adsabs/SciX_UAT_keywords huggingface dataset:
Dissipative Dark Substructure: The Consequences of Atomic Dark Matter on Milky Way Analog Subhalos

Using cosmological hydrodynamical zoom-in simulations, we explore the properties of subhalos in Milky Way analogs that contain a subcomponent of atomic dark matter (ADM). ADM differs from cold dark matter (CDM) due to the presence of self-interactions that lead to energy dissipation, analogous to standard model baryons. This model can arise in dark sectors that are natural and theoretically motivated extensions to the standard model. The simulations used in this work were carried out using GIZMO and utilize the FIRE-2 galaxy formation physics in the standard model baryonic sector. For the parameter points we consider, the ADM gas cools efficiently, allowing it to collapse to the center of subhalos. This increases a subhalo's central density and affects its orbit, with more subhalos surviving small pericentric passages. The subset of subhalos that host satellite galaxies have cuspier density profiles and smaller stellar half-mass radii relative to CDM. The entire population of dwarf galaxies produced in the ADM simulations is more compact than those seen in CDM simulations, unable to reproduce the entire diversity of observed dwarf galaxy structures. Additionally, we also identify a population of highly compact subhalos that consist nearly entirely of ADM and form in the central region of the host, where they can leave distinctive imprints in the baryonic disk. This work presents the first detailed exploration of subhalo properties in a strongly dissipative dark matter scenario, providing intuition for how other regions of ADM parameter space, as well as other dark sector models, would impact galactic-scale observables.

Keywords: dark matter; n-body simulations; dark matter distribution; hydrodynamical simulations; dwarf galaxies
Flybys, Orbits, Splashback: Subhalos and the Importance of the Halo Boundary

The classification of dark matter halos as isolated hosts or subhalos is critical for our understanding of structure formation and the galaxy-halo connection. Most commonly, subhalos are defined to reside inside a spherical overdensity boundary such as the virial radius. The resulting host-subhalo relations depend sensitively on the somewhat arbitrary overdensity threshold, but the impact of this dependence is rarely quantified. The recently proposed splashback radius tends to be larger and to include more subhalos than even the largest spherical overdensity boundaries. We systematically investigate the dependence of the subhalo fraction on the radius definition and show that it can vary by factors of unity between different spherical overdensity definitions. Using splashback radii can yet double the abundance of subhalos compared to the virial definition. We also quantify the abundance of flyby (or backsplash) halos, hosts that used to be subhalos in the past. We show that the majority of these objects are mislabeled satellites that are naturally classified as subhalos when we use the splashback radius. We show that the subhalo fraction can be understood as a universal function of only peak height and the slope of the linear power spectrum. We provide a simple fitting function that captures our simulation results to 20% accuracy across a wide range of halo masses, redshifts, and cosmologies. Finally, we demonstrate that splashback radii significantly change our understanding of satellite and flyby galaxies in the Local Group.

Keywords: large-scale structure of the universe; cold dark matter
[C II] and CO Emission along the Bar and Counter-arms of NGC 7479

We present new SOFIA [C II] and ALMA COJ=1→0 observations of the nearby asymmetric barred spiral galaxy NGC 7479. The data, which cover the whole bar of the galaxy and the counter-arms visible in the radio continuum, are analyzed in conjunction with a wealth of existing visible, infrared, radio, and X-ray data. As in most normal galaxies, the [C II] emission is generally consistent with emission from cooling gas excited by photoelectric heating in photodissociation regions. However, anomalously high [C II]/CO ratios are seen at the two ends of the counter-arms. Both ends show shell-like structures, possibly bubbles, in Hα emission. In addition, the southern end has [C II]-to-infrared emission ratios inconsistent with normal star formation. Because there is little H I emission at this location, the [C II] emission probably originates in warm shocked molecular gas heated by the interaction of the radio jet forming the counter-arms with the interstellar medium in the galaxy. At two other locations, the high [C II]/CO ratios provide evidence for the existence of patches of CO-dark molecular gas. The [C II] and CO observations also reveal resolved velocity components along the bar. In particular, the CO emission can be separated into two components associated with gas along the leading edge of the bar and gas trailing the bar. The trailing gas component that amounts to approximately 40% of the gas around the bar region may be related to a minor merger. * Based on SOFIA observations with FIFI-LS.

Keywords: barred spiral galaxies; infrared galaxies; molecular gas
Measuring the Speed of Light with Updated Hubble Diagram of High-redshift Standard Candles

The possible time variation of the fundamental constants of nature has been an active subject of research in modern physics. In this paper, we propose a new method to investigate such possible time variation of the speed of light c using the updated Hubble diagram of high-redshift standard candles including Type Ia Supernovae (SNe Ia) and high-redshift quasars (based on UV-X relation). Our findings show that the SNe Ia Pantheon sample, combined with currently available sample of cosmic chronometers, would produce robust constraints on the speed of light at the level of c/c 0 = 1.03 ± 0.03. For the Hubble diagram of UV+X-ray quasars acting as a new type of standard candle, we obtain c/c 0 = 1.19 ± 0.07. Therefore, our results confirm that there is no strong evidence for deviation from a constant speed of light up to z ~ 2. Moreover, we discuss how our technique might be improved at much higher redshifts (z ~ 5), focusing on future measurements of the acceleration parameter X(z) with gravitational waves (GWs) produced by binary neutron star mergers. In particular, in the framework of the second-generation space-based GW detector, DECi-hertz Interferometer Gravitational Wave Observatory, the speed of light is expected to be constrained with a precision of Δc/c = 10-3.

Keywords: quasars; type ia supernovae; gravitational waves; cosmological parameters
Lanthanide Features in Near-infrared Spectra of Kilonovae

The observations of GW170817/AT2017gfo have provided us with evidence that binary neutron star mergers are sites of r-process nucleosynthesis. However, the observed signatures in the spectra of GW170817/AT2017gfo have not been fully decoded, especially in the near-infrared (NIR) wavelengths. In this paper, we investigate the kilonova spectra over the entire wavelength range with the aim of elemental identification. We systematically calculate the strength of bound-bound transitions by constructing a hybrid line list that is accurate for important strong transitions and complete for weak transitions. We find that the elements on the left side of the periodic table, such as Ca, Sr, Y, Zr, Ba, La, and Ce, tend to produce prominent absorption lines in the spectra. This is because such elements have a small number of valence electrons and low-lying energy levels, resulting in strong transitions. By performing self-consistent radiative transfer simulations for the entire ejecta, we find that La III and Ce III appear in the NIR spectra, which can explain the absorption features at λ ~ 12000-14000 Å in the spectra of GW170817/AT2017gfo. The mass fractions of La and Ce are estimated to be >2 × 10-6 and ~(1-100) × 10-5, respectively. An actinide element Th can also be a source of absorption as the atomic structure is analogous to that of Ce. However, we show that Th III features are less prominent in the spectra because of the denser energy levels of actinides compared to those of lanthanides.

Keywords: r-process; neutron stars; radiative transfer simulations; atomic physics
Oumuamuas Passing through Molecular Clouds

The detections of 1I/'Oumuamua and 2I/Borisov within just two years of each other impressively demonstrate that interstellar objects (ISOs) must be common in the Milky Way. Once released from their parent system, these ISOs travel for billions of years through interstellar space. While often imagined as empty, interstellar space contains gas and dust most prominent in the form of molecular clouds. Performing numerical simulations, we test how often ISOs cross such molecular clouds (MCs). We find that the ISOs pass through MCs amazingly often. In the solar neighborhood, ISOs typically spend 0.1%-0.2% of their journey inside MCs, for relatively slow ISOs (<5 km s-1) this can increase to 1%-2%, equivalent to 10-20 Myr per Gyr. Thus the dynamically youngest ISOs spend the longest time in MCs. In other words, MCs must mainly contain relatively young ISOs (<1-2 Gyr). Thus the half-life of the seeding process by ISOs is substantially shorter than a stellar lifetime. The actual amount of time spent in MCs decreases with distance to the Galactic center. We find that ISOs pass through MCs so often that backtracing their path to find their parent star beyond 250 Myr seems pointless. Besides, we give a first estimate of the ISO density depending on the distance to the Galactic center based on the stellar distribution.

Keywords: giant molecular clouds; oort cloud objects; free floating planets
Material Properties of Organic Liquids, Ices, and Hazes on Titan

Titan has a diverse range of materials in its atmosphere and on its surface: the simple organics that reside in various phases (gas, liquid, and ice) and the solid complex refractory organics that form Titan's haze layers. These materials all actively participate in various physical processes on Titan, and many material properties are found to be important in shaping these processes. Future in situ explorations on Titan would likely encounter a range of materials, and a comprehensive database to archive the material properties of all possible material candidates will be needed. Here, we summarize several important material properties of the organic liquids, ices, and the refractory hazes on Titan that are available in the literature and/or that we have computed. These properties include thermodynamic properties (phase-change points, sublimation and vaporization saturation vapor pressure, and latent heat), and physical properties (organic liquid densities and organic ice and haze densities). We have developed a new database to provide a repository for these data and make them available to the science community. These data can be used as inputs for various theoretical models to interpret current and future remote sensing and in situ atmospheric and surface measurements on Titan. The material properties of the simple organics may also be applicable to giant planets and icy bodies in the outer solar system, interstellar medium, protoplanetary disks, and exoplanets.

Keywords: titan; saturnian satellites; planetary atmospheres; dwarf planets; natural satellites (solar system); surface ices; planetary surfaces; interstellar medium; protoplanetary disks; exoplanets
Characterizing X-Ray Properties of the Gamma-Ray Pulsar PSR J1418-6058 in the Rabbit Pulsar Wind Nebula

We report on X-ray studies of the gamma-ray pulsar PSR J1418-6058 in the Rabbit pulsar wind nebula (PWN) carried out using archival Chandra and XMM-Newton observations. A refined timing analysis performed with the 120 ks XMM-Newton data finds significant (p ≈ 10-7) pulsation at P ≈ 110 ms which is consistent with that measured with the Fermi Large Area Telescope (LAT). In the Chandra image, we find extended emission around the pulsar similar to those seen around other pulsars in young PWNe, which further argues association between PSR J1418-6058 and the Rabbit PWN. The X-ray spectrum of the pulsar is hard and similar to those of soft-gamma pulsars. Hence PSR J1418-6058 may add to the list of soft-gamma pulsars.

Keywords: pulsars; neutron stars; x-ray sources; stellar winds
Physical Conditions in Shocked Interstellar Gas Interacting with the Supernova Remnant IC 443

We present the results of a detailed investigation into the physical conditions in interstellar material interacting with the supernova remnant (SNR) IC 443. Our analysis is based on a comprehensive examination of high-resolution far-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope of two stars behind IC 443. One of our targets (HD 43582) probes gas along the entire line of sight through the SNR, while the other (HD 254755) samples material located ahead of the primary supernova shock front. We identify low-velocity quiescent gas in both directions and find that the densities and temperatures in these components are typical of diffuse atomic and molecular clouds. Numerous high-velocity components are observed in the absorption profiles of neutral and singly ionized atomic species toward HD 43582. These components exhibit a combination of greatly enhanced thermal pressures and significantly reduced dust-grain depletions. We interpret this material as cooling gas in a recombination zone far downstream from shocks driven into neutral gas clumps. The pressures derived for a group of ionized gas components at high positive velocity toward HD 43582 are lower than those of the other shocked components, pointing to pressure inhomogeneities across the remnant. A strong, very high velocity component near -620 km s-1 is seen in the absorption profiles of highly ionized species toward HD 43582. The velocity of this material is consistent with the range of shock velocities implied by observations of soft thermal X-ray emission from IC 443. Moderately high velocity gas toward HD 254755 may represent shocked material from a separate foreground SNR. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Keywords: interstellar abundances; interstellar molecules; supernova remnants; diffuse interstellar clouds
Simulations of the Progenitors of Black Hole-Neutron Star Gravitational Wave Sources

Recent discoveries of gravitational wave (GW) events most likely originating from black hole (BH) + neutron star (NS) mergers reveal the existence of BH+NS binaries. The formation of BH+NS binaries and their merger rates through isolated binary evolution have been investigated extensively with population synthesis simulations. A detailed stellar evolution modeling of the formation of this population, however, is missing from the literature. In this work, we create the first complete 1D model of more than 30 BH+NS progenitor systems, which are calculated self-consistently until collapse of the iron core with infall velocity exceeding 1000 km s-1. Focusing on the progenitors of BH-NS GW sources, we apply the MESA code starting from a post-common-envelope binary with short orbital period (<1 day) consisting of a BH and a zero-age main-sequence helium star that experiences stable mass transfer. The (ultra)stripped supernova explosion is subsequently modeled using a semianalytic method to reveal final remnant masses and momentum kicks. Three example systems (A, B, and C) eventually evolve into BH+NS binaries with component masses of (M BH, M NS) = (8.80, 1.53), (8.92, 1.45), and (5.71, 1.34) M ⊙, respectively. These NS masses could be significantly larger depending on the exact mass cut during the supernova explosion. These BH+NS systems are likely to merge and produce GW events within a Hubble time. System C is a potential progenitor of a GW200115-like event, while Systems A and B are possible candidates for a GW200105-like event and may represent the final destiny of the X-ray binary SS 433.

Keywords: black holes; neutron stars; gravitational wave sources; x-ray binary stars; stellar evolution
The Rotation Curve, Mass Distribution, and Dark Matter Content of the Milky Way from Classical Cepheids

With the increasing number of large stellar survey projects, the quality and quantity of excellent tracers for studying the Milky Way are rapidly growing, one of which is the classical Cepheids. Classical Cepheids are high-precision standard candles with very low typical uncertainties (<3%) available via the mid-infrared period-luminosity relation. About 3500 classical Cepheids identified from the Optical Gravitational Lensing Experiment, All-Sky Automated Survey for Supernova, Gaia, Wide-field Infrared Survey Explorer, and Zwicky Transient Facility survey data have been analyzed in this work, and their spatial distributions show a clear signature of Galactic warp. Two kinematical methods are adopted to measure the Galactic rotation curve (RC) in the Galactocentric distance range of $4\lesssim {R}_{\mathrm{GC}}\lesssim 19\,\mathrm{kpc}$ . Gently declining RCs are derived by both the proper motion (PM) method and three-dimensional velocity vector (3DV) method. The largest sample of classical Cepheids with the most accurate 6D phase-space coordinates available to date are modeled in the 3DV method, and the resulting RC is found to decline at the relatively smaller gradient of (-1.33 ± 0.1) $\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{kpc}}^{-1}$ . Comparing to results from the PM method, a higher rotation velocity ((232.5 ± 0.83) $\mathrm{km}\,{{\rm{s}}}^{-1}$ ) is derived at the position of the Sun in the 3DV method. The virial mass and local dark matter density are estimated from the 3DV method, which is the more reliable method, ${M}_{\mathrm{vir}}=(0.822\pm 0.052)\times {10}^{12}\,{M}_{\odot }$ and ${\rho }_{\mathrm{DM},\odot }=0.33\pm 0.03$ GeV, respectively.

Keywords: dark matter density; galaxy mass distribution; milky way dark matter halo; milky way dynamics; cepheid variable stars; galaxy rotation curves; dark matter
X-Ray Quasi-periodic Oscillations in the Lense-Thirring Precession Model. II. Variability of the Relativistic Iron Kα Line

The reprocessing of primary X-ray emission in the accretion disk of black hole X-ray binaries (BHXRBs) produces a reflection spectrum with the characteristic Fe Kα fluorescence line. Strong low-frequency quasi-periodic oscillations (QPOs) are observed from BHXRBs, and the dependence of QPO properties (e.g., phase lag) on the inclination angle suggests that the observed QPO may be associated with a geometrical effect, e.g., the precession of the X-ray source due to frame dragging near the spinning black hole. Here, in the scenario of the Lense-Thirring precession of the X-ray source, we use a Monte Carlo simulation of radiative transfer to study the irradiation/reflection and the resultant spectral properties including the Fe Kα line as a function of precession phase (time). We found that the reflection fraction, I.e., the ratio of incident flux toward the disk and the direct flux toward the observer at infinity, is modulated by the precession phase, which depends on the truncation radius (I.e., the spectral state in the truncated disk model) and the inclination angle. The Fe Kα line profile also changes as the primary X-ray source precesses, with the line luminosity and the flux-weighted centroid energy varying with the precession phase. The periodically modulated 2-10 keV continuum flux could apparently lag the line luminosity in phase, if the truncation radius is small enough for Doppler effects due to disk orbital motion to significantly affect the observed radiation.

Keywords: accretion; black hole physics
Distribution of Hα Emitters in Merging Galaxy Clusters

Studies of star formation in various galaxy cluster mergers have reached apparently contradictory conclusions regarding whether mergers stimulate star formation, quench it, or have no effect. Because the mergers studied span a range of time since pericenter (TSP), it is possible that the apparent effect on star formation is a function of the TSP. We use a sample of 12 bimodal mergers to assess the star formation as a function of TSP. We measure the equivalent width of the Hα emission line in ~100 member galaxies in each merger, classify galaxies as emitters or nonemitters, and then classify emitters as star-forming galaxies (SFGs) or active galactic nucleus (AGN) based on the [N II] λ6583 line. We quantify the distribution of SFG and AGN relative to nonemitters along the spatial axis defined by the subcluster separation. The SFG and AGN fractions vary from merger to merger but show no trend with TSP. The spatial distribution of SFG is consistent with that of nonemitters in eight mergers, but show significant avoidance of the system center in the remaining four mergers, including the three with the lowest TSP. If there is a connection between star formation activity and TSP, probing it further will require more precise TSP estimates and more mergers with TSP in the range of 0-400 Myr.

Keywords: galaxy clusters; star formation
Black Hole Activity Imprints on the Internal Plateau and the Subsequent Sharp Decay

A stellar-mass black hole (BH) or a millisecond magnetar is believed to be born as the central engine of gamma-ray bursts (GRBs). The presence of plateaus in the X-ray extended emission or afterglow of GRBs is widely accepted as an indicator of a magnetar central engine, particularly those with a sharp decay (faster than t ‑3), the so-called internal plateau. However, an alternative model, by taking the evolution of the magnetic flux at the BH horizon into account, suggests that an internal plateau can also arise from a jet powered by the Blandford–Znajek (BZ) mechanism (hereafter, a BZ jet). In this study, we propose that a precessional BZ jet would manifest a quasiperiodic oscillation (QPO) signature on the internal plateau and the subsequent sharp decay. Such lightcurves cannot be readily explained by the activity of a short-lived, supermassive magnetar, thus favoring a Kerr BH as the central engine. The X-ray afterglow of GRB 050904, comprising nine flares, is characterized by a QPO-modulated plateau and sharp decay, which can be well reproduced by a precessional BZ jet model. Therefore, one potential clue for distinguishing between these two engines lies in whether the QPO signature is present throughout the entire plateau and the subsequent sharp decay, as the magnetar scenario suggests a collapse at the end of the plateau.

Keywords: gamma-ray bursts; black hole physics; stellar accretion disks; relativistic jets