adsabs/SciX_UAT_keywords huggingface dataset:
Effects of an Immortal Stellar Population in AGN Disks

Stars are likely embedded in the gas disks of active galactic nuclei (AGN). Theoretical models predict that in the inner regions of the disk, these stars accrete rapidly, with fresh gas replenishing hydrogen in their cores faster than it is burned into helium, effectively stalling their evolution at hydrogen burning. We produce order-of-magnitude estimates of the number of such stars in a fiducial AGN disk. We find numbers of order 102-4, confined to the inner r cap ~ 3000r s ~ 0.03 pc. These stars can profoundly alter the chemistry of AGN disks, enriching them in helium and depleting them in hydrogen, both by order-unity amounts. We further consider mergers between these stars and other disk objects, suggesting that star-star mergers result in rapid mass loss from the remnant to restore an equilibrium mass, while star-compact object mergers may result in exotic outcomes and even host binary black hole mergers within themselves. Finally, we examine how these stars react as the disk dissipates toward the end of its life, and find that they may return mass to the disk fast enough to extend its lifetime by a factor of several and/or may drive powerful outflows from the disk. Post-AGN, these stars rapidly lose mass and form a population of stellar mass black holes around 10M ⊙. Due to the complex and uncertain interactions between embedded stars and the disk, their plausible ubiquity, and their order-unity impact on disk structure and evolution, they must be included in realistic disk models.

Keywords: stellar physics; stellar evolutionary models; massive stars; quasars
PHANGS Hubble Space Telescope Treasury Survey: Globular Cluster Systems in 17 Nearby Spiral Galaxies

We present new catalogs of likely globular clusters (GCs) in 17 nearby spiral galaxies studied as part of the PHANGS Hubble Space Telescope (HST) Treasury Survey. The galaxies were imaged in five broadband filters from the near-ultraviolet through the I band. PHANGS-HST has produced catalogs of stellar clusters of all ages by selecting extended sources (from multiple concentration index measurements) followed by morphological classification (centrally concentrated and symmetric or asymmetric, multiple peaks, and contaminants) by visually examining the V-band images and separately by a machine-learning algorithm which classified larger samples to reach fainter limits. From both cluster catalogs, we select an initial list of candidate GCs which have B ‑ V ≥ 0.5 and V ‑ I ≥ 0.73 mag, then remove likely contaminants (including reddened young clusters, background galaxies misclassified by the neural network, and chance superpositions/blends of stars) after a careful visual inspection. We find that ≈86% of the color-selected candidates classified as spherically symmetric and 68% of those classified as centrally concentrated but asymmetric are likely to be GCs. The luminosity functions of the GC candidates in two of our 17 galaxies, NGC 628 and NGC 3627, are atypical, and continue to rise at least 1 mag fainter than the expected turnover near M V ∼ ‑7.4. These faint candidate GCs have more extended spatial distributions than their bright counterparts, and may reside in the disk rather than the bulge/halo, similar to faint GCs previously discovered in M101. These faint clusters may be somewhat younger since the age–metallicity degeneracy makes it difficult to determine precise cluster ages from integrated colors once they reach ≈1 Gyr.

Keywords: globular star clusters; spiral galaxies
A Strongly Lensed Dusty Starburst of an Intrinsic Disk Morphology at a Photometric Redshift of z ph > 7

We present COSBO-7, a strong millimeter source known for more than 16 yr that just revealed its near-to-mid-IR counterpart with the James Webb Space Telescope (JWST). The precise pinpointing by the Atacama Large Millimeter/submillimeter Array on the exquisite NIRCam and MIRI images show that it is a background source gravitationally lensed by a single foreground galaxy, and the analysis of its spectral energy distribution by different tools is in favor of photometric redshift at z ph > 7. Strikingly, our lens modeling based on the JWST data shows that it has a regular disk morphology in the source plane. The dusty region giving rise to the far-IR-to-millimeter emission seems to be confined to a limited region to one side of the disk and has a high dust temperature of >90 K. The galaxy is experiencing starburst both within and outside of this dusty region. After taking the lensing magnification of μ ≈ 2.5–3.6 into account, the intrinsic star formation rate is several hundred M ⊙ yr‑1 both within the dusty region and across the more extended stellar disk, and the latter already has >1010 M ⊙ of stars in place. If it is indeed at z > 7, COSBO-7 presents an extraordinary case that is against the common wisdom about galaxy formation in the early Universe; simply put, its existence poses a critical question to be answered: how could a massive disk galaxy come into being so early in the Universe and sustain its regular morphology in the middle of an enormous starburst?

Keywords: high-redshift galaxies; starburst galaxies; infrared galaxies; gravitational lensing; galaxy disks
A Probabilistic Autoencoder for Type Ia Supernova Spectral Time Series

We construct a physically parameterized probabilistic autoencoder (PAE) to learn the intrinsic diversity of Type Ia supernovae (SNe Ia) from a sparse set of spectral time series. The PAE is a two-stage generative model, composed of an autoencoder that is interpreted probabilistically after training using a normalizing flow. We demonstrate that the PAE learns a low-dimensional latent space that captures the nonlinear range of features that exists within the population and can accurately model the spectral evolution of SNe Ia across the full range of wavelength and observation times directly from the data. By introducing a correlation penalty term and multistage training setup alongside our physically parameterized network, we show that intrinsic and extrinsic modes of variability can be separated during training, removing the need for the additional models to perform magnitude standardization. We then use our PAE in a number of downstream tasks on SNe Ia for increasingly precise cosmological analyses, including the automatic detection of SN outliers, the generation of samples consistent with the data distribution, and solving the inverse problem in the presence of noisy and incomplete data to constrain cosmological distance measurements. We find that the optimal number of intrinsic model parameters appears to be three, in line with previous studies, and show that we can standardize our test sample of SNe Ia with an rms of 0.091 ± 0.010 mag, which corresponds to 0.074 ± 0.010 mag if peculiar velocity contributions are removed. Trained models and codes are released at https://github.com/georgestein/suPAErnova.

Keywords: type ia supernovae; standard candles; observational cosmology
Mirror-wave Structures in the Solar Wind: Grad-Shafranov Reconstruction, MHD, and Hall MHD Simulations with Double-polytropic Energy Closures

Mirror-mode waves with anticorrelated density and magnetic field are widely observed in the solar wind and planetary magnetospheres. In this study we analyze the characteristics of three mirror-wave events observed by the Magnetospheric Multiscale Mission in the Earth's magnetosheath based on the Grad-Shafranov (GS) reconstruction model with temperature anisotropy. The GS scheme solves steady, two-dimensional MHD equations with field-aligned flow from the plasma and magnetic field measurements taken by a single spacecraft traversing across a coherent field structure. The reconstructed 2D plasma and field maps are obtained in the de Hoffmann-Teller frame and on the plane perpendicular to the invariant axis. The energy closures are a set of empirical energy laws with two polytropic exponents inferred from the observed mirror events which are in the ranges of ${\gamma }_{\perp }=0.6\sim 0.89$ and ${\gamma }_{| | }=0.99\sim 1.35$ . It is shown that the mirror waves are nonpropagating with linear magnetic field polarization and possess anticorrelated density, temperatures, and magnetic field with the widths of 10-40 ion inertial lengths. The double-polytropic MHD and Hall MHD simulations of mirror instability show consistent results with the GS reconstructions in terms of field-line geometry, phase relations and the sizes of mirror waves, etc.

Keywords: magnetohydrodynamics; magnetohydrodynamical simulations; alfven waves; space plasmas; solar wind; plasma physics
Investigation of Nonequilibrium Ionization Plasma during a Giant Flare of UX Arietis Triggered with MAXI and Observed with NICER

We detected a giant X-ray flare from the RS CVn–type binary star UX Ari using the Monitor of All-sky X-ray Image on 2020 August 17 and started a series of Neutron star Interior Composition Explorer observations 89 minutes later. For a week, the entire duration of the flare was covered with 32 snapshot observations including the rising phase. The X-ray luminosity reached 2 × 1033 erg s‑1, and the entire energy release was ∼1038 erg in the 0.5–8.0 keV band. X-ray spectra characterized by continuum emission with lines of Fe XXV Heα and Fe XXVI Lyα were obtained. We found that the temperature peaks before the flux does, which suggests that the period of plasma formation in the magnetic flare loop was captured. Using the continuum information (temperature, flux, and their delay time), we estimated the flare loop size to be ∼3 × 1011 cm and the peak electron density to be ∼4 × 1010 cm‑3. Furthermore, using the line ratio of Fe XXV and Fe XXVI, we investigated any potential indications of deviation from collisional ionization equilibrium (CIE). The X-ray spectra were consistent with CIE plasma throughout the flare, but the possibility of an ionizing plasma away from CIE was not rejected in the flux rising phase.

Keywords: plasma astrophysics; space plasmas
VLT/CRIRES Science Verification Observations: A hint of C18O in the Young Brown Dwarf 2M0355

Chemical and isotopic composition provide insights into the formation and evolution history of planets and brown dwarfs. Recent measurements of 12CO/13CO abundance ratios in the atmosphere of the young super-Jupiter YSES-1b and the isolated brown dwarf 2MASS J03552337+1133437 may point to distinct formation pathways. Here we present our analysis of 0.5 hr of science verification observations using the recently upgraded CRIRES spectrograph at ESO's Very Large Telescope on the same brown dwarf, with the aim to detect C18O and determine the 16O/18O isotope ratio. Our free retrieval analyses confirm the previous measurement of the carbon isotope ratio, and the inclusion of the C18O molecule in our models enables an initial tentative constraint of 16O/18O = ${1489}_{-426}^{+1027}$ on the oxygen isotope ratio, but this requires more data to be confirmed. These short observations showcase the prospect of studying the isotope inventory in brown dwarfs and super-Jovian exoplanets with high-dispersion spectroscopy.

Keywords: brown dwarfs; exoplanet atmospheres
Sandblasting the r-process: Spallation of Ejecta from Neutron Star Mergers

Neutron star mergers (NSMs) are rapid neutron-capture (r-process) nucleosynthesis sites that expel matter at high velocities, from 0.1c to as high as 0.6c. Nuclei ejected at these speeds are sufficiently energetic to initiate spallation nuclear reactions with interstellar medium (ISM) particles. We adopt a thick-target model for the propagation of high-speed heavy nuclei in the ISM, similar to the transport of cosmic rays. We find that spallation may create observable perturbations to NSM isotopic abundances, particularly around the low-mass edges of the r-process peaks where neighboring nuclei have very different abundances. The extent to which spallation modifies the final NSM isotopic yields depends on: (1) the ejected abundances, which are determined by the NSM astrophysical conditions and the properties of nuclei far from stability, (2) the ejecta velocity distribution and propagation in interstellar matter, and (3) the spallation cross sections. Observed solar and stellar r-process yields could thus constrain the velocity distribution of ejected neutron star matter, assuming NSMs are the dominant r-process source. We suggest avenues for future work, including measurement of relevant cross sections.

Keywords: cosmic rays; r-process; nucleosynthesis; nuclear reaction cross sections; nuclear abundances; compact binary stars
Unveiling a Hidden Bar-like Structure in NGC 1087: Kinematic and Photometric Evidence Using MUSE/VLT, ALMA, and JWST

We report a faint nonaxisymmetric structure in NGC 1087 through the use of James Webb Space Telescope Near Infrared Camera, with an associated kinematic counterpart observed as an oval distortion in the stellar velocity map, Hα, and CO J = 2 → 1 velocity fields. This structure is not evident in the MUSE optical continuum images but only revealed in the near-IR with the F200W and F300M band filters at 2 μm and 3 μm, respectively. Due to its elongation, this structure resembles a stellar bar although with remarkable differences with respect to conventional stellar bars. Most of the near-IR emission is concentrated within 6″∼500 pc with a maximum extension up to 1.2 kpc. The spatial extension of the large-scale noncircular motions is coincident with the bar, which undoubtedly confirms the presence of a nonaxisymmetric perturbation in the potential of NGC 1087. The oval distortion is enhanced in CO due to its dynamically cold nature rather than in Hα. We found that the kinematics in all phases, including stellar, ionized, and molecular, can be described simultaneously by a model containing a bisymmetric perturbation; however, we find that an inflow model of gas along the bar major axis is also likely. Furthermore, the molecular mass inflow rate associated can explain the observed star-formation rate in the bar. This reinforces the idea that bars are mechanisms for transporting gas and triggering star formation. This work contributes to our understanding of nonaxisymmetry in galaxies using the most sophisticated data so far.

Keywords: barred spiral galaxies; stellar kinematics
Tides in the High-eccentricity Migration of Hot Jupiters: Triggering Diffusive Growth by Nonlinear Mode Interactions

High-eccentricity migration is a possible formation channel for hot Jupiters. However, in order for it to be consistent with the observed population of planets, tides must circularize the orbits in an efficient manner. A potential mechanism for such rapid circularization is the diffusive growth of the tidally driven planetary f-mode. Such growth occurs if the f-mode phase at pericenter varies chaotically from one pericenter passage to the next. Previous studies focused on the variation of the orbital period due to tidal back-reaction on the orbit as the source of chaos. Here we show that nonlinear mode interactions can also be an important source. Specifically, we show that nonlinear interactions between a parent f-mode and daughter f-/p-modes induce an energy-dependent shift in the oscillation frequency of the parent. This frequency shift varies randomly from orbit to orbit because the parents' energy varies. As a result, the parents' phase at pericenter varies randomly, which we find can trigger it to grow diffusively. We show that the phase shift induced by nonlinear mode interactions in fact dominates the shift induced by tidal back-reaction and lowers the one-kick energy threshold for diffusive growth by about a factor of 5 compared to the prediction from the linear theory. For a given pericenter distance, this reduces the semimajor axis needed to trigger diffusive growth from ≳2 au to ≃1 au. Nonlinear interactions could thus enhance the formation rate of hot Jupiters through the high-eccentricity migration channel and potentially mitigate the discrepancy between the observed and predicted occurrence rates for close-in gas giants as compared to those farther from the star.

Keywords: exoplanets; hot jupiters; exoplanet tides; exoplanet migration; hydrodynamics
Quantifying the Magnetic Structure of a Coronal Shock Producing a Type II Radio Burst

Type II radio bursts are thought to be produced by shock waves in the solar atmosphere. However, what magnetic conditions are needed for the generation of type II radio bursts is still a puzzling issue. Here, we quantify the magnetic structure of a coronal shock associated with a type II radio burst. Based on multiperspective extreme-ultraviolet observations, we reconstruct the three-dimensional (3D) shock surface. By using a magnetic field extrapolation model, we then derive the orientation of the magnetic field relative to the normal of the shock front (θ Bn) and the Alfvén Mach number (M A ) on the shock front. Combining the radio observations from the Nancay Radio Heliograph, we obtain the source region of the type II radio burst on the shock front. It is found that the radio burst is generated by a shock with M A ≳ 1.5 and a bimodal distribution of θ Bn. We also use the Rankine-Hugoniot relations to quantify the properties of the shock downstream. Our results provide a quantitative 3D magnetic structure condition of a coronal shock that produces a type II radio burst.

Keywords: solar coronal mass ejection shocks; shocks
Probing Polarization and the Role of Magnetic Fields in Cloud Destruction in the Keyhole Nebula

We present polarimetric observations of the Keyhole Nebula in the Carina Nebula Complex carried out using the Stratospheric Observatory for Infrared Astronomy. The Keyhole Nebula, located to the west of η Carinae, is believed to be disturbed by the stellar winds from the massive star. We observed the Keyhole Nebula at 89 μm wavelength with the HAWC+ instrument. The observations cover the entire Keyhole Nebula spanning 8' by 5' with central position R.A. = 10:44:43 and decl. = -59:38:04. The typical uncertainty of polarization measurement is less than 0.5% in the region with intensity above 5500 MJy sr-1. The polarization fraction has a mean value of 2.4% with a standard deviation of 1.6% in the region above this intensity, similar to values in other high-mass star-forming regions. The magnetic field orientation in the bar-shaped structure is similar to the large-scale magnetic field orientation. On the other hand, the magnetic field direction in the loop is not aligned with the large-scale magnetic fields but is tightly aligned with the loop itself. Analysis of the magnetic field angles and the gas turbulence suggests that the field strength is ~70 μG in the loop. A simple comparison of the magnetic field tension to the ram pressure of η Carinae's stellar wind suggests that the magnetic fields in the Keyhole Nebula are not strong enough to maintain the current structure against the impact of the stellar wind and that the role of the magnetic field in resisting stellar feedback in this region is limited.

Keywords: molecular clouds; photodissociation regions; polarimetry; far infrared astronomy
An Insight-HXMT View of the mHz Quasi-regular Modulation Phenomenon in the Black Hole X-Ray Binary 4U 1630-47

Here we report the spectral-timing results of the black hole X-ray binary 4U 1630-47 during its 2021 outburst using observations from the Hard X-ray Modulation Telescope (Insight-HXMT). Type C quasi-periodic oscillations (QPOs) in ~1.6-4.2 Hz and quasi-regular modulation (QRM) near 60 mHz are detected during the outburst. The mHz QRM has a fractional rms of ~10%-16% in the 8-35 keV energy band with a Q factor (frequency/width) of ~2-4. Benefiting from the broad energy band of Insight-HXMT, we study the energy dependence of the ~60 mHz QRM in 1-100 keV for the first time. We find that the fractional rms of the mHz QRM increases with photon energy, while the time lags of the mHz QRM are soft and decrease with photon energy. Fast recurrence of the mHz QRM, in a timescale of less than 1 hr, has been observed during the outburst. During this period, the corresponding energy spectra moderately change when the source transitions from the QRM state to the non-QRM state. The QRM phenomenon also shows a dependence with the accretion rate. We suggest that the QRM could be caused by an unknown accretion instability aroused from the corona.

Keywords: accretion; astrophysical black holes; low-mass x-ray binary stars; stellar mass black holes
A Submillimeter Perspective on the GOODS Fields (SUPER GOODS). V. Deep 450 μm Imaging

We present deep SCUBA-2 450 μm imaging of the two GOODS fields, achieving a central rms of 1.14 mJy for the GOODS-N and 1.86 mJy for the GOODS-S. For each field, we give a catalog of >4σ detections (79 and 16 sources, respectively). We construct the 450 μm number counts, finding excellent agreement with others from the literature. We match the 450 μm sources to 20 cm data (both fields) and ALMA 870 μm data (GOODS-S) to gauge the accuracy of the 450 μm positions. We use the extensive redshift information available on the fields to test how well redshift can be estimated from simple flux ratios (450 μm /850 μm and 20 cm/850 μm), finding tight correlations. We provide a catalog of candidate high-redshift submillimeter galaxies. We look for evolution in dust temperature with redshift by fitting the spectral energy distributions of the sources, but we do not find any significant redshift evolution after accounting for the far-infrared luminosity. We do not find evidence for the 450 μm selection picking out warmer sources than an 850 μm selection. We find that a 450 μm-selected sample only adds low-redshift (z < 1.5) galaxies beyond an 850 μm sample.

Keywords: galaxy evolution
Reconstructing Masses of Merging Neutron Stars from Stellar r-process Abundance Signatures

Neutron star mergers (NSMs) are promising astrophysical sites for the rapid neutron-capture ("r") process, but can their integrated yields explain the majority of heavy-element material in the Galaxy? One method to address this question implements a forward approach that propagates NSM rates and yields along with stellar formation rates and compares those results with observed chemical abundances of r-process-rich, metal-poor stars. In this work, we take the inverse approach by utilizing r-process-element abundance ratios of metal-poor stars as input to reconstruct the properties—especially the masses—of their neutron star (NS) binary progenitors. This novel analysis provides an independent avenue for studying the population of the original NS binary systems that merged and produced the r-process material now incorporated in Galactic metal-poor halo stars. We use ratios of elements typically associated with the limited-r-process and the actinide region to those in the lanthanide region (i.e., Zr/Dy and Th/Dy) to probe the NS masses of the progenitor merger. We find that NSMs can account for all r-process material in metal-poor stars that display r-process signatures, while simultaneously reproducing the present-day distribution of double-NS systems. Notably, with our model assumptions and the studied stellar sample, we postulate that the most r-process enhanced stars (the r-II stars) on their own would require progenitor NSMs of asymmetric systems that are distinctly different from present ones in the Galaxy. We also explore variations to the model and find that the predicted degree of asymmetry is most sensitive to the electron fraction of the remnant disk wind.

Keywords: nuclear astrophysics; nucleosynthesis; r-process; neutron stars; chemically peculiar stars; population ii stars; compact binary stars