adsabs/SciX_UAT_keywords huggingface dataset:
A Population of Luminous Globular Clusters and Stripped Nuclei with Elevated Mass to Light Ratios around NGC 5128

The dense central regions of tidally disrupted galaxies can survive as ultracompact dwarfs (UCDs) that hide among the luminous globular clusters (GCs) in the halo of massive galaxies. An exciting confirmation of this model is the detection of overmassive black holes in the centers of some UCDs, which also lead to elevated dynamical mass-to-light ratios (M/L dyn). Here we present new high-resolution spectroscopic observations of 321 luminous GC candidates in the massive galaxy NGC 5128/Centaurus A. Using these data we confirm 27 new luminous GCs, and measure velocity dispersions for 57 luminous GCs (with g-band luminosities between 2.5 × 105 and 2.5 × 107 L ⊙), of which 48 are new measurements. Combining these data with size measurements from Gaia, we determine the M/L dyn for all 57 luminous GCs. We see a clear bimodality in the M/L dyn distribution, with a population of normal GCs with mean M/L dyn = 1.51 ± 0.31, and a second population of ~20 GCs with elevated mean M/L dyn = 2.68 ± 0.22. We show that black holes with masses ~4%-18% of the luminous GCs can explain the elevated mass-to-light ratios. Hence, it is plausible that the NGC 5128 sources with elevated M/L dyn are mostly stripped galaxy nuclei that contain massive central black holes, though future high spatial resolution observations are necessary to confirm this hypothesis for individual sources. We also present a detailed discussion of an extreme outlier, VHH81-01, one of the largest and most massive GC in NGC 5128, making it an exceptionally strong candidate to be a tidally stripped nucleus. * This paper includes data gathered with the 6.5 m Magellan Telescope at Las Campanas Observatory, Chile.

Keywords: ultracompact dwarf galaxies; globular star clusters; mass-to-light ratio; galaxy nuclei; stellar kinematics; stellar dynamics
A Self-gravity Module for the PLUTO Code

We present a novel implementation of an iterative solver for the solution of Poisson's equation in the PLUTO code for astrophysical fluid dynamics. Our solver relies on a relaxation method in which convergence is sought as the steady-state solution of a parabolic equation, whose time discretization is governed by the Runge-Kutta-Legendre (RKL) method. Our findings indicate that the RKL-based Poisson solver, which is both fully parallel and rapidly convergent, has the potential to serve as a practical alternative to conventional iterative solvers such as the Gauss-Seidel and successive overrelaxation methods. Additionally, it can mitigate some of the drawbacks of these traditional techniques. We incorporate our algorithm into a multigrid solver to provide a simple and efficient gravity solver that can be used to obtain the gravitational potentials in self-gravitational hydrodynamics. We test our implementation against a broad range of standard self-gravitating astrophysical problems designed to examine different aspects of the code. We demonstrate that the results match excellently with analytical predictions (when available), and the findings of similar previous studies.

Keywords: computational methods; gravitation; hydrodynamical simulations
Branching Ratio for O + H3 + Forming OH+ + H2 and H2O+ + H

The gas-phase reaction of ${\rm{O}}+{{\rm{H}}}_{3}^{+}$ has two exothermic product channels: OH+ + H2 and H2O+ + H. In the present study, we analyze experimental data from a merged-beams measurement to derive thermal rate coefficients resolved by product channel for the temperature range from 10 to 1000 K. Published astrochemical models either ignore the second product channel or apply a temperature-independent branching ratio of 70% versus 30% for the formation of OH+ + H2 versus H2O+ + H, respectively, which originates from a single experimental data point measured at 295 K. Our results are consistent with this data point, but show a branching ratio that varies with temperature reaching 58% versus 42% at 10 K. We provide recommended rate coefficients for the two product channels for two cases, one where the initial fine-structure population of the O(3 P J ) reactant is in its J = 2 ground state and the other one where it is in thermal equilibrium.

Keywords: interstellar molecules; molecular clouds; molecule destruction; molecule formation
The Upper Atmosphere of Uranus from Stellar Occultations. I. Methods and Validation

Measurements made by the Voyager 2 spacecraft during its flybys of Uranus in 1986 found warm stratospheric and hot thermospheric temperatures that cannot be explained by solar energy alone. It contributes to what has become known as the "giant planet energy crisis"; there is a fundamental lack of understanding of the energy balance of giant planets in the solar system. Uranus, in particular, has both the hottest thermospheric temperatures and the weakest internal heat flux of all four giant planets. Moreover, the Voyager 2 UV temperature measurements are at odds with the many contemporaneous Earth-based stellar occultation observations. In this work, we examine the 1977 Uranus stellar occultation (U0) and compare the observed light curve to reported Voyager 2 temperature profiles by simulating the latter into stellar occultation light curves. In this investigation, we find that the observed light curves are in tension with the simulated light curves to a high degree of statistical confidence. Next, we reprocess the U0 light curves using a modern approach, with some significant adjustments described herein, and report updated profiles. We find that the lower thermosphere of Uranus is much cooler than the Voyager 2 profiles suggest but slightly warmer than those originally published from the U0 occultation. In Paper II, we will present the results of applying these methods to many of the dozens of archival Uranus stellar occultations.

Keywords: uranus; stellar occultation; planetary atmospheres; stratosphere; thermosphere
Hot Gas Outflow Properties of the Starburst Galaxy NGC 4945

We analyze 330 ks of Chandra X-ray imaging and spectra of the nearby, edge-on starburst and Seyfert type 2 galaxy NGC 4945 to measure the hot gas properties along the galactic outflows. We extract and model spectra from 15 regions extending from ‑0.55 to +0.85 kpc above and below the galactic disk to determine the best-fit parameters and metal abundances. We find that the hot gas temperatures and number densities peak in the central regions and decrease along the outflows. These profiles are inconsistent with a spherical, adiabatically expanding wind model, suggesting the need to include mass loading and/or a nonspherical outflow geometry. We estimate the mass outflow rate of the hot wind to be 1.6 M ⊙ yr‑1. Emission from charge exchange is detected in the northern outflow, and we estimate it contributes 12% to the emitted, broadband (0.5–7 keV) X-ray flux.

Keywords: galactic winds; starburst galaxies
The Role of Clouds on the Depletion of Methane and Water Dominance in the Transmission Spectra of Irradiated Exoplanets

Observations suggest an abundance of water and a paucity of methane in the majority of observed exoplanetary atmospheres. We isolate the effect of atmospheric processes to investigate possible causes. Previously, we studied the effect of effective temperature, surface gravity, metallicity, carbon-to-oxygen ratio, and stellar type assuming cloud-free thermochemical equilibrium and disequilibrium chemistry. However, under these assumptions, methane remains a persisting spectral feature in the transmission spectra of exoplanets over a certain parameter space, the Methane Valley. In this work, we investigate the role of clouds on this domain and we find that clouds change the spectral appearance of methane in two direct ways: (1) by heating up the photosphere of colder planets and (2) by obscuring molecular features. The presence of clouds also affects methane features indirectly: (1) cloud heating results in more evaporation of condensates and hence releases additional oxygen, causing water-dominated spectra of colder carbon-poor exoplanets, and (2) HCN/CO production results in a suppression of depleted methane features by these molecules. The presence of HCN/CO and a lack of methane could be an indication of cloud formation on hot exoplanets. Cloud heating can also deplete ammonia. Therefore, a simultaneous depletion of methane and ammonia is not unique to photochemical processes. We propose that the best targets for methane detection are likely to be massive but smaller planets with a temperature around 1450 K orbiting colder stars. We also construct Spitzer synthetic color maps and find that clouds can explain some of the high-contrast observations by IRAC's channel 1 and 2.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition
Discovery of Asymmetric Spike-like Structures of the 10 au Disk around the Very Low-luminosity Protostar Embedded in the Taurus Dense Core MC 27/L1521F with ALMA

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations have revealed an increasing number of compact protostellar disks with radii of less than a few tens of astronomical units and that young Class 0/I objects have an intrinsic size diversity. To deepen our understanding of the origin of such tiny disks, we have performed highest-resolution configuration observations with ALMA at a beam size of ∼0.″03 (4 au) on the very low-luminosity Class 0 protostar embedded in the Taurus dense core MC 27/L1521F. The 1.3 mm continuum measurement successfully resolved a tiny, faint (∼1 mJy) disk with a major axis length of ∼10 au, one of the smallest examples in the ALMA protostellar studies. In addition, we detected spike-like components in the northeastern direction at the disk edge. Gravitational instability or other fragmentation mechanisms cannot explain the structures, given the central stellar mass of ∼0.2 M ⊙ and the disk mass of ≳10‑4 M ⊙. Instead, we propose that these small spike structures were formed by a recent dynamic magnetic flux transport event due to interchange instability that would be favorable to occur if the parental core has a strong magnetic field. The presence of complex arc-like structures on a larger (∼2000 au) scale in the same direction as the spike structures suggests that the event was not single. Such episodic, dynamical events may play an important role in maintaining the compact nature of the protostellar disk in the complex gas envelope during the main accretion phase.

Keywords: star formation; protostars; molecular clouds; interstellar medium; circumstellar envelopes; magnetic fields
Spectroscopic Confirmation of Two Extremely Massive Protoclusters, BOSS1244 and BOSS1542, at z = 2.24

We present spectroscopic confirmation of two new massive galaxy protoclusters at z = 2.24 ± 0.02, BOSS1244 and BOSS1542, traced by groups of Coherently Strong Lyα Absorption (CoSLA) systems imprinted in the absorption spectra of a number of quasars from the Sloan Digital Sky Survey III (SDSS III) and identified as overdensities of narrowband-selected Hα emitters (HAEs). Using Multiple Mirror Telescope/Magellan Infrared Spectrograph and Large Binocular Telescope/LUCI near-infrared (NIR) spectroscopy, we confirm 46 and 36 HAEs in the BOSS1244 (~55 arcmin2) and BOSS1542 (~61 arcmin2) fields, respectively. BOSS1244 displays a southwest (SW) component at z = 2.230 ± 0.002 and another northeast (NE) component at z = 2.246 ± 0.001 with the line-of-sight velocity dispersions of 405 ± 202 km s-1 and 377 ± 99 km s-1, respectively. Interestingly, we find that the SW region of BOSS1244 contains two substructures in redshift space, likely merging to form a larger system. In contrast, BOSS1542 exhibits an extended filamentary structure with a low-velocity dispersion of 247 ± 32 km s-1 at z = 2.241 ± 0.001, providing a direct confirmation of a large-scale cosmic web in the early universe. The galaxy overdensities δg on the scale of 15 cMpc are 22.9 ± 4.9, 10.9 ± 2.5, and 20.5 ± 3.9 for the BOSS1244 SW, BOSS1244 NE, and BOSS1542 filament, respectively. They are the most overdense galaxy protoclusters (δg > 20) discovered to date at z > 2. These systems are expected to become virialized at z ~ 0 with a total mass of MSW = (1.59 ± 0.20) × 1015M⊙, MNE = (0.83 ± 0.11) × 1015 M⊙ and Mfilament = (1.42 ± 0.18) × 1015 M⊙, respectively. Our results suggest that the dense substructures of BOSS1244 and BOSS1542 will eventually evolve into the Coma-type galaxy clusters or even larger. Together with BOSS1441 described in Cai et al., these extremely massive overdensities at z = 2-3 exhibit different morphologies, indicating that they are in different assembly stages in the formation of early galaxy clusters. Furthermore, there are two quasar pairs in BOSS1441 and one quasar pair in BOSS1244 and BOSS1542; CoSLAs detected in these quasar pairs can be used to trace the extremely massive large-scale structures of the universe.

Keywords: protoclusters; large-scale structure of the universe; high-redshift galaxies; galaxy evolution; galaxy formation
A Possible Correlation between Metallicity and Near-IR Color for Late-M and L Dwarfs

We examine the relationship between metallicity and J - K color for 64 benchmark late-M and L dwarfs, all of which are wide companions to higher-mass stars, and six of which are new discoveries. We assess the correlation between the Δ(J - K) color anomaly (the difference in an object's J - K color from the median color for field objects of the same spectral type) and the metallicity of the host star to investigate how metallicity affects ultracool photospheres. Using Spearman's rank correlation test and Student's t-test, the late-M dwarf (L dwarf) sample's Δ(J - K) and metallicity show a positive correlation at the 95% (90%) confidence level. A linear fit to color anomaly as a function of metallicity finds a slope of 0.17 ± 0.07 for the late-M dwarfs and a slope of ${0.20}_{-0.08}^{+0.07}$ for the L dwarfs. We also computed the Δ(J - K) versus metallicity relationship predicted by multi-metallicity model spectra generated using Drift-Phoenix. The modeled late-M dwarfs show a slope of 0.202 ± 0.03, which is close to our observational results, but the modeled L dwarfs show a slope of 0.493 ± 0.02, steeper than our observational results. Both our empirical results and the models indicate that more metal-rich objects should appear redder photometrically. We speculate that higher metallicity drives more condensate formation in these atmospheres, thus making these ultracool dwarfs appear redder.

Keywords: brown dwarfs; l dwarfs; metallicity; photometry
Dispersion Measures of Fast Radio Burst Host Galaxies Derived from IllustrisTNG Simulation

We calculate the dispersion measures (DMs) contributed by host galaxies of fast radio bursts (FRBs). Based on a few host galaxy observations, a large sample of galaxies with similar properties to observed ones has been selected from the IllustrisTNG simulation. They are used to compute the distributions of host galaxy DMs for repeating and nonrepeating FRBs. For repeating FRBs, we infer the DMhost for FRBs like FRB 121102 and FRB 180916 by assuming that the burst sites are tracing the star formation rates in host galaxies. The median DMshost are 35 (1 + z)1.08 and 96(1 + z)0.83 pc cm-3 for FRBs like FRB 121102 and FRB 180916, respectively. In another case, the median of DMhost is about 30-70 pc cm-3 for nonrepeating FRBs in the redshift range z = 0.1-1.5, assuming that the burst sites are the locations of binary neutron star mergers. In this case, the evolution of the median DMhost can be calculated by 33(1 + z)0.84 pc cm-3. The distributions of DMhost of repeating and nonrepeating FRBs can be well fitted with the log-normal function. Our results can be used to infer redshifts of nonlocalized FRBs.

Keywords: radio transient sources; galaxies; radio bursts
Accelerating Spherical Harmonic Transforms for a Large Number of Sky Maps

The spherical harmonic transform is a powerful tool in the analysis of spherical data sets, such as cosmic microwave background data. In this work, we present a new scheme for spherical harmonic transforms that supports both CPU and GPU computations, which is especially efficient on a large number of sky maps. By comparing our implementation with the standard Libsharp-HEALPix program, we demonstrate a 2-10 times speedup for the CPU implementation, and an up to 30 times speedup when a state-of-the-art GPU is employed. This new scheme's software package is available via an open-source GitHub repository.

Keywords: cosmic microwave background radiation; astronomy data analysis; gpu computing
Collisional Growth within the Solar System's Primordial Planetesimal Disk and the Timing of the Giant Planet Instability

The large-scale structure of the solar system has been shaped by a transient dynamical instability that may have been triggered by the interaction of the giants planets with a massive primordial disk of icy debris. In this work, we investigate the conditions under which this primordial disk could have coalesced into planets using analytic and numerical calculations. In particular, we perform numerical simulations of the solar system's early dynamical evolution that account for the viscous stirring and collisional damping within the disk. We demonstrate that if collisional damping would have been sufficient to maintain a temperate velocity dispersion, Earth-mass trans-Neptunian planets could have emerged within a timescale of 10 Myr. Therefore, our results favor a scenario wherein the dynamical instability of the outer solar system began immediately upon the dissipation of the gaseous nebula to avoid the overproduction of Earth-mass planets in the outer solar system.

Keywords: solar system formation; astrodynamics; trans-neptunian objects
Optical Identification of the Shortest-period Spider Pulsar System M71E

M71E is a spider pulsar (i.e., a millisecond pulsar with a tight binary companion) with the shortest known orbital period of P = 53.3 minutes, which was discovered by Pan et al. Their favored evolutionary model suggests that it bridges between two types of spider pulsars, namely, it descended from a "redback" and will become a "black widow." Using Hubble Space Telescope (HST) archival imaging data, we report the first optical identification of its companion COM-M71E. The HST and pulsar timing coordinates are in excellent agreement (within ~10 mas). If M71E is associated with the globular cluster M71, our measured brightness of COM-M71E (m F606W ≈ 25.3) is broadly consistent with the expectation from Pan et al.'s preferred binary evolutionary model of a stripped dwarf companion, while it is also compatible with an ultralow-mass degenerate companion. Future multiwavelength photometric and spectroscopic observations can characterize the companion and test the evolutionary scenarios.

Keywords: millisecond pulsars; binary pulsars; optical identification; globular star clusters
Manganese Indicates a Transition from Sub- to Near-Chandrasekhar Type Ia Supernovae in Dwarf Galaxies

Manganese abundances are sensitive probes of the progenitors of Type Ia supernovae (SNe Ia). In this work, we present a catalog of manganese abundances in dwarf spheroidal satellites of the Milky Way, measured using medium-resolution spectroscopy. Using a simple chemical evolution model, we infer the manganese yield of SNe Ia in the Sculptor dwarf spheroidal galaxy (dSph) and compare to theoretical yields. The sub-solar yield from SNe Ia ([Mn/Fe]_{Ia}=-{0.30}_{-0.03}^{+0.03} at [Fe/ H] = -1.5 dex, with negligible dependence on metallicity) implies that sub-Chandrasekhar-mass (sub-MCh) white dwarf progenitors are the dominant channel of SNe Ia at early times in this galaxy, although some fraction (≳20%) of MCh Type Ia or Type Iax SNe are still needed to produce the observed yield. First-order corrections for deviations from local thermodynamic equilibrium increase the inferred [Mn/Fe]_{Ia} by as much as ∼0.3 dex. However, our results also suggest that the nucleosynthetic source of SNe Ia may depend on environment. In particular, we find that dSphs with extended star formation histories (Leo I, Fornax dSphs) appear to have higher [Mn/Fe] at a given metallicity than galaxies with early bursts of star formation (Sculptor dSph), suggesting that MCh progenitors may become the dominant channel of SNe Ia at later times in a galaxy's chemical evolution.

Keywords: dwarf spheroidal galaxies; dwarf galaxies; sculptor dwarf elliptical galaxy; type ia supernovae; chemical abundances; galaxy abundances; stellar abundances
Survey of CH3NH2 and its Formation Process

We present the observational results of a precursor of glycine, methylamine (CH3NH2), together with methanol (CH3OH) and methanimine (CH2NH) for the high-mass star-forming regions NGC 6334I, G10.47+0.03, G31.41+0.3, and W51 e1/e2 using the Atacama Large Millimeter/submillimeter Array. The molecular abundances of these sources were derived using the CASSIS spectrum analyzer and compared with our state-of-the-art three-phase chemical model NAUTILUS. We found that the observed abundance ratio of CH3NH2/CH3OH is between 0.008 and 1.0 for all sources, except for NGC 6334I MM3, where a ratio less than 0.002 is found. This may be due to its later evolutionary stage relative to the other cores. We also found that the observed CH3NH2/CH3OH ratio agrees well with the three-phase chemical model NAUTILUS, which includes the formation of CH3NH2 on the grain surface via a series of hydrogenation processes of HCN. This result clearly shows the importance of hydrogenation processes to form CH3NH2.

Keywords: astrobiology; interstellar medium; interstellar molecules; interstellar abundances; star formation
The Effects of Metallicity and Abundance Pattern of the ISM on Supernova Feedback

Supernova (SN) feedback plays a vital role in the evolution of galaxies. While modern cosmological simulations capture the leading structures within galaxies, they struggle to provide sufficient resolution to study small-scale stellar feedback, such as the detailed evolution of SN remnants. It is thus common practice to assume subgrid models that are rarely extended to low metallicities and that routinely use the standard solar abundance pattern. With the aid of 1D hydrodynamical simulations, we extend these models to consider low metallicities and nonsolar abundance patterns as derived from spectra of Milky Way stars. For that purpose, a simple, yet effective framework has been developed to generate nonsolar abundance pattern cooling functions. We find that previous treatments markedly over-predict SN feedback at low metallicities and show that non-negligible changes in the evolution of SN remnants of up to ≈50% in cooling mass and ≈27% in momentum injection from SN remnants arise from nonsolar abundance patterns. We use our simulations to quantify these results as a function of metallicity and abundance pattern variations and present analytic formulas to accurately describe the trends. These formulas have been designed to serve as subgrid models for SN feedback in cosmological hydrodynamical simulations.

Keywords: interstellar medium; supernova remnants; astronomical simulations; galaxy evolution
MeerKAT 1.3 GHz Observations of Supernova Remnants

We present full Stokes MeerKAT L-band (856-1712 MHz) observations of 36 high-latitude supernova remnants (SNRs). Sensitive, high-dynamic-range images show a wealth of structure. G15.1-1.6 appears to be a H II region rather than an SNR. G30.7-2.0 consists of three background extragalactic sources which appear to form an arc when imaged with much lower resolution. At least half of the remnants in the sample contain "blowouts" or "ears," showing these to be a common feature. Analysis of the polarimetric data reveals details of the magnetic field structure in the emitting regions of the remnants as well as magnetized thermal plasma in front of polarized emission. The chance alignment of G327.6+14.6 with a background active galactic nucleus with very extended polarized jets allows testing for the presence of Faraday effects in the interior of the remnant. Scant evidence of Faraday rotating material is found in the interior of this remnant.

Keywords: supernova remnants