. In two broadband runs optimized for high and low masses, this setup can probe unexplored parameter space for axion-like particles covering fifteen orders of magnitude in mass, including astrophysically long-ranged fuzzy dark matter.
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A. Berlin, R. D’Agnolo, S. Ellis, et. al.
Mon, 3 Aug 20
-669/58
Comments: 10+14 pages, 3 figures
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Posted on by arxiverbot
http://arxiv.org/abs/2007.15676
We aim at carrying out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy by a multi-transitions analysis of the spatial distribution of the 12^CO emission at different spatial scales using HIFI, PACS, SPIRE as well as APEX data. We combined the 12^CO/IR flux ratios and the LTE analysis of the 12^CO images to derive the thermal structure of the Interstellar Medium (ISM) for spatial scales raging from <200 pc to 2 kpc. From the 12^CO analysis we found clear trend in the distribution of the derived temperatures and the 12^CO/IR ratios. It is remarkable that at intermediate scales (360 pc-1 kpc) we see large temperatures in the direction of the X-ray outflow while at smaller scales (<200 pc-360 pc), the highest temperature, derived from the high-J lines, is not found toward the nucleus, but toward the galaxy plane. The thermal structure derived from the 12CO multi-transition analysis suggests that mechanical heating, like shocks or turbulence, dominates the heating of the ISM in the nucleus of NGC 4945 located beyond 100 pc from the center of the galaxy. This result is further supported by the Kazandjian et al. 2015 models, which are able to reproduce the emission observed at high-J (PACS) 12^CO transitions when mechanical heating mechanisms are included. Shocks and/or turbulence are likely produced by the barred potential and the outflow, observed in X-rays.
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E. Bellocchi, J. Martín-Pintado, R. Güsten, et. al.
Mon, 3 Aug 20
-668/58
The Search for Failed Supernovae with the Large Binocular Telescope: N6946-BH1, Still No Star [SSA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15658
We present new Large Binocular Telescope, Hubble Space Telescope, and Spitzer Space Telescope data for the failed supernova candidate N6946-BH1. We also report an unsuccessful attempt to detect the candidate with Chandra. The ~300,000 Lsun red supergiant progenitor underwent an outburst in 2009 and has since disappeared in the optical. In the LBT data from May 2008 through October 2024, the upper limit on any increase in the R-band luminosity of the source is 2000 Lsun. HST and Spitzer observations show that the source continued to fade in the near-IR and mid-IR, fading by approximately a factor of 2 between October 2015 and September 2017 to 2900 Lsun at H band (F160W). Models of the spectral energy distribution are inconsistent with a surviving star obscured either by an ongoing wind or dust formed in the transient. The disappearance of N6946-BH1 remains consistent with a failed supernova.
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C. Basinger, C. Kochanek, S. Adams, et. al.
Mon, 3 Aug 20
-667/58
Comments: 9 pages, 7 figures, 2 tables
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Reaching thermal noise at ultra-low radio frequencies: the Toothbrush radio relic downstream of the shock front [HEAP]
Posted on by arxiverbot
http://arxiv.org/abs/2007.16043
Ultra-low frequency observations (<100 MHz) are particularly challenging because they are usually performed in a low signal-to-noise ratio regime due to the high sky temperature and because of ionospheric disturbances whose effects are inversely proportional to the observing frequency. Nonetheless, these observations are crucial to study the emission from low-energy populations of cosmic rays. We aim to obtain the first thermal-noise limited (~ 1.5 mJy/beam) deep continuum radio map using the LOFAR Low Band Antenna (LBA) system. Our demonstration observation targeted the galaxy cluster RX J0603.3+4214 (the “Toothbrush” cluster). We used the resulting ultra-low frequency (58 MHz) image to study cosmic-ray acceleration and evolution in the post shock region, as well as their relation with the presence of a radio halo. We describe the data reduction we have used to calibrate LOFAR LBA observations. The resulting image is combined with observations at higher frequencies (LOFAR 150 MHz and VLA 1500 MHz) to extract spectral information. We obtained the first thermal-noise limited image from an observation carried out with the LOFAR LBA system using all Dutch stations at a central frequency of 58 MHz. With 8 hours of data, we reached an rms noise of 1.3 mJy/beam at a resolution of 18″ x 11″. The procedure we have developed is an important step forward towards routine high-fidelity imaging with the LOFAR LBA. The analysis of the radio spectra shows that the radio relic extends to distances of 800 kpc downstream from the shock front, larger than what allowed by electron cooling time. Furthermore, the shock wave started accelerating electrons already at a projected distance of <300 kpc from the crossing point of the two clusters. These results can be explained if electrons are reaccelerated downstream by background turbulence possibly combined with projection effects.
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F. Gasperin, G. Brunetti, M. Bruggen, et. al.
Mon, 3 Aug 20
-666/58
Recently, the XENON1T collaboration reported an excess in the electron recoil energy spectrum. One of the simplest new physics interpretation is a new neutrino-electron interaction mediated by a light vector particle. However, for the parameter region favored by this excess, the constraints from the stellar cooling are severe. Still, there are astrophysical uncertainties on those constraints. In this paper, we discuss the constraint on the light mediator from the effective number of neutrino Neff in the CMB era, which provides an independent constraint. We show that Neff is significantly enhanced and exceeds the current constraint in the parameter region favored for the XENON1T excess. As a result, the interpretation by a light mediator heavier than about 1 eV is excluded by the Neff constraint.
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M. Ibe, S. Kobayashi, Y. Nakayama, et. al.
Mon, 3 Aug 20
-665/58
Comments: 16 pages, 16 figures
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Temporal evolution of short-lived penumbral microjets [SSA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15926
Context. Penumbral microjets are elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes and are thought to originate from magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only. Aims. Here we investigate the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes $<$ 2 minutes) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere. Methods. We use fast-cadence spectropolarimetric observations of the Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter at the Swedish 1-m Solar Telescope. The weak-field approximation (WFA) is used to estimate the strength and inclination of the magnetic field vector. Results. The WFA reveals larger magnetic field changes in the upper photosphere than in the chromosphere during the PMJ maximum brightness stage. In the photosphere, the magnetic field inclination and strength undergo a transient increase for most PMJs, but in 25$\%$ of the cases the field strength decreases during the brightening. In the chromosphere, the magnetic field tends to be slightly stronger during the PMJs. Conclusions. The propagation of compressive perturbation fronts followed by a rarefaction phase in the aftershock region may explain the observed behavior of the magnetic field vector. The fact that such behavior varies among the analyzed PMJs could be a consequence of the limited temporal resolution of the observations and the fast-evolving nature of the PMJs.
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A. Siu-Tapia, L. Rubio, D. Suárez, et. al.
Mon, 3 Aug 20
-664/58
X-ray evolution of the nova V959 Mon suggests a delayed ejection and a non-radiative shock [HEAP]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15702
X-ray observations of shocked gas in novae can provide a useful probe of the dynamics of the ejecta. Here we report on X-ray observations of the nova V959 Mon, which was also detected in GeV gamma-rays with the Fermi satellite. We find that the X-ray spectra are consistent with a two-temperature plasma model with non-solar abundances. We interpret the X-rays as due to shock interaction between the slow equatorial torus and the fast polar outflow that were inferred from radio observations of V959 Mon. We further propose that the hotter component, responsible for most of the flux, is from the reverse shock driven into the fast outflow. We find a systematic drop in the column density of the absorber between Days 60 and 140, consistent with the expectations for such a picture. We present intriguing evidence for a delay of around 40 days in the expulsion of the ejecta from the central binary. Moreover, we infer a relatively small (a few times 10$^{-6}$ Msun) ejecta mass ahead of the shock, considerably lower than the mass of 10$^4$ K gas inferred from radio observations. Finally, we infer that the dominant X-ray shock was likely not radiative at the time of our observations, and that the shock power was considerably higher than the observed X-ray luminosity. It is unclear why high X-ray luminosity, closer to the inferred shock power, is never seen in novae at early times, when the shock is expected to have high enough density to be radiative.
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T. Nelson, K. Mukai, L. Chomiuk, et. al.
Mon, 3 Aug 20
-663/58
Comments: 17 pages, 7 figures; submitted to Monthly Notices of the Royal Astronomical Society
The close relationship between the nature of the Triangulum-Andromeda (TriAnd) overdensity and the Galactic disk has become increasingly evident in recent years. However, the chemical pattern of this overdensity (R$_{GC}$ = 20 – 30 kpc) is unique and differs from what we know of the local disk. In this study, we analyze the chemical abundances of five $\alpha$ elements (Mg, O, Si, Ca, and Ti) in a sample of stars belonging to the TriAnd overdensity, including stars with [Fe/H] $<$ $-$1.2, to investigate the evolution of the $\alpha$ elements with metallicity. High-resolution spectra from Gemini North with GRACES were analyzed. Overall, the TriAnd population presents an $\alpha$-element pattern that differs from that of the local disk; the TriAnd stars fall in between the local disk and the dwarf galaxies in the [X/Fe] vs. [Fe/H] plane. The high [Mg/Fe] ratios obtained for the lower metallicity TriAnd stars may indicate a roughly parallel sequence to the Milky Way local disk at lower values of [Fe/H], revealing a ‘knee’ shifted towards lower metallicities for the TriAnd population. Similar behavior is also exhibited in the [Ca/Fe] and [Si/Fe] ratios. However, for O and Ti the behavior of the [X/Fe] ratios shows a slight decay with decreasing metallicity. Our results reinforce the TriAnd overdensity as a unique stellar population of the Milky Way, with an abundance pattern that is different from all stellar populations studied to date. The complete understanding of the complex TriAnd population will require high-resolution spectroscopic observations of a larger sample of TriAnd stars.
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J. Silva, K. Cunha, H. Perottoni, et. al.
Mon, 3 Aug 20
-662/58
Comments: N/A
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LOUPE: Observing Earth from the Moon to prepare for detecting life on Earth-like exoplanets [IMA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.16078
LOUPE, the Lunar Observatory for Unresolved Polarimetry of the Earth, is a small, robust spectro-polarimeter with a mission to observe the Earth as an exoplanet. Detecting Earth-like planets in stellar habitable zones is one of the key challenges of modern exoplanetary science. Characterising such planets and searching for traces of life requires the direct detection of their signals. LOUPE provides unique spectral flux and polarisation data of sunlight reflected by the Earth, the only planet known to harbor life. This data will be used to test numerical codes to predict signals of Earth-like exoplanets, to test algorithms that retrieve planet properties, and to fine-tune the design and observational strategies of future space observatories. From the Moon, LOUPE will continuously see the entire Earth, enabling it to monitor the signal changes due to the planet’s daily rotation, weather patterns, and seasons, across all phase angles. Here, we present both the science case and the technology behind LOUPE’s instrumental and mission design.
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D. Klindžić, D. Stam, F. Snik, et. al.
Mon, 3 Aug 20
-661/58
Comments: 13 pages, 5 figures. Accepted for publication in Royal Society Philosophical Transactions A
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Gamma Rays from UltraCompact Minihaloes: Effects on the Earth's Atmosphere and Links to Mass Extinction Events [HEAP]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15975
Recent studies of the effects on the Earth’s atmosphere by astrophysical sources, such as nearby gamma-ray bursts or supernovae, have shown that these events could lead to severe changes in atmospheric composition. Depletion of ozone, the most notable of these changes, is extremely dangerous to living organisms as any decrease in ozone levels leads to an increase in the irradiance of harmful solar radiation at the Earth’s surface. In this work we consider dark matter as an astrophysical source of gamma rays, by the annihilation and decay of WIMPs found within dark compact halo objects known as UltraCompact Minihaloes (UCMHs). We calculate the fluence of gamma rays produced in this way and simulate the resulting changes to terrestrial ozone levels using the Goddard Space Flight Center 2D Atmospheric Model. We also calculate the rate at which such events would occur, using estimates for the mass distribution of these haloes within the Milky Way. We find that the ozone depletion from UCMHs can be significant, and even of similar magnitude to the levels which have been linked to the cause of the Late-Ordovician mass extinction event. However, the probability of such encounters over the Earth’s entire history is relatively low. This suggests that, while dark compact objects like UCMHs could have had an impact on the Earth’s biosphere, other astrophysical phenomena like gamma-ray bursts or supernovae seem a more likely source of these effects.
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M. Sarkis, G. Beck and B. Thomas
Mon, 3 Aug 20
-660/58
Comments: 11 pages, 6 figures, submitted to MNRAS
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Posted on by arxiverbot
http://arxiv.org/abs/2007.15979
Planets are common objects in the Universe, observationally as well as theoretically. However, the standard theory of their formation encounters many difficulties, such as dust fall and disk lifetime problems. We positively analyze them, expecting that those problems as a whole may indicate some consistent effective model. Thus we propose a dynamical model of the planet formation based on the assumption that the inner void of gas is commonly formed in the disk without specifying any Physical origin. The basic processes of this model are the dust fall, the accumulation, and the slingshots. The dust in the protoplanetary disk rapidly falls as it grows to the meter size. Then, all of them stops at the outer edge of the void where the gas friction disappears. Such dust clusters rapidly coalesce with each other and easily cause the runaway in the dense and coherent environment. Then the huge clusters are formed there and they are the first generation planets Hot-Jupiters. They immediately slingshot smaller clusters around them towards the outer regions. They are Rockey-Planets, Cold-Gas-Giants, Ice-Giants, and Trans Neptunian objects includingKuiper belt/Oort cloud objects`, depending on the original core mass or the distance blown. Combining numerical calculations of the slingshots and coagulation equations, we obtain the planet population diagram, including the possibility of the massive thermal metamorphosis, the origin of the variety of planetary systems, and the possibility of stray planets/objects.
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M. Morikawa and S. Amaya
Mon, 3 Aug 20
-659/58
Comments: 16 pages, 10 figures
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Physics in Precision-Dependent Normal Neighborhoods [CL]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15717
We introduce a procedure to determine the size and shape of normal neighborhoods in any spacetimes and their dependence on the precision of the measurements performed by arbitrary observers. As an example, we consider the Schwarzschild geometry in Riemann and Fermi normal coordinates and determine the size and shape of normal neighborhoods in the vicinity of the event horizon. Depending on the observers, normal neighborhoods extend to the event horizon and even beyond into the black hole interior. It is shown that the causal structure supported by normal neighborhoods across an event horizon is consistent with general relativity. In particular, normal neighborhoods reaching over an event horizon are void of the Schwarzschild coordinate singularity. In addition, we introduce a new variant of normal coordinates which we call Fermi normal coordinates around a point, unifying features of Riemann and Fermi normal coordinates, and analyze their neighborhoods.
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B. Hoegl, S. Hofmann and M. Koegler
Mon, 3 Aug 20
-658/58
Comments: 21 pages, 4 figures
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Towards a more rigorous treatment of uncertainties on the velocity distribution of dark matter particles for capture in stars [CEA]
Posted on by 伕理http
http://arxiv.org/abs/2007.15927
Dark matter (DM) capture in stars offers a rich phenomenology that makes it possible to probe a wide variety of particle DM scenarios in diverse astrophysical environments. In spite of decades of improvements to refine predictions of capture-related observables and better quantify astrophysical and particle-physics uncertainties, the actual impact of the Galactic phase-space distribution function of DM has been overlooked. In this work, we tackle this problem by making use of self-consistent equilibrium phase-space models based on the Eddington inversion formalism and an extension of this method to a DM halo with some degree of anisotropy in velocity space. We demonstrate that incorrectly accounting for the variation of the DM velocity distribution with position in the Galaxy leads to a systematic error between a factor two and two orders of magnitude, depending in particular on the target star, the DM candidate mass and the type of interaction involved. Moreover, we show that underlying phase-space properties, such as the anisotropy of the velocity tensor, actually play an important part—previously disregarded—and can have a sizable impact on predictions of capture rates and subsequent observables. We argue that Eddington-like methods, which self-consistently account for kinematic constraints on the components of the Galaxy, actually provide a reliable next-to-minimal approach to narrow down uncertainties from phase-space modeling on predictions of observables related to DM capture in stars.
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J. Lopes, T. Lacroix and I. Lopes
Mon, 3 Aug 20
-657/58
Comments: 38 pages, 7 figures
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http://arxiv.org/abs/2007.15708
The aim of the present work is to study structure and gas kinematics in the photodissociation regions (PDRs) around the compact HII regions S235A and S235C. We observe the [CII], [13CII] and [OI] line emission, using SOFIA/upGREAT and complement them by data of HCO+ and CO. We use the [13CII] line to measure the optical depth of the [CII] emission, and find that the [CII] line profiles are influenced by self-absorption, while the [13CII] line remains unaffected by these effects. Hence, for dense PDRs, [13CII] emission is a better tracer of gas kinematics. The optical depth of the [CII] line is up to 10 in S235A. We find an expanding motion of the [CII]-emitting layer of the PDRs into the front molecular layer in both regions. Comparison of the gas and dust columns shows that gas components visible neither in the [CII] nor in low-J CO lines may contribute to the total column across S235A. We test whether the observed properties of the PDRs match the predictions of spherical models of expanding HII region + PDR + molecular cloud. Integrated intensities of the [13CII], [CII] and [OI] lines are well-represented by the model, but the models do not reproduce the double-peaked [CII] line profiles due to an insufficient column density of C+. The model predicts that the [OI] line could be a more reliable tracer of gas kinematics, but the foreground self-absorbing material does not allow using it in the considered regions.
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M. Kirsanova, V. Ossenkopf-Okada, L. Anderson, et. al.
Mon, 3 Aug 20
-656/58
We consider a disformal coupling between Standard Model matter and a cubic Galileon scalar sector, assumed to be a relict of some other physics that solves the cosmological constant problem rather than a solution in its own right. This allows the energy density carried by the Galileon scalar to be sufficiently small that it evades stringent constraints from the integrated Sachs-Wolfe effect, which otherwise rules out the cubic Galileon theory. Although the model with disformal coupling does not exhibit screening, we show there is a `screening-like’ phenomenon in which the energy density carried by the Galileon scalar is suppressed during matter domination when the quadratic and cubic Galileon operators are both relevant and the quadratic sector has a stable kinetic term. We obtain the explicit 3+1 form of Maxwell’s equations in the presence of the disformal coupling, and the wave equations that govern electromagnetic waves. The disformal coupling is known to generate a small mass that modifies their velocity of propagation. We use the WKB approximation to study electromagnetic waves in this theory and show that, despite remarkable recent constraints from the LIGO/Virgo observatories that restrict the difference in propagation velocity between electromagnetic and gravitational radiation to roughly 1 part in $10^{15}$, the disformal coupling is too weak to be constrained by events such as GW170817 or by the dispersion of electromagnetic radiation at different wavelengths.
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M. Lawrence, D. Seery and C. Byrnes
Mon, 3 Aug 20
-655/58
Comments: 18 pages, 1 figure
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http://arxiv.org/abs/2007.15967
Protoplanetary discs are made of gas and dust orbiting a young star. They are also the birth place of planetary systems, which motivates a large amount of observational and theoretical research. In these lecture notes, I present a review of the magnetic mechanisms applied to the outer regions R>1 AU of these discs, which are the planet-formation regions. In contrast to usual astrophysical plasmas, the gas in these regions is noticeably cold (T<300 K) and dense, which implies a very low ionisation fraction close to the disc midplane. In these notes, I deliberately ignore the innermost R~0.1 AU region which is influenced by the star-disk interaction and various radiative effects. I start by presenting a short overview of the observational evidence for the dynamics of these objects. I then introduce the methods and approximations used to model these plasmas, including non-ideal MHD, and the uncertainties associated with this approach. In this framework, I explain how the global dynamics of these discs is modelled, and I present a stability analysis of this plasma in the local approximation, introducing the non-ideal magneto-rotational instability. Following this mostly analytical part, I discuss numerical models which have been used to describe the saturation mechanisms of this instability, and the formation of large-scale structures by various saturation mechanisms. Finally, I show that local numerical models are insufficient since magnetised winds are also emitted from the surface of these objects. After a short introduction on winds physics, I present global models of protoplanetary discs, including both a large-scale wind and the non-ideal dynamics of the disc.
Machine learning (ML) methods can expand our ability to construct, and draw insight from large datasets. Despite the increasing volume of planetary observations, our field has seen few applications of ML in comparison to other sciences. To support these methods, we propose ten recommendations for bolstering a data-rich future in planetary science.
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A. Azari, J. Biersteker, R. Dewey, et. al.
Fri, 31 Jul 20
-643/69
Comments: 10 pages (expanded citations compared to 8 page submitted version for decadal survey), 3 figures, white paper submitted to the Planetary Science and Astrobiology Decadal Survey 2024-2032
We present the Sejong Suite, an extensive collection of state-of-the-art high-resolution cosmological hydrodynamical simulations spanning a variety of cosmological and astrophysical parameters, primarily developed for modeling the Lyman-Alpha (LyA) forest. The suite is organized into three main categories (Grid Suite, Supporting Suite, and Systematics Suite), addressing different science targets. Adopting a particle-based implementation, we follow the evolution of gas, dark matter (cold and warm), massive neutrinos, and dark radiation, and consider several combinations of box sizes and number of particles. With additional enhancing techniques, we are able to reach an equivalent resolution up to 3×3328^3=110 billion particles in a (100 Mpc/h)^3 box size, ideal for current and future surveys (e.g., eBOSS, DESI). Noticeably, for the first time, we simulate extended mixed scenarios describing the combined effects of warm dark matter, neutrinos, and dark radiation, modeled consistently by taking into account the neutrino mass splitting. In addition to providing multicomponent snapshots from z=5.0 to z=2.0 in intervals of dz=0.2 for all of the models considered, we produced over 288 million LyA skewers in the same z-range and extended parameter space. The skewers are well suited for LyA forest science studies, for mapping the high-$z$ cosmic web and the matter-to-flux relation and bias, and for quantifying the critical role of baryons at small scales. We also present a first analysis of the suite focused on the matter and flux statistics, and show that we are able to accurately reproduce the 1D flux power spectrum down to scales k=0.06 [s/km] as mapped by recent high-resolution quasar data, as well as the thermal history of the intergalactic medium. The simulations and products described here will be progressively made available.
Maximally self-interacting dark matter: models and predictions [CL]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15522
We study self-interacting dark matter (SIDM) scenarios, where the $s$-wave self-scattering cross section almost saturates the Unitarity bound. Such self-scattering cross sections are featured by strong velocity dependence in a wide range of velocities. They may be indicated by observations of dark matter halos in a wide range of masses, from Milky Way’s dwarf spheroidal galaxies to galaxy clusters. We pin down the model parameters that saturates the Unitarity bound in well-motivated SIDM models: the gauged $L_{\mu} – L_{\tau}$ model and composite asymmetric dark matter model. We discuss implications and predictions of such model parameters for cosmology like the $H_{0}$ tension and dark-matter direct-detection experiments, and particle phenomenology like the beam-dump experiments.
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A. Kamada, H. Kim and T. Kuwahara
Fri, 31 Jul 20
-641/69
Comments: 46 pages, 13 figures
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Dark matters on the scale of galaxies [CEA]
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http://arxiv.org/abs/2007.15539
The cold dark matter model successfully explains both the emergence and evolution of cosmic structures on large scales and, when we include a cosmological constant, the properties of the homogeneous and isotropic Universe. However, the cold dark matter model faces persistent challenges on the scales of galaxies. {Indeed,} N-body simulations predict some galaxy properties that are at odds with the observations. These discrepancies are primarily related to the dark matter distribution in the innermost regions of the halos of galaxies and to the dynamical properties of dwarf galaxies. They may have three different origins: (1) the baryonic physics affecting galaxy formation is still poorly understood and it is thus not properly included in the model; (2) the actual properties of dark matter differs from those of the conventional cold dark matter; (3) the theory of gravity departs from General Relativity. Solving these discrepancies is a rapidly evolving research field. We illustrate some of the solutions proposed} within the cold dark matter model, and solutions when including warm dark matter, self-interacting dark matter, axion-like particles, or fuzzy dark matter. { We also illustrate some modifications of the theory of gravity: Modified Newtonian Dynamics (MOND), MOdified Gravity (MOG), and $f(R)$ gravity.
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I. Martino, S. Chakrabarty, V. Cesare, et. al.
Fri, 31 Jul 20
-640/69
Comments: 70 pages; 27 Figures; Invited Review accepted for publication on Universe. Special Issue “Theories of Gravity: Alternatives to the Cosmological and Particle Standard Models”
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Characterizing Quasar CIV Emission-line Measurements from Time-resolved Spectroscopy [GA]
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http://arxiv.org/abs/2007.15120
We use multi-epoch quasar spectroscopy to determine how accurately single-epoch spectroscopy can locate quasars in emission-line parameter space in order to inform investigations where time-resolved spectroscopy is not available. We explore the improvements in emission-line characterization that result from using non-parametric information from many lines as opposed to a small number of parameters for a single line, utilizing reconstructions based on an independent component analysis applied to the data from the Sloan Digital Sky Survey Reverberation Mapping project. We find that most of the quasars are well described by just two components, while more components signal a quasar likely to yield a successful reverberation mapping analysis. In single-epoch spectroscopy the apparent variability of equivalent width is exaggerated because it is dependent on the continuum. Multi-epoch spectroscopy reveals that single-epoch results do not significantly change where quasars are located in CIV parameter space and do not have a significant impact on investigations of the global Baldwin Effect. Quasars with emission line properties indicative of higher $L/L_{Edd}$ are less variable, consistent with models with enhanced accretion disk density. Narrow absorption features at the systemic redshift may be indicative of orientation (including radio-quiet quasars) and may appear in as much as 20% of the quasar sample. Future work applying these techniques to lower luminosity quasars will be important for understanding the nature of accretion disk winds.
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A. Rivera, G. Richards, P. Hewett, et. al.
Fri, 31 Jul 20
-639/69
Comments: Submitted to ApJ June 19, 2024, Accepted July 13, 2024
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Confirmed width-Eiso and width-Liso relations in GRB: comparison with the Amati and Yonetoku relations [HEAP]
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http://arxiv.org/abs/2007.15443
In this paper, we select a sample including 141 BEST time-integrated F spectra and 145 BEST peak flux P spectra observed by the Konus-Wind with known redshift to recheck the connection between the spectral width and $E_{iso}$ as well as $L_{iso}$. We define six types of absolute spectral widths. It is found that all of the rest-frame absolute spectral widths are strongly positive correlated with $E_{iso}$ as well as $L_{iso}$ for the long burst for both the F and P spectra. All of the short bursts are the outliers for width-$E_{iso}$ relation and most of the short bursts are consistent with the long bursts for the width-$L_{iso}$ relation for both F and P spectra. Moreover, all of the location energy, $E_{2}$ and $E_{1}$, corresponding to various spectral widths are also positive correlated with $E_{iso}$ as well as $L_{iso}$. We compare all of the relations with the Amati and Yonetoku relations and find the width-$E_{iso}$ and width-$L_{iso}$ relations when the widths are at about 90\% maximum of the $EF_{E}$ spectra almost overlap with Amati relation and Yonetoku relation, respectively. The correlations of $E_{2}-E_{iso}$, $E_{1}-E_{iso}$ and $E_{2}-L_{iso}$, $E_{1}-L_{iso}$ when the location energies are at 99\% maximum of the $EF_{E}$ spectra are very close to the Amati and Yonetoku relations, respectively. Therefore, we confirm the existence of tight width-$E_{iso}$ and width-$L_{iso}$ relations for long bursts. We further show that the spectral shape is indeed related to $E_{iso}$ and $L_{iso}$. The Amati and Yonetoku relations are not necessarily the best relationships to relate the energy to the $E_{iso}$ and $L_{iso}$. They may be the special cases of the width-$E_{iso}$ and width-$L_{iso}$ relations or the energy-$E_{iso}$ and energy-$L_{iso}$ relations.
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Z. Peng, Y. Yin, T. Li, et. al.
Fri, 31 Jul 20
-638/69
Comments: 25 pages,25 figures,8 tables, accepted for publication in The Astrophysical Journal. arXiv admin note: text overlap with arXiv:1908.04663 by other authors
Coronal loops reveal crucial information about the nature of both coronal magnetic fields and coronal heating. The shape of the corresponding flux tube cross section and how it varies with position are especially important properties. They are a direct indication of the expansion of the field and of the cross-field spatial distribution of the heating. We have studied 20 loops using high spatial resolution observations from the first flight of the Hi-C rocket experiment, measuring the intensity and width as a function of position along the loop axis. We find that intensity and width tend to either be uncorrelated or to have a direct dependence, such that they increase or decrease together. This implies that the flux tube cross sections are approximately circular under the assumptions that the tubes have non-negligible twist and that the plasma emissivity is approximately uniform along the magnetic field. The shape need not be a perfect circle and the emissivity need not be uniform within the cross section, but sub-resolution patches of emission must be distributed quasi-uniformly within an envelope that has an aspect ratio of order unity. This raises questions about the suggestion that flux tubes expand with height, but primarily in the line-of-sight direction so that the corresponding (relatively noticeable) loops appear to have roughly uniform width, a long-standing puzzle. It also casts doubt on the idea that most loops correspond to simple warped sheets, although we leave open the possibility of more complex manifold structures.
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J. Klimchuk and C. DeForest
Fri, 31 Jul 20
-637/69
Comments: 27 pages, 9 figures, accepted by Astrophysical Journal
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The Galactic origin for the borders in the Earth history [EPA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15187
The external galactic key factor for developing of massive geochronological boundaries, as well as mass extinctions (ME) is proved based on chronological relationships of the impulses of globally short processes. External galactic key factor is also proved based on the coincidence of the scales of their developing processes, their regular periodicity in the formation of the boundaries of the Phanerozoic epochs and the presence of a unifying complex of cause-effect relationships for boundary processes. The hypotheses of the impact origin of ocean basins and plumes are substantiated, the assumptions about the unsteady nature of the Spiral Arms and the rotational acceleration of the Milky Ways core are confirmed.
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R. Nigmatzyanov
Fri, 31 Jul 20
-636/69
Comments: Published in the journal Otechestvennaya geologiya [National geology], 2015, 3. pp.70-83
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http://arxiv.org/abs/2007.15529
Understanding the atmospheres of exoplanets is a milestone to decipher their formation history and potential habitability. High-contrast imaging and spectroscopy of exoplanets is the major pathway towards the goal. Directly imaging of an exoplanet requires high spatial resolution. Interferometry has proven to be an effective way of improving spatial resolution. However, means of combining interferometry, high-contrast imaging, and high-resolution spectroscopy have been rarely explored. To fill in the gap, we present the dual-aperture fiber nuller (FN) for current-generation 8-10 meter telescopes, which provides the necessary spatial and spectral resolution to (1) conduct follow-up spectroscopy of known exoplanets; and (2) detect planets in debris-disk systems. The concept of feeding a FN to a high-resolution spectrograph can also be used for future space and ground-based missions. We present a case study of using the dual-aperture FN to search for biosignatures in rocky planets around M stars for a future space interferometry mission. Moreover, we discuss how a FN can be equipped on future extremely large telescopes by using the Giant Magellan Telescope (GMT) as an example.
We present a joint cosmological analysis of weak gravitational lensing observations from the Kilo-Degree Survey (KiDS-1000), with redshift-space galaxy clustering observations from the Baryon Oscillation Spectroscopic Survey (BOSS), and galaxy-galaxy lensing observations from the overlap between KiDS-1000, BOSS and the spectroscopic 2-degree Field Lensing Survey (2dFLenS). This combination of large-scale structure probes breaks the degeneracies between cosmological parameters for individual observables, resulting in a constraint on the structure growth parameter $S_8=\sigma_8 \sqrt{\Omega_{\rm m}/0.3} = 0.766^{+0.020}{-0.014}$, that has the same overall precision as that reported by the full-sky cosmic microwave background observations from Planck. The recovered $S_8$ amplitude is low, however, by $8.3 \pm 2.6$ % relative to Planck. This result builds from a series of KiDS-1000 analyses where we validate our methodology with variable depth mock galaxy surveys, our lensing calibration with image simulations and null-tests, and our optical-to-near-infrared redshift calibration with multi-band mock catalogues and a spectroscopic-photometric clustering analysis. The systematic uncertainties identified by these analyses are folded through as nuisance parameters in our cosmological analysis. Inspecting the offset between the marginalised posterior distributions, we find that the $S_8$-difference with Planck is driven by a tension in the matter fluctuation amplitude parameter, $\sigma_8$. We quantify the level of agreement between the CMB and our large-scale structure constraints using a series of different metrics, finding differences with a significance ranging between $\sim! 3\,\sigma$, when considering the offset in $S{8}$, and $\sim! 2\,\sigma$, when considering the full multi-dimensional parameter space.
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C. Heymans, T. Tröster, M. Asgari, et. al.
Fri, 31 Jul 20
-634/69
Comments: 24 pages, 11 figures, 5 tables, submitted to A&A. This paper is part of the KiDS-1000 series of papers, accompanying Asgari et al. and Hildebrandt et al. appearing on the arXiv today, joining Joachimi et al. (伕理http) and Giblin et al. (arXiv:2007.01845). Online KiDS-1000 talks and seminars can be viewed at this http URL
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Oceanic and atmospheric methane cycling in the cGENIE Earth system model [CL]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15053
The methane cycle is a key component of the Earth system that links planetary climate, biological metabolism, and the global biogeochemical cycles of carbon, oxygen, sulfur, and hydrogen. However, currently lacking is a numerical model capable of simulating a diversity of environments in the ocean where methane can be produced and destroyed, and with the flexibility to be able to explore not only relatively recent perturbations to Earth’s methane cycle but also to probe methane cycling and associated climate impacts under the reducing conditions characteristic of most of Earth history and likely widespread on other Earth-like planets. Here, we present an expansion of the ocean-atmosphere methane cycle in the intermediate-complexity Earth system model cGENIE, including parameterized atmospheric photochemistry and schemes for microbial methanogenesis, aerobic methanotrophy, and anaerobic oxidation of methane. We describe the model framework, compare model parameterizations against modern observations, and illustrate the flexibility of the model through a series of example simulations. Though we make no attempt to rigorously tune default model parameters, we find that simulated atmospheric methane levels and marine dissolved methane distributions are generally in good agreement with empirical constraints for the modern and recent Earth. Finally, we illustrate the model’s utility in understanding the time-dependent behavior of the methane cycle resulting from transient carbon injection into the atmosphere, and present model ensembles that examine the effects of oceanic chemistry and the thermodynamics of microbial metabolism on steady-state atmospheric methane abundance.
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C. Reinhard, S. Olson, S. Turner, et. al.
Fri, 31 Jul 20
-633/69
Comments: Manuscript in review at Geoscientific Model Development
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Dark Energy Survey Year 1 Results: Constraining Baryonic Physics in the Universe [CEA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15026
Measurements of large-scale structure are interpreted using theoretical predictions for the matter distribution, including potential impacts of baryonic physics. We constrain the feedback strength of baryons jointly with cosmology using weak lensing and galaxy clustering observables (3$\times$2pt) of Dark Energy Survey (DES) Year 1 data in combination with external information from baryon acoustic oscillations (BAO) and Planck cosmic microwave background polarization. Our baryon modeling is informed by a set of hydrodynamical simulations that span a variety of baryon scenarios; we span this space via a Principal Component (PC) analysis of the summary statistics extracted from these simulations. We show that at the level of DES Y1 constraining power, one PC is sufficient to describe the variation of baryonic effects in the observables, and the first PC amplitude ($Q_1$) generally reflects the strength of baryon feedback. With the upper limit of $Q_1$ prior being bound by the Illustris feedback scenarios, we reach $\sim 20\%$ improvement in the constraint of $S_8=\sigma_8(\Omega_{\rm m}/0.3)^{0.5}=0.788^{+0.018}太阳HTTP伕理-企业级优质HTTP爬虫伕理ip池定制服务平台:2021-4-7 · 太阳HTTP伕理是企业级高质量HTTP伕理IP供应平台，海量优质 HTTP、HTTPS、Socks伕理IP资源，先后为百家企业提供大数据采集伕理IP解 决方案{-0.015}$ for the combined DES Y1+Planck EE+BAO analysis with a non-informative $Q_1$ prior. In terms of the baryon constraints, we measure $Q_1=1.14^{+2.20}太阳HTTP伕理-企业级优质HTTP爬虫伕理ip池定制服务平台:2021-4-7 · 太阳HTTP伕理是企业级高质量HTTP伕理IP供应平台，海量优质 HTTP、HTTPS、Socks伕理IP资源，先后为百家企业提供大数据采集伕理IP解 决方案{-1.48}$ for DESY1+Planck EE+BAO, allowing us to exclude one of the most extreme AGN feedback hydrodynamical scenario at more than $2 \sigma$.
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H. Huang, T. Eifler, R. Mandelbaum, et. al.
Fri, 31 Jul 20
-632/69
Comments: 24 pages, 18 figures, 2 tables. submitted to MNRAS. A brief video summary of this paper is available at 伕理http
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The hierarchical fragmentation of filaments and the role of sub-filaments [GA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.15358
Recent observations have revealed the presence of small fibres or sub-filaments within larger filaments. We present a numerical fragmentation study of fibrous filaments investigating the link between cores and sub-filaments using hydrodynamical simulations performed with the moving-mesh code Arepo. Our study suggests that cores form in two environments: (i) as isolated cores, or small chains of cores, on a single sub-filament, or (ii) as an ensemble of cores located at the junction of sub-filaments. We term these isolated and hub cores respectively. We show that these core populations are statistically different from each other. Hub cores have a greater mean mass than isolated cores, and the mass distribution of hub cores is significantly wider than isolated cores. This fragmentation is reminiscent of parsec-scale hub-filament systems, showing that the combination of turbulence and gravity leads to similar fragmentation signatures on multiple scales, even within filaments. Moreover, the fact that fragmentation proceeds through sub-filaments suggests that there exists no characteristic fragmentation length-scale between cores. This is in opposition to earlier theoretical works studying fibre-less filaments which suggest a strong tendency towards the formation of quasi-periodically spaced cores, but in better agreement with observations. We also show tentative signs that global collapse of filaments preferentially form cores at both filament ends, which are more massive and dense than other cores.
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S. Clarke, G. Williams and S. Walch
Fri, 31 Jul 20
-631/69
Comments: Accepted in MNRAS. 13 pages and 13 figures, 8 page appendix and 7 figures
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http://arxiv.org/abs/2007.15278
The coded aperture imaging technique is a useful method of X-ray imaging in observational astrophysics. However, the presence of imaging noise or so-called artifacts in a decoded image is a drawback of this method. We propose a new coded aperture imaging method using multiple different random patterns for significantly reducing the image artifacts. This aperture mask contains multiple different patterns each of which generates a different artifact distribution in its decoded image. By summing all decoded images of the different patterns, the artifact distributions are cancelled out, and we obtain a remarkably accurate image. We demonstrate this concept with imaging experiments of a monochromatic 16 keV hard X-ray beam at the synchrotron photon facility SPring-8, using the combination of a CMOS image sensor and an aperture mask that has four different random patterns composed of holes with a diameter of 27 um and a separation of 39 um. The entire imaging system is installed in a 25 cm-long compact size, and achieves an angular resolution of < 30” (full width at half maximum). In addition, we show by Monte Carlo simulation that the artifacts can be reduced more effectively if the number of different patterns increases to 8 or 16.
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T. Kasuga, H. Odaka, K. Hatauchi, et. al.
Fri, 31 Jul 20
-630/69
Comments: 20 pages, 8 figures, accepted for publication in JATIS
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http://arxiv.org/abs/2007.15365
Seeing, the angular size of stellar images blurred by atmospheric turbulence, is a critical parameter used to assess the quality of astronomical sites. Median values at the best mid-latitude sites are generally in the range of 0.6–0.8\,arcsec. Sites on the Antarctic plateau are characterized by comparatively-weak turbulence in the free-atmosphere above a strong but thin boundary layer. The median seeing at Dome C is estimated to be 0.23–0.36 arcsec above a boundary layer that has a typical height of 30\,m. At Dome A and F, the only previous seeing measurements were made during daytime. Here we report the first direct measurements of night-time seeing at Dome A, using a Differential Image Motion Monitor. Located at a height of just 8\,m, it recorded seeing as low as 0.13\,arcsec, and provided seeing statistics that are comparable to those for a 20\,m height at Dome C. It indicates that the boundary layer was below 8\,m 31\% of the time. At such times the median seeing was 0.31\,arcsec, consistent with free-atmosphere seeing. The seeing and boundary layer thickness are found to be strongly correlated with the near-surface temperature gradient. The correlation confirms a median thickness of approximately 14\,m for the boundary layer at Dome A, as found from a sonic radar. The thinner boundary layer makes it less challenging to locate a telescope above it, thereby giving greater access to the free-atmosphere.
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B. Ma, Z. Shang, Y. Hu, et. al.
Fri, 31 Jul 20
-629/69
Ultraviolet-Based Science in the Solar System: Advances and Next Steps [IMA]
Posted on by arxiverbot
http://arxiv.org/abs/2007.14993
We review the importance of recent UV observations of solar system targets and discuss the need for further measurements, instrumentation and laboratory work in the coming decade. In the past decade, numerous important advances have been made in solar system science using ultraviolet (UV) spectroscopic techniques. Formerly used nearly exclusively for studies of giant planet atmospheres, planetary exospheres and cometary emissions, UV imaging spectroscopy has recently been more widely applied. The geyser-like plume at Saturn’s moon Enceladus was discovered in part as a result of UV stellar occultation observations, and this technique was used to characterize the plume and jets during the entire Cassini mission. Evidence for a similar style of activity has been found at Jupiter’s moon Europa using Hubble Space Telescope (HST) UV emission and absorption imaging. At other moons and small bodies throughout the solar system, UV spectroscopy has been utilized to search for activity, probe surface composition, and delineate space weathering effects; UV photometric studies have been used to uncover regolith structure. Insights from UV imaging spectroscopy of solar system surfaces have been gained largely in the last 1-2 decades, including studies of surface composition, space weathering effects (e.g. radiolytic products) and volatiles on asteroids (e.g. [2][39][48][76][84]), the Moon (e.g. [30][46][49]), comet nuclei (e.g. [85]) and icy satellites (e.g. [38][41-44][45][47][65]). The UV is sensitive to some species, minor contaminants and grain sizes often not detected in other spectral regimes. In the coming decade, HST observations will likely come to an end. New infrastructure to bolster future UV studies is critically needed. These needs include both developmental work to help improve future UV observations and laboratory work to help interpret spacecraft data. UV instrumentation will be a critical tool on missions to a variety of targets in the coming decade, especially for the rapidly expanding application of UV reflectance investigations of atmosphereless bodies.
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A. Hendrix, T. Becker, D. Bodewits, et. al.
Fri, 31 Jul 20
-628/69
Comments: N/A
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http://arxiv.org/abs/2007.15635
We present redshift distribution estimates of galaxies selected from the fourth data release of the Kilo-Degree Survey over an area of $\sim1000$ deg$^2$ (KiDS-1000). These redshift distributions represent one of the crucial ingredients for weak gravitational lensing measurements with the KiDS-1000 data. The primary estimate is based on deep spectroscopic reference catalogues that are re-weighted with the help of a self-organising-map (SOM) to closely resemble the KiDS-1000 sources, split into five tomographic redshift bins in the photometric redshift range $0.1<z_\mathrm{B}\le1.2$. Sources are selected such that they only occupy that volume of 9-dimensional magnitude-/colour-space that is also covered by the reference samples (`gold’ selection). Residual biases in the mean redshifts determined from this calibration are estimated from mock catalogues to be $\lesssim0.01$ for all five bins with uncertainties of $\sim 0.01$. This primary SOM estimate of the KiDS-1000 redshift distributions is complemented with an independent clustering redshift approach. After validation of the clustering-$z$ on the same mock catalogues and a careful assessment of systematic errors, we find no significant bias of the SOM redshift distributions with respect to the clustering-$z$ measurements. The SOM redshift distributions re-calibrated by the clustering-$z$ represent an alternative calibration of the redshift distributions with only slightly larger uncertainties in the mean redshifts of $\sim 0.01-0.02$ to be used in KiDS-1000 cosmological weak lensing analyses. As this includes the SOM uncertainty, clustering-$z$ are shown to be fully competitive on KiDS-1000 data.
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H. Hildebrandt, J. Busch, A. Wright, et. al.
Fri, 31 Jul 20
-627/69
Comments: 14 pages, 7 figures, 3 tables, submitted to A&A. This paper is part of the KiDS-1000 series of papers, accompanying Heymans, Tr\”oster et al. and Asgari et al. appearing on the arXiv today, joining Joachimi et al. (arXiv:2007.01844) and Giblin et al. (arXiv:2007.01845). Online KiDS-1000 talks and seminars can be viewed at this http URL
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http://arxiv.org/abs/2007.14996
Neural network (NN) based methods are applied to the detection of radio frequency interference (RFI) in post-correlation,post-calibration time/frequency data. While calibration doesaffect RFI for the sake of this work a reduced dataset inpost-calibration is used. Two machine learning approachesfor flagging real measurement data are demonstrated usingthe existing RFI flagging technique AOFlagger as a groundtruth. It is shown that a single layer fully connects networkcan be trained using each time/frequency sample individuallywith the magnitude and phase of each polarization and Stokesvisibilities as features. This method was able to predict aBoolean flag map for each baseline to a high degree of accuracy achieving a Recall of 0.69 and Precision of 0.83 and anF1-Score of 0.75.
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K. Harrison and A. Mishra
Fri, 31 Jul 20
-626/69
Comments: This paper has been published in the Proceedings of RFI 2024 Workshop by IEEE Xplorer at: 伕理http
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Considerations for Atmospheric Retrieval of High-Precision Brown Dwarf Spectra [EPA]
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http://arxiv.org/abs/2007.15004
Isolated brown dwarfs provide remarkable laboratories for understanding atmospheric physics in the low-irradiation regime, and can be observed more precisely than exoplanets. As such, they provide a glimpse into the future of high-SNR observations of exoplanets. In this work, we investigate several new considerations that are important for atmospheric retrievals of high-quality thermal emission spectra of sub-stellar objects. We pursue this using an adaptation of the HyDRA atmospheric retrieval code. We propose a parametric pressure-temperature (P-T) profile for brown dwarfs consisting of multiple atmospheric layers, parameterised by the temperature change across each layer. This model allows the steep temperature gradient of brown dwarf atmospheres to be accurately retrieved while avoiding commonly-encountered numerical artefacts. The P-T model is especially flexible in the photosphere, which can reach a few tens of bar for T-dwarfs. We demonstrate an approach to include model uncertainties in the retrieval, focusing on uncertainties introduced by finite spectral and vertical resolution in the atmospheric model used for retrieval (~8\% in the present case). We validate our retrieval framework by applying it to a simulated data set and then apply it to the HST/WFC3 spectrum of the T-dwarf 2MASS J2339+1352. We retrieve sub-solar abundances of H2O and CH4 in the object at ~0.1 dex precision. Additionally, we constrain the temperature structure to within ~100 K in the photosphere. Our results demonstrate the promise of high-SNR spectra to provide high-precision abundance estimates of sub-stellar objects.
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A. Piette and N. Madhusudhan
Fri, 31 Jul 20
-625/69
Comments: Accepted for publication in MNRAS, 21 pages, 15 figures
The break-by-one gamma distribution has a probability density function resembling the Schechter function, but with the small-argument behavior modified so it is normalizable in commonly arising cases where the Schechter function is not. Its connection to the gamma distribution makes it straightforward to sample from. These properties make it useful for cosmic demographics.
We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB1 East molecular cloud. We combine observations of dust polarised emission from the Planck telescope and CO molecular line emission observations from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculate the strength of the plane-of-the-sky magnetic field using a modified Chandrasekhar-Fermi method and estimate mass over flux ratios in different regions of the cloud. We use the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. The molecular complex shows an ordered large-scale plane-of-the-sky magnetic field structure. In the Northern part, it is mostly orientated along the filamentary structures while the Southern part shows at least two regions with distinct magnetic field orientations. We find that in the Northern filaments the magnetic field is unlikely to provide support against fragmentation at large scales. Our analysis reveals a shock region in the Northern part of the complex right in-between two filamentary clouds which were previously suggested to be in collision. Moreover, the shock seems to extend farther towards the Western part of the complex. In the Southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it was dragged by the matter towards the densest regions. The large-scale magnetic field in Monoceros OB-1 East molecular clouds is tightly connected to the global structure of the complex and, in the Northern part, it seems to be dominated by gravity and turbulence, while in the Southern part it influences the structuring of matter.
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D. Alina, J. Montillaud, Y. Hu, et. al.
Fri, 31 Jul 20
-623/69
Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of $-1.83\pm0.29$ broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope (GMRT) at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.
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S. Duchesne, M. Johnston-Hollitt, Z. Zhu, et. al.
Fri, 31 Jul 20
-622/69
Comments: 17 pages, 16 figures, accepted for publication in Publications of the Astronomical Society of Australia (PASA)
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Dark D-Brane Cosmology: from background evolution to cosmological perturbations [CL]
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We study the cosmological predictions of the dark D-brane model, in which dark matter resides on a D-brane moving in a higher-dimensional space. By construction, dark matter interacts only gravitationally with the standard model sector in this framework. The dark energy scalar field is associated with the position of the D-brane, and its dynamics is encoded in a Dirac-Born-Infeld action. On the other hand, dark matter is identified with matter on the D-brane, that naturally couples to dark energy \textit{via} a disformal coupling. We analyse the numerical evolution of the cosmological background, highlighting the fact that there are two regimes of interest: one, in which the coupling is positive throughout; and another, in which the coupling is negative at the present. In the latter, there is the enticing possibility of having scenarios in which the coupling is positive for a significant part of the evolution, before decreasing towards negative values. In both cases, the coupling is very small at early times, and only starts to grow during the late matter dominated era. We also derive the equations for the linear cosmological perturbations, an expression for the effective time-dependent gravitational coupling between dark matter particles and present the numerical results for the CMB anisotropy and matter power spectra. This allows for a direct comparison of the predictions for the growth of large scale structure with other disformal quintessence models.
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C. Bruck and E. Teixeira
Fri, 31 Jul 20
-621/69
Comments: 24 pages, 6 figures
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LBT transmission spectroscopy of HAT-P-12b: confirmation of a cloudy atmosphere with no significant alkali features [EPA]
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http://arxiv.org/abs/2007.15485
The hot sub-Saturn-mass exoplanet HAT-P-12b is an ideal target for transmission spectroscopy because of its inflated radius. We observed one transit of the planet with the multi-object double spectrograph (MODS) on the Large Binocular Telescope (LBT) with the binocular mode and obtained the atmosphere transmission spectrum with a wavelength coverage of $\sim$ 0.4 — 0.9 $\mathrm{\mu}$m. The spectrum is relatively flat and does not show any significant sodium or potassium absorption features. Our result is consistent with the revised Hubble Space Telescope (HST) transmission spectrum of a previous work, except that the HST result indicates a tentative detection of potassium. The potassium discrepancy could be the result of statistical fluctuation of the HST dataset. We fitted the planetary transmission spectrum with an extensive grid of cloudy models and confirm the presence of high-altitude clouds in the planetary atmosphere. The fit was performed on the combined LBT and HST spectrum, which has an overall wavelength range of 0.4 — 1.6 $\mathrm{\mu}$m. The LBT/MODS spectrograph has unique advantages in transmission spectroscopy observations because of its capabilities of covering a large wavelength range with a single exposure and acquiring two sets of independent spectra simultaneously.
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F. Yan, N. Espinoza, K. Molaverdikhani, et. al.
Fri, 31 Jul 20
-620/69
Results on low-mass weakly interacting massive particles from a 11 kg-day target exposure of DAMIC at SNOLAB [CEA]
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http://arxiv.org/abs/2007.15622
We present constraints on the existence of weakly interacting massive particles (WIMPs) from a 11 kg-day target exposure of the DAMIC experiment at the SNOLAB underground laboratory. The observed energy spectrum and spatial distribution of ionization events with electron-equivalent energies $>$200 eV${\rm ee}$ in the DAMIC CCDs are consistent with backgrounds from natural radioactivity. An excess of ionization events is observed above the analysis threshold of 50 eV${\rm ee}$. While the origin of this low-energy excess requires further investigation, our data exclude spin-independent WIMP-nucleon scattering cross sections $\sigma_{\chi-n}$ as low as $3\times 10^{-41}$ cm$^2$ for WIMPs with masses $m_{\chi}$ from 7 to 10 GeV$c^{-2}$ . These results are the strongest constraints from a silicon target on the existence of WIMPs with $m_{\chi}$$<$9 GeV$c^{-2}$ and are directly relevant to any dark matter interpretation of the excess of nuclear-recoil events observed by the CDMS silicon experiment in 2013.
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A. Aguilar-Arevalo, D. Amidei, D. Baxter, et. al.
Fri, 31 Jul 20
-619/69
We compute the decay spectrum for dark matter (DM) with masses above the scale of electroweak symmetry breaking, all the way to the Planck scale. For an arbitrary hard process involving a decay to the unbroken standard model, we determine the prompt distribution of stable states including photons, neutrinos, positrons, and antiprotons. These spectra are a crucial ingredient in the search for DM via indirect detection at the highest energies as being probed in current and upcoming experiments including IceCube, HAWC, CTA, and LHAASO. Our approach improves considerably on existing methods. For example, we include all relevant electroweak interactions. The importance of these effects grow with DM mass, and by an EeV our spectra can differ by orders of magnitude from existing results.
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C. Bauer, N. Rodd and B. Webber
Fri, 31 Jul 20
-618/69
Comments: 8+24 pages, 3+12 figures, comments welcome. Spectra available at this https URL
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http://arxiv.org/abs/2007.15329
We report results from the analysis of XMM-Newton and INTEGRAL data of IGR J16479-4514. The unpublished XMM-Newton observation, performed in 2012, occurred during the source eclipse. No point-like X-ray emission was detected from the source, conversely extended X-ray emission was clearly detected up to a size distance compatible with a dust scattering halo produced by the source X-ray emission before being eclipsed by its companion donor star. The diffuse emission of the dust-scattering halo could be observed without any contamination from the central point X-ray source, compared to a previous XMM-Newton observation published in 2008. Our comprehensive analysis of the 2012 unpublished spectrum of the diffuse emission as well as of the 2008 re-analysed spectra extracted from three adjacent time intervals and different extraction regions (optimized for point-like and extended emission) allowed us to clearly disentangle the scattering halo spectrum from the residual point-like emission during the 2008 eclipse. Moreover, the point-like emission detected in 2008 could be separated into two components attributed to the direct emission from the source and to scattering in the stellar wind, respectively. From archival unpublished INTEGRAL data, we identified a very strong (3$\times$10$^{-8}$ erg cm$^{-2}$ s$^{-1}$) and fast (25 minutes duration) flare which was classified as giant hard X-ray flare since the measured peak-luminosity is 7$\times$10$^{37}$ erg s$^{-1}$. Giant X-ray flares from SFXTs are very rare, to date only one has been reported from a different source. We propose a physical scenario to explain the origin in the case of IGR J16479-4514.
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V. Sguera, A. Tiengo, L. Sidoli, et. al.
Fri, 31 Jul 20
-617/69
Comments: Accepted for publication on The Astrophysical Journal (received 20-Apr-2024, accepted 27-Jul-2024)
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http://arxiv.org/abs/2007.15593
The Rezzolla-Zhidenko (RZ) framework provides an efficient approach to characterize spherically symmetric black-hole spacetimes in arbitrary metric theories of gravity using a small number of variables [L. Rezzolla and A. Zhidenko, Phys. Rev. D. 90, 084009 (2014)]. These variables can be obtained in principle from near-horizon measurements of various astrophysical processes, thus potentially enabling efficient tests of both black-hole properties and the theory of general relativity in the strong-field regime. Here, we extend this framework to allow for the parametrization of arbitrary asymptotically-flat, spherically symmetric metrics and introduce the notion of a 11-dimensional (11D) parametrization space $\Pi$, on which each solution can be visualised as a curve or surface. An $\mathscr{L}^2$ norm on this space is used to measure the deviation of a particular compact object solution from the Schwarzschild black-hole solution. We calculate various observables, related to particle and photon orbits, within this framework and demonstrate that the relative errors we obtain are low (about $10^{-6}$). In particular, we obtain the innermost stable circular orbit (ISCO) frequency, the unstable photon-orbit impact parameter (shadow radius), the entire orbital angular speed profile for circular Kepler observers and the entire lensing deflection angle curve for various types of compact objects, including non-singular and singular black holes, boson stars and naked singularities, from various theories of gravity. Finally, we provide in a tabular form the first 11 coefficients of the fourth-order RZ parameterization needed to describe a variety of commonly used black-hole spacetimes. When comparing with the first-order RZ parameterization of astrophysical observables such as the ISCO frequency, the coefficients provided here increase the accuracy of two orders of magnitude or more.
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P. Kocherlakota and L. Rezzolla
Fri, 31 Jul 20
-616/69
We investigate binary lenses with $1/r^n$ potentials in the asymmetric case with two lenses with different indexes $n$ and $m$. These kinds of potentials have been widely used in several contexts, ranging from galaxies with halos described by different power laws to lensing by wormholes or exotic matter. In this paper, we present a complete atlas of critical curves and caustics for mixed binaries, starting from the equal-strength case, and then exploring unequal-strength systems. We also calculate the transitions between all different topology regimes. Finally we find some useful analytic approximations for the wide binary case and for the extreme unequal-strength case.
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V. Bozza, S. Pietroni and C. Melchiorre
Fri, 31 Jul 20
-615/69
Comments: 25 pages, 18 figures, in press on Universe, special issue Gravitational Lensing and Optical Geometry: A Centennial Perspective
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An X-ray Luminosity-dependent "Changing-look" Phenomenon in UGC\,3223 [GA]
The nature of the rare “Changing-look” (CL) phenomenon in active galactic nuclei (AGNs) is still under debate at current stage. We here present \it Swift/\rm XRT and UVOT follow-up observations of UGC\,3223, a newly discovered repeat CL-AGN with type transitions of $\mathrm{S1.5\rightarrow S2 \rightarrow S1.8}$ occurring in a period of about 30 years. By comparing the values previously reported in the \it ROSAT \rm All-sky Survey and in the second Swift-XRT Point Source catalog, we clearly find that the X-ray flux tightly follows the optical spectral transition, in which a spectral type closer to a Seyfert 1 type is associated with a higher X-ray flux. An invariable X-ray spectral shape is, however, found in the CL phenomenon of the object. An extremely low Eddington ratio of $\sim2\times10^{-4}$ can be obtained from the X-ray luminosity for its Seyfert 2 state, which suggests a favor of the disk-wind broad-line region model in explaining the CL phenomenon. A variation of the total UV emission is not revealed when compared to the previous \it GALEX \rm NUV observation, since the UVOT images indicate that $\sim90$\% UV emission comes from the intensive star formation in the host galaxy.
We present a novel numerical scheme for simulating the motion of relativistic charged particles in magnetospheres of compact objects, typically filled with highly magnetized collisionless plasmas. The new algorithm is based on a dynamic switch between the full system of equations of motion and a guiding center approximation. The switch between the two formulations is based on the magnetization of the plasma particles, such that the dynamics are accurately captured by the guiding center motion even when the gyro-frequency is under-resolved by the time step. For particles with a large gyro-radius, due to acceleration in, e.g., reconnecting current sheets, the algorithm adaptively switches to solve the full equations of motion instead. The new scheme is directly compatible with standard Particle-in-Cell codes, and is readily applicable in curved spacetimes via a dedicated covariant formulation. We test the performance of the coupled algorithm by evolving charged particles in electromagnetic configurations of reconnecting current sheets in magnetized plasma, obtained from special- and general-relativistic Particle-in-Cell simulations. The new coupled pusher is capable of producing highly accurate particle trajectories even when the time step is many orders of magnitude larger than the gyro-period, substantially reducing the restrictions of the temporal resolution.
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F. Bacchini, B. Ripperda, A. Philippov, et. al.
Thu, 30 Jul 20
-611/71
Comments: Submitted to ApJS
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The Uchuu Simulations: Data Release 1 and Dark Matter Halo Concentrations [CEA]
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http://arxiv.org/abs/2007.14720
We introduce the Uchuu suite of large high-resolution cosmological $N$-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion ($12800^3$) dark matter particles in a box of 2.0 Gpc/h, and the mass of each particle is $3.27 \times 10^{8}$ Msun/h. The highest resolution simulation, called Shin-Uchuu, consists of 262 billion ($6400^3$) particles in a box of 140 Mpc/h, with a particle mass of $8.97 \times 10^{5}$ Msun/h. Combining these simulations we can follow the evolution of dark matter haloes (and subhaloes) spanning from dwarf galaxies to massive galaxy cluster hosts. We present basic statistics, dark matter power spectra and halo (subhalo) mass function, to demonstrate the huge dynamic range and superb statistics of the Uchuu simulations. From the analysis of the evolution of the power spectra we conclude that our simulations are accurate enough from the Baryon Acoustic Oscillations up to very small scales. We also provide parameters of a mass-concentration model, which describes the evolution of halo concentrations, that reproduces our simulation data within 5% error. We make publicly available various $N$-body products, as part of Uchuu Data Release 1, on the Skies & Universes site. We also plan to release gravitational lensing maps, mock galaxy, X-ray cluster and active galactic nuclei catalogues in the near future.
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T. Ishiyama, F. Prada, A. Klypin, et. al.
Thu, 30 Jul 20
-610/71
Comments: 18 pages, 12 figures, We release various $N$-body products as data release 1 on this http URL such as subsets of simulation particles, matter power spectra, halo/subhalo catalogues, and their merger trees
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http://arxiv.org/abs/2007.14414
We study the hypothesis of high metallicity clumps being responsible for the abundance discrepancy found in planetary nebulae between the values obtained from recombination and collisionaly excited lines. We generate grids of photoionization models combining cold metal-rich clumps emitting the heavy element recombination lines, embedded in a normal metallicity region responsible for the forbidden lines. The two running parameters of the grid are the metallicity of the clumps and its volume fraction relative to the whole nebula. We determine the density and temperatures (from the Balmer jump and the [OIII] 5007/4363 A line ratio), and the ionic abundances from the collisional and recombination lines, as an observer would do. The metallicity of the near-to-solar region is recovered, while the metallicity of the clumps is systematically underestimated, by up to 2 orders of magnitude. This is mainly because most of the H$\beta$ emission is coming from the “normal” region, and only the small contribution emitted by the metal-rich clumps should be used. We find that a given ADF(O$^{++}$) can be reproduced by a small amount of rich clumps, or a bigger amount of less rich clumps. Finally, comparing with the observations of NGC 6153 we find 2 models that reproduce its ADF(O$^{++}$) and the observed electron temperatures. We determine the fraction of oxygen embedded in the metal-rich region (with a fraction of volume less than 1%) to be roughly between 25% and 60% of the total amount of oxygen in the nebula (a few 10$^{-3} M_\odot$).
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V. Gómez-Llanos and C. Morisset
Thu, 30 Jul 20
-609/71
Comments: Accepted for publication in MNRAS
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NuSTAR View of TeV Blazar Mrk 501 [HEAP]
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http://arxiv.org/abs/2007.14600
We report the results of flux and spectral variability studies of all seven {\it Nuclear Spectroscopic Telescope Array (NuSTAR)} observations of TeV $\gamma-$ray emitting blazar Markarian (or Mrk) 501. We found strong evidence of intraday variability in 3-79 keV X-ray light curves (LCs) of Mrk 501 during four out of these seven observations. We examined spectral variability using a model-independent hardness-ratio analysis and found a general “harder-when-brighter” behaviour in two observations. We also investigated the nature of 3-79 keV X-ray spectra of TeV blazar Mrk 501 and found that five out of seven spectra are well described by the curved log-parabola models with photon indices (at 10 keV) $\alpha \sim$ 2.12-2.32 and a curvature $\beta \sim$ 0.15-0.28. The two other spectra are somewhat better represented by simple power-law models with photon indices 2.70 and 2.75. We briefly discuss available physical models to explain our results.
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A. Pandey
Thu, 30 Jul 20
-608/71
Comments: 13 pages, 3 figures, 3 tables, published in special issue “X-Ray Flux and Spectral Variability of Blazars” of Galaxies journal
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http://arxiv.org/abs/2007.14843
Pulsar candidate sifting is an essential process for discovering new pulsars. It aims to search for the most promising pulsar candidates from an all-sky survey, such as High Time Resolution Universe (HTRU), Green Bank Northern Celestial Cap (GBNCC), Five-hundred-meter Aperture Spherical radio Telescope (FAST), etc. Recently, machine learning (ML) is a hot topic in pulsar candidate sifting investigations. However, one typical challenge in ML for pulsar candidate sifting comes from the learning difficulty arising from the highly class-imbalance between the observation numbers of pulsars and non-pulsars. Therefore, this work proposes a novel framework for candidate sifting, named multi-input convolutional neural networks (MICNN). The MICNN is an architecture of deep learning with four diagnostic plots of a pulsar candidate as its inputs. To train our MICNN in a highly class-imbalanced dataset, a novel image augment technique, as well as a three-stage training strategy, is proposed. Experiments on observations from HTRU and GBNCC show the effectiveness and robustness of these proposed techniques. In the experiments on HTRU, our MICNN model achieves a recall of 0.962 and a precision rate of 0.967 even in a highly class-imbalanced test dataset.
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H. Lin, X. Li and Q. Zeng
Thu, 30 Jul 20
-607/71
Comments: 13 pages,7 figures, 4 tables
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The tidal remnant of an unusually metal-poor globular cluster [GA]
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http://arxiv.org/abs/2007.14577
Globular clusters are some of the oldest bound stellar structures observed in the Universe. They are ubiquitous in large galaxies and are believed to trace intense star formation events and the hierarchical build-up of structure. Observations of globular clusters in the Milky Way, and a wide variety of other galaxies, have found evidence for a metallicity floor', whereby no globular clusters are found with chemical (metal’) abundances below approximately 0.3 to 0.4 per cent of that of the Sun. The existence of this metallicity floor may reflect a minimum mass and a maximum redshift for surviving globular clusters to form, both critical components for understanding the build-up of mass in the universe. Here we report measurements from the Southern Stellar Streams Spectroscopic Survey of the spatially thin, dynamically cold Phoenix stellar stream in the halo of the Milky Way. The properties of the Phoenix stream are consistent with it being the tidally disrupted remains of a globular cluster. However, its metal abundance ([Fe/H] = -2.7) is substantially below that of the empirical metallicity floor. The Phoenix stream thus represents the debris of the most metal-poor globular cluster discovered so far, and its progenitor is distinct from the present-day globular cluster population in the local Universe. Its existence implies that globular clusters below the metallicity floor have probably existed, but were destroyed during Galactic evolution.
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Z. Wan, G. Lewis, T. Li, et. al.
Thu, 30 Jul 20
-606/71
Comments: Authors’ version of an Article published in Nature on July 29th, 2024
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Shape of solar cycles and mid-term solar activity oscillations [SSA]
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http://arxiv.org/abs/2007.14779
The evolution of the solar activity comprises, apart from the well-known 11-year cycle, various temporal scales ranging from months up to the secondary cycles known as mid-term oscillations. Its nature deserves a physical explanation. In this work, we consider the 5-to-6 year oscillations as derived both from sunspot and from solar magnetic dipole time series. Using the solar dynamo model, we deduced that these variations may be a manifestation of the dynamo nonlinearities and non-harmonic shape of the solar activity cycles. We conclude that the observed mid-term oscillations are related to the nonlinear saturation of the dynamo processes in the solar interior.
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D. Sokoloff, A. Shibalova, V. Obridko, et. al.
Thu, 30 Jul 20
-605/71
The observation of quasars at very high redshift such as Poniuaena is a challenge for models of super-massive black hole (SMBH) formation. This work presents a study of SMBH formation via known physical processes in star-burst clusters formed at the onset of the formation of their hosting galaxy. While at the early stages hyper-massive star-burst clusters reach the luminosities of quasars, once their massive stars die, the ensuing gas accretion from the still forming host galaxy compresses its stellar black hole (BH) component to a compact state overcoming heating from the BH–BH binaries such that the cluster collapses, forming a massive SMBH-seed within about a hundred Myr. Within this scenario the SMBH–spheroid correlation emerges near-to-exactly. The highest-redshift quasars may thus be hyper-massive star-burst clusters or young ultra-compact dwarf galaxies (UCDs), being the precursors of the SMBHs that form therein within about 200 Myr of the first stars. For spheroid masses <10^9.6 Msun a SMBH cannot form and instead only the accumulated nuclear cluster remains. The number evolution of the quasar phases with redshift is calculated and the possible problem of missing quasars at very high redshift is raised. SMBH-bearing UCDs and the formation of spheroids are discussed critically in view of the high redshift observations. A possible tension is found between the high star-formation rates (SFRs) implied by downsizing and the observed SFRs, which may be alleviated within the IGIMF theory and if the downsizing times are somewhat longer.
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P. Kroupa, L. Subr, T. Jerabkova, et. al.
Thu, 30 Jul 20
-604/71
Comments: 34 pages, 18 figures, MNRAS, in press
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http://arxiv.org/abs/2007.14624
Resolving faint galaxies in large volumes is critical for accurate cosmic reionisation simulations. While less demanding than hydrodynamical simulations, semi-analytic reionisation models still require very large N-body simulations in order to resolve the atomic cooling limit across the whole reionisation history within box sizes $\gtrsim 100 h^{-1}\text{Mpc}$. To facilitate this, we extend the mass resolution of N-body simulations using a Monte Carlo algorithm. Our extended halo catalogues are designed for semi-analytic galaxy formation models that utilise halo positions for reionisation calculations. To illustrate, we present an extended halo catalogue that reaches a mass resolution of $M_\text{halo} = 3.2 \times 10^7 h^{-1}\text{M}_\odot$ in a $105 h^{-1}\text{Mpc}$ box, equivalent to an N-body simulation with $\sim 6800^3$ particles. The results are verified using smaller volume N-body simulations with higher resolution. The extended halo catalogues are applied to the Meraxes semi-analytic reionisation model, producing stellar mass functions, star formation rate densities and volume-weighted neutral fractions that are consistent with those based on direct N-body halo merger trees up to $z \sim 10$. Comparison of high resolution large volume simulations with both small volume or low resolution simulations indicates that both low resolution and small volume simulations lead to reionisation ending too rapidly. Thus, both sufficient resolution and volume are required to correctly model the late stage of cosmic reionisation.
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Y. Qiu, S. Mutch, P. Elahi, et. al.
Thu, 30 Jul 20
-603/71
Comments: 14 pages, 13 figures. Submitted to MNRAS
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http://arxiv.org/abs/2007.14416
Time-delay cosmography in strongly lensed quasars offer an independent way of measuring the Hubble constant, $H_0$. However, it has been proposed that the combination of microlensing and source-size effects, also known as microlensing time delay can potentially increase the uncertainty in time-delay measurements as well as lead to a biased time delay. In this work, we first investigate how microlensing time delay changes with assumptions on the initial mass function (IMF) and find that the more massive microlenses produce the sharper distributions of microlensing time delays. However, we also find that the magnification probability distributions for different IMFs are indistinguishable from each other. Second, we present a new method to measure the color-dependent source size in lensed quasars using the microlensing time delays inferred from multi-band light curves. In practice the relevant observable is the differential microlensing time delays between different bands. We show from simulation using the LSST-like facility that if this differential time delay between bands can be measured with a precision of $0.1$ days in any given lensed image, the disk size can be recovered to within a factor of $2$. If four lensed images are used, our method is able to achieve an unbiased source measurement within error of the order of $20\%$, which is comparable with other techniques.
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J. Chan, K. Rojas, M. Millon, et. al.
Thu, 30 Jul 20
-602/71
Comments: 10 pages, 9 figures
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Gravitational wave background from extreme mass ratio inspirals [GA]
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http://arxiv.org/abs/2007.14403
Extreme mass ratio inspirals (EMRIs), i.e. binary systems comprised by a compact stellar-mass object orbiting a massive black hole, are expected to be among the primary gravitational wave (GW) sources for the forthcoming LISA mission. The astrophysical processes leading to the formation of such systems still remain poorly understood, resulting into large uncertainties in the predicted cosmic rate of these sources, spanning at least three orders of magnitude. As LISA can individually resolve mostly EMRIs up to $z\gtrsim1$, the ensemble of signals below its detection threshold will add up incoherently forming an unresolved confusion noise, which can be formally described as a stochastic background. We perform an extensive study of this background by considering a collection of astrophysically motivated EMRI formation scenarios, spanning current uncertainties. We find that in fiducial EMRI models — predicting hundreds of EMRI detections during mission operations — a significant background comparable to the LISA noise emerges, affecting the performance of the instrument around 3 mHz. In extreme cases, this background can even “erase” the whole LISA sensitivity bucket in the 2-10 mHz frequency range. This points to the need of a better understanding of EMRIs’ astrophysics for a full assessment of the LISA mission potential.
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M. Bonetti and A. Sesana
Thu, 30 Jul 20
-601/71
Comments: 19 pages, 12 figures, to be submitted to PRD
We present solar full-disk observations, which were recorded at the Einstein Tower during the years 1943 – 1991 (Solar Cycles 18 – 22). High-school students from Potsdam and Berlin digitized more than 3500 full-disk images during two- to three-week internships at AIP. The digital images cover a 15 cm $\times$ 15 cm region on photographic plates, which were scanned at a resolution of 7086 $\times$ 7086 pixels. The raw data are monochromatic 8-bit images in the Tagged Image File Format (TIFF). These images were calibrated and saved with improved photometric precision as 16-bit images with 2048 $\times$ 2048 pixels in the Flexible Image Transport System (FITS) format, which contains extensive headers describing the full-disk images and the observations. The various calibration steps include, for example, accurate measurements of the solar radius, determination of the limb-darkening function, and establishing an accurate coordinate system. The contrast-enhanced and limb-darkening corrected images as well as the raw data are freely available to researchers and the general public in publicly accessible repository. The data are published as a special data release of the Archives of Photographic PLates for Astronomical USE (APPLAUSE) project.
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P. Pal, M. Verma, J. Rendtel, et. al.
Thu, 30 Jul 20
-600/71
Comments: N/A
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http://arxiv.org/abs/2007.14410
Mergers can be detected as double-peak narrow emission line galaxies but they are difficult to disentangle from disc rotations and gas outflows. We aim to properly detect such galaxies and distinguish the underlying mechanisms. Relying on RCSED, we developed an automated selection procedure and found 5663 double-peak emission line galaxies at z<0.34 corresponding to 0.8% of the parent database. To characterise these galaxies, we built a single-peak no-bias control sample (NBCS) with the same redshift and stellar mass distributions as the double-peak sample (DPS). These two samples are indeed very similar in terms of absolute magnitude, [OIII] luminosity, colour-colour diagrams, age and specific star formation rate, metallicity, and environment. We find an important excess of S0 galaxies in the DPS, not observed in the NBCS, and which cannot be accounted for by the environment, as most of these galaxies are isolated or in poor groups. Similarly, we find a relative deficit of pure discs in the DPS late-type galaxies, that are preferentially of Sa type. In parallel, we observe a systematic central excess of star formation and extinction for DP galaxies. Finally, there are noticeable differences in the kinematics: the gas velocity dispersion is correlated with the galaxy inclination in the NBCS, whereas this relation does not hold for the DPS. Furthermore, the DP galaxies show larger stellar velocity dispersions and they deviate from the Tully-Fisher relation for both late-type and S0 galaxies. These discrepancies can be reconciled if one considers the two peaks as two different components. Considering the morphological biases in favour, bulge-dominated galaxies and star-formation central enhancement, we suggest a scenario of multiple sequential minor mergers driving the increase of the bulge size, leading to larger fractions of S0 galaxies and a deficit of pure disc galaxies.
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D. Maschmann, A. Melchior, G. Mamon, et. al.
Thu, 30 Jul 20
-599/71
Comments: 30 pages, 27 figures, article accepted to A&A
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Transient Jupiter Co-orbitals from Solar System Sources [EPA]
We demonstrate dynamical pathways from main-belt asteroid and Centaur orbits to those in co-orbital motion with Jupiter, including the retrograde (inclination $i>90^o$) state. We estimate that at any given time, there should be $\sim1$ kilometer-scale or larger escaped asteroid in a transient direct (prograde) orbit with semimajor axis near that of Jupiter’s ($a\simeq a_J$), with proportionally more smaller objects as determined by their size distribution. Most of these objects would be in the horseshoe dynamical state, which are hard to detect due to their moderate eccentricities (spending most of their time beyond 5 AU) and longitudes relative to Jupiter being spread nearly all over the sky. We also show that $\approx$1% of the transient asteroid co-orbital population is on retrograde orbits with Jupiter. This population, like the recently identified asteroid (514107) 2015 BZ$_{509}$, can spend millions of years with $a\simeq a_J$ including tens or hundreds of thousands of years formally in the retrograde 1:-1 co-orbital resonance. Escaping near-Earth asteroids (NEAs) are thus likely the precursors to the handful of known high-inclination objects with $a\simeq a_J$. We compare the production of jovian co-orbitals from escaping NEAs with those from incoming Centaurs. We find that temporary direct co-orbitals are likely dominated by Centaur capture, but we only find production of (temporary) retrograde jovian co-orbitals (including very long-lived ones) from the NEA source. We postulate that the primordial elimination of the inner Solar System’s planetesimal population could provide a supply route for a metastable outer Solar System reservoir for the high-inclination Centaurs.
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S. Greenstreet, B. Gladman and H. Ngo
Thu, 30 Jul 20
-598/71
Comments: Accepted at AJ
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Re-observing the NLS1 Galaxy RE J1034+396. II. New Insights on the Soft X-ray Excess, QPO and the Analogy with GRS 1915+105 [HEAP]
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http://arxiv.org/abs/2007.14704
RE J1034+396 displays the so far detected most significant X-ray Quasi-Periodic Oscillation (QPO) in AGN. We perform a detailed spectral-timing analysis on the data using recent simultaneous XMM-Newton, NuSTAR and Swift observations. We present the detailed energy dependence of the QPO’s frequency, rms, coherence and phase lag. We construct various frequency-resolved variability spectra, which are modelled together with the time-averaged spectra. Our study shows that four components are required to fit all the spectra, including an inner disc component (diskbb), two warm corona components (CompTT-1 and CompTT-2) and a hot corona component (nthComp). An important discovery is that within the two warm corona components, CompTT-2 (the hotter, less luminous component) contains the QPO signal, while the stochastic variability is concentrated in CompTT-1. These components also allow us to fit the lag-energy spectra, as well as being able to describe the previous observation of a strong QPO in 2007, and the absent QPO observations, by varying only the relative normalizations of these components. Our multi-wavelength study shows that the QPO’s detectability does not depend on the contemporaneous mass accretion rate through the outer disc as estimated from the UV flux. We do not detect a significant Iron K$\alpha$ line, nor any significant reflection component hump. Finally, we show that the rms and lag spectra of RE J1034+396 in the recent observation are very similar to the 67 Hz QPO in the micro-quasar GRS 1915+105. These new results reinforce the physical analogy between the two sources. We speculate that the QPO in both sources is due to expansion/contraction of the inner disc vertical structure.
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C. Jin, C. Done and M. Ward
Thu, 30 Jul 20
-597/71
Comments: 21 pages, 16 figures, 6 tables, submitted to MNRAS
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Gaia-DR2 extended kinematical maps. Part III: Rotation curves analysis, dark matter, and Modified Newtonian dynamics tests [GA]
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http://arxiv.org/abs/2007.14825
Recent statistical deconvolution methods have produced extended kinematical maps in a range of heliocentric distances that are a factor of two to three larger than those analysed in the Gaia Collaboration based on the same data. In this paper, we use such maps to derive the rotation curve both in the Galactic plane and in off-plane regions and to analyse the density distribution. By assuming stationary equilibrium and axisymmetry, we used the Jeans equation to derive the rotation curve. Then we fit it with density models that include both dark matter and predictions of the MOND (Modified Newtonian dynamics) theory. Since the Milky Way exhibits deviations from axisymmetry and equilibrium, we also considered corrections to the Jeans equation. To compute such corrections, we ran N-body experiments of mock disk galaxies where the departure from equilibrium becomes larger as a function of the distance from the centre. The rotation curve in the outer disk of the Milky Way that is constructed with the Jeans equation exhibits very low dependence on $R$ and $z$ and it is well-fitted both by dark matter halo and MOND models. The application of the Jeans equation for deriving the rotation curve, in the case of the systems that deviate from equilibrium and axisymmetry, introduces systematic errors that grow as a function of the amplitude of the average radial velocity. In the case of the Milky Way, we can observe that the amplitude of the radial velocity reaches $\sim 10\%$ that of the azimuthal one at $R\approx 20$ kpc. Based on this condition, using the rotation curve obtained from the Jeans equation to calculate the mass may overestimate its measurement.
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&. Chrobáková, M. López-Corredoira, F. Labini, et. al.
Thu, 30 Jul 20
-596/71
Comments: 11 pages, 8 figures, accepted to be published in A&A
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http://arxiv.org/abs/2007.14905
During their formation, emerging protoplanets tidally interact with their natal disks. Proto-gas-giant planets, with Hills radius larger than the disk thickness, open gaps and quench gas flow in the vicinity of their orbits. It is usually assumed that their type II migration is coupled to the viscous evolution of the disk. Although this hypothesis provides an explanation for the origin of close-in planets, it also encounter predicament on the retention of long-period orbits for most gas giant planets. Moreover, numerical simulations indicate that planets migrations are not solely determined by the viscous diffusion of their natal disk. Here we carry out a series of hydrodynamic simulations combined with analytic studies to examine the transition between different paradigms of type II migration. We find a range of planetary mass for which gas continues to flow through a severely depleted gap so that the surface density distribution in the disk region beyond the gap is maintained in a quasi-steady state. The associated gap profile modifies the location of corotation \& Lindblad resonances. In the proximity of the planet’s orbit, high-order Lindblad \& corotation torque are weakened by the gas depletion in the gap while low-order Lindblad torques near the gap walls preserves their magnitude. Consequently, the intrinsic surface density distribution of the disk determines delicately both pace and direction of planets’ type II migration. We show that this effect might stall the inward migration of giant planets and preserve them in disk regions where the surface density is steep.
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Y. Chen, X. Zhang, Y. Li, et. al.
Thu, 30 Jul 20
-595/71
Noise due to scattered light has been a frequent disturbance in the Advanced LIGO gravitational wave detectors, hindering the detection of gravitational waves. The non stationary scatter noise caused by low frequency motion can be recognized as arches in the time-frequency plane of the gravitational wave channel. In this paper, we characterize the scattering noise for LIGO’s third observing run O3 from April, 2024 to March, 2024. We find at least two different populations of scattering noise and we investigate the multiple origins of one of them as well as its mitigation. We find that relative motion between two specific surfaces is strongly correlated with the presence of scattered light and we implement a technique to reduce this motion. We also present an algorithm using a witness channel to identify the times this noise can be present in the detector.
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S. Soni, C. Austin, A. Effler, et. al.
Thu, 30 Jul 20
-594/71
Comments: 24 pages, 15 figures, 1 table
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Radio Echo in the Turbulent Corona and Simulations of Solar Drift-Pair Radio Bursts [SSA]
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http://arxiv.org/abs/2007.14648
Drift-pair bursts are an unusual type of solar low-frequency radio emission, which appear in the dynamic spectra as two parallel drifting bright stripes separated in time. Recent imaging spectroscopy observations allowed for the quantitative characterization of the drifting pairs in terms of source size, position, and evolution. Here, the drift-pair parameters are qualitatively analyzed and compared with the newly-developed Monte Carlo ray-tracing technique simulating radio-wave propagation in the inhomogeneous anisotropic turbulent solar corona. The results suggest that the drift-pair bursts can be formed due to a combination of the refraction and scattering processes, with the trailing component being the result of turbulent reflection (turbulent radio echo). The formation of drift-pair bursts requires an anisotropic scattering with the level of plasma density fluctuations comparable to that in type III bursts, but with a stronger anisotropy at the inner turbulence scale. The anisotropic radio-wave scattering model can quantitatively reproduce the key properties of drift-pair bursts: the apparent source size and its increase with time at a given frequency, the parallel motion of the source centroid positions, and the delay between the burst components. The trailing component is found to be virtually co-spatial and following the main component. The simulations suggest that the drift-pair bursts are likely to be observed closer to the disk center and below 100 MHz due to the effects of free-free absorption and scattering. The exciter of drift-pairs is consistent with propagating packets of whistlers, allowing for a fascinating way to diagnose the plasma turbulence and the radio emission mechanism.
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A. Kuznetsov, N. Chrysaphi, E. Kontar, et. al.
Thu, 30 Jul 20
-593/71
Comments: 13 pages, 7 figures
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X-ray Observations of a [C II]-bright, z=6.59 Quasar/Companion System [GA]
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http://arxiv.org/abs/2007.14571
We present deep Chandra observations of PSO J231.6576$-$20.8335, a quasar at redshift z=6.59 with a nearby (${\sim}8$ proper kpc) companion galaxy. ALMA observed both the quasar and companion to be bright in [C II], and the system has significant extended Ly$\alpha$ emission around the quasar, suggesting that a galaxy merger is ongoing. Unlike previous studies of two similar systems, and despite observing the system with Chandra for 140 ks, we do not detect the companion in X-rays. The quasar itself is detected, but only $13.3^{+4.8}{-3.7}$ net counts are observed. From a basic spectral analysis, the X-ray spectrum of the quasar is soft (hardness ratio of $\mathcal{HR} = -0.60{-0.27}^{+0.17}$, power-law index of $\Gamma=2.6^{+1.0}{-0.9}$), which results in a rest-frame X-ray luminosity comparable to other bright quasars ($L{2-10} = 1.09^{+2.20}{-0.70}\times 10^{45}\ \textrm{erg}\ \textrm{s}^{-1}$) despite the faint observed X-ray flux. We highlight two possible interpretations of this result: the quasar has a steep value of $\Gamma$ — potentially related to observed ongoing Eddington accretion — thereby pushing much of the emission out of our observed band, or the quasar has a more normal spectrum ($\Gamma{\sim}2$) but is therefore less X-ray luminous ($L{2-10} \sim 0.6 \times 10^{45}\ \textrm{ erg}\ \textrm{ s}^{-1}$).
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T. Connor, E. Bañados, C. Mazzucchelli, et. al.
Thu, 30 Jul 20
-592/71
Comments: 11 pages, 4 figures. Accepted for publication in ApJ
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An analytic model for OIII fine structure emission from high redshift galaxies [GA]
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http://arxiv.org/abs/2007.14439
Recent ALMA measurements have revealed bright OIII 88 micron line emission from galaxies during the Epoch of Reionization (EoR) at redshifts as large as $z \sim 9$. We introduce an analytic model to help interpret these and other upcoming OIII 88 micron measurements. Our approach sums over the emission from discrete Str$\ddot{\mathrm{o}}$mgren spheres and considers the total volume of ionized hydrogen in a galaxy of a given star-formation rate. We estimate the relative volume of doubly-ionized oxygen and ionized hydrogen and its dependence on the spectrum of ionizing photons. We then calculate the level populations of OIII ions in different fine-structure states for HII regions of specified parameters. In this simple model, a galaxy’s OIII 88 micron luminosity is determined by: the typical number density of free electrons in HII regions ($n_e$), the average metallicity of these regions ($Z$), the rate of hydrogen ionizing photons emitted ($Q_{\mathrm{HI}}$), and the shape of the ionizing spectrum. We cross-check our model by comparing it with detailed CLOUDY calculations, and find that it works to better than 15$\%$ accuracy across a broad range of parameter space. Applying our model to existing ALMA data at $z \sim 6-9$, we derive lower bounds on the gas metallicity and upper bounds on the gas density in the HII regions of these galaxies. These limits vary considerably from galaxy to galaxy, with the tightest bounds indicating $Z \gtrsim 0.5 Z_\odot$ and $n_{\mathrm{H}} \lesssim 50$ cm$^{-3}$ at $2-\sigma$ confidence.
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S. Yang and A. Lidz
Thu, 30 Jul 20
-591/71
Comments: N/A
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http://arxiv.org/abs/2007.14962
Future precision cosmology from large-scale structure experiments including the Dark Energy Spectroscopic Instrument (DESI) and Euclid will probe wider and deeper cosmic volumes than those covered by previous surveys. The Cartesian power spectrum analysis of anisotropic galaxy clustering based on the Fourier plane wave basis makes a number of assumptions, including the local plane-parallel approximation, that will no longer be valid on very large scales and may degrade cosmological constraints. We propose an approach that utilises a hybrid basis: on the largest scales, clustering statistics are decomposed into spherical Fourier modes which respect the natural geometry of both survey observations and physical effects along the line of sight, such as redshift-space distortions, the Alcock–Paczy\’nsky and light-cone effects; on smaller scales with far more clustering modes, we retain the computational benefit of the power spectrum analysis aided by fast Fourier transforms. This approach is particularly suited to the likelihood analysis of local primordial non-Gaussianity $f_\textrm{NL}$ through the scale-dependent halo bias, and we demonstrate its applicability with $N$-body simulations. We also release our public code Harmonia (http://github.com/MikeSWang/Harmonia) for galaxy clustering likelihood inference in spherical Fourier or hybrid-basis analyses.
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M. Wang, S. Avila, D. Bianchi, et. al.
Thu, 30 Jul 20
-590/71
Comments: submitted to JCAP, 39 pages, 12 figures and 1 table; public code available at this http URL
The frequent detection of binary mergers of $\sim 30 M_{\odot}$ black holes (BHs) by the Laser Interferometer Gravitational-Wave Observatory (LIGO) rekindled researchers’ interest in primordial BHs (PBHs) being dark matter (DM). In this work, we looked at PBHs distributed as DM with a monochromatic mass of $30 M_{\odot}$ and examined the encounter-capture scenario of binary formation, where the densest central region of DM halo dominates. Thus, we paid special attention to the tidal effect by the supermassive black hole (SMBH) present. In doing so, we discovered a necessary tool called loss zone that complements the usage of loss cone. We found that the tidal effect is not prominent in affecting binary formation, which also turned out insufficient in explaining the totality of LIGO’s event rate estimation, especially due to a microlensing event constraining the DM fraction in PBH at the mass of interest from near unity to an order smaller. Meanwhile, early-universe binary formation scenario proves so prevailing that the LIGO signal in turn constrains the PBH fraction below one percent. Thus, people should put more faith in alternative PBH windows and other DM candidates.
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Y. Gao, X. Zhang and M. Su
Thu, 30 Jul 20
-589/71
Comments: N/A
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maxsmooth: Rapid maximally smooth function fitting with applications in Global 21-cm cosmology [CEA]
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http://arxiv.org/abs/2007.14970
Maximally Smooth Functions (MSFs) are a form of constrained functions in which there are no inflection points or zero crossings in high order derivatives. Consequently, they have applications to signal recovery in experiments where signals of interest are expected to be non-smooth features masked by larger smooth signals or foregrounds. They can also act as a powerful tool for diagnosing the presence of systematics. However, the constrained nature of MSFs makes fitting these functions a non-trivial task. Here, we introduce maxsmooth, an open source package that uses quadratic programming to rapidly fit MSFs. We demonstrate the efficiency and reliability of maxsmooth by comparison to commonly used fitting routines. We show that by using quadratic programming we can reduce the fitting time by approximately two orders of magnitude. maxsmooth features a built-in library of MSF models and allows the user to define their own. We also introduce and implement with maxsmooth Partially Smooth Functions, which are useful for describing elements of non-smooth structure in foregrounds. This work has been motivated by the problem of foreground modelling in 21-cm cosmology for which MSFs have been shown to be a viable alternative to polynomial models. We discuss applications of maxsmooth to 21-cm cosmology and highlight this with examples using data from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) and the Large-aperture Experiment to Detect the Dark Ages (LEDA) experiments. MSFs are applied to data from LEDA for the first time in this paper. maxsmooth is pip installable and available for download at: http://github.com/htjb/maxsmooth
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H. Bevins, W. Handley, A. Fialkov, et. al.
Thu, 30 Jul 20
-588/71
Comments: 19 pages, 15 figures
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Evolution of the universe during the inflationary epoch [CL]
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http://arxiv.org/abs/2007.13165
We often find in the literature solutions to the Friedmann and fluid equations for simple cosmological models during the matter, radiation or cosmological constant dominated epochs. However no solutions appear for the inflationary era dominated by the potential energy of a scalar field due, perhaps, to the fact that we do not have as yet a strongly favored model of inflation; there are, of course, very well motivated models which fit the data. The purpose of this article is to study with some detail the evolution of the Universe during inflation in the slow-roll approximation. Taking the Starobinsky model as an example, we display exact solutions for the time evolution of the scalar field $\phi(t)$, scale factor $a(t)$, Hubble function $H(t)$, equation of state parameter $\omega(t)$ and acceleration of the scale factor $\ddot{a}(t)$ among other quantities of interest.
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G. German
Thu, 30 Jul 20
-587/71
Comments: 14 pages, 13 figures
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