Sazuna/UAT_keywords huggingface dataset:
Synthetic Observations of the Infalling Rotating Envelope: Links between the Physical Structure and Observational Features. We performed synthetic observations of the Ulrich, Cassen, and Moosman (UCM) model to understand the relation between the physical structures of the infalling envelope around a protostar and their observational features in molecular lines, adopting L1527 as an example. We also compared the physical structure and synthetic position-velocity (P-V) diagrams of the UCM model and a simple ballistic (SB) model. There are multiple ways to compare synthetic data with observational data. We first calculated the correlation coefficient. The UCM model and the SB model show similarly good correlation with the observational data. While the correlation reflects the overall similarity between the cube datasets, we can alternatively compare specific local features, such as the centrifugal barrier in the SB model or the centrifugal radius in the UCM model. We evaluated systematic uncertainties in these methods. In the case of L1527, the stellar mass values estimated using these methods are all lower than the value derived from previous Keplerian analysis of the disk. This may indicate that the gas infall motion in the envelope is retarded by, e.g., magnetic fields. We also showed analytically that, in the UCM model, the spin-up feature of the P-V diagram is due to the infall velocity rather than the rotation. The line-of-sight velocity V is thus ∝x -0.5, where x is the offset. If the infall is retarded, rotational velocity should dominate so that V is proportional to x -1, as is often observed in the protostellar envelope.

Keywords: Protostars, Star formation, Astrochemistry
Exploring the Circumstellar Environment of Tycho's Supernova Remnant. I. The Hydrodynamic Evolution of the Shock. Among Type Ia supernova remnants (SNRs), Tycho's SNR has been considered as a typical object from the viewpoints of its spectroscopic, morphological, and environmental properties. A recent reanalysis of Chandra data showed that its forward shock is experiencing a substantial deceleration since around 2007, which suggests recent shock interactions with a dense medium as a consequence of a cavity-wall environment inside a molecular cloud. Such a nonuniform environment can be linked back to the nature and activities of its progenitor. In this study, we perform hydrodynamic simulations to characterize Tycho's cavity-wall environment using the latest multiepoch proper motion measurements of the forward shock. A range of parameters for the environment is explored in the hydrodynamic models to fit with the observational data for each azimuthal region. Our results show that a wind-like cavity with ρ(r) ∝ r -2 reconciles with the latest data better than a uniform medium with a constant density. In addition, our best-fit model favors an anisotropic wind with an azimuthally varying wind parameter. The overall result indicates a mass-loss rate which is unusually high for the conventional single-degenerate explosion scenario.

Keywords: Molecular clouds, Supernova remnants, Circumstellar matter, Type Ia supernovae, Proper motions, X-ray sources
A Pathway for Collisional Planetesimal Growth in the Ice-dominant Regions of Protoplanetary Disks. We present a semi-analytic model for the growth, drift, desorption, and fragmentation of millimeter- to meter-sized particles in protoplanetary disks. Fragmentation occurs where particle collision velocities exceed critical fragmentation velocities. Using this criterion, we produce fragmentation regions in disk orbital radius-particle size phase space for particles with a range of material properties, structures, and compositions (including SiO2, Mg2SiO4, H2O, CO2, and CO). For reasonable disk conditions, compact aggregate H2O, CO2, and CO ice particles do not reach destructive relative velocities and are thus not likely to undergo collisional fragmentation. Uncoated silicate particles are more susceptible to collisional destruction and are expected to fragment in the inner disk, consistent with previous work. We then calculate the growth, drift, and sublimation of small particles, initially located in the outer disk. We find that ice-coated particles can avoid fragmentation as they grow and drift inward under a substantial range of disk conditions, as long as the particles are aggregates composed of 0.1 μm-sized monomers. Such particles may undergo runaway growth in disk regions abundant in H2O or CO2 ice, depending on the assumed disk temperature structure. These results indicate that icy collisional growth to planetesimally relevant sizes may happen efficiently throughout a disk's lifetime, and is particularly robust at early times when the disk's dust-to-gas ratio is comparable to that of the interstellar medium.

Keywords: Ice composition, Ice physics, Collision physics, Surface ices, Protoplanetary disks, Planetesimals, Planet formation
Signatures of Massive Black Hole Merger Host Galaxies from Cosmological Simulations. I. Unique Galaxy Morphologies in Imaging. Low-frequency gravitational-wave experiments such as the Laser Interferometer Space Antenna and pulsar timing arrays are expected to detect individual massive black hole (MBH) binaries and mergers. However, secure methods of identifying the exact host galaxy of each MBH merger among the large number of galaxies in the gravitational-wave localization region are currently lacking. We investigate the distinct morphological signatures of MBH merger host galaxies, using the Romulus25 cosmological simulation. We produce mock telescope images of 201 simulated galaxies in Romulus25 hosting recent MBH mergers through stellar population synthesis and dust radiative transfer. Based on comparisons to mass- and redshift-matched control samples, we show that combining multiple morphological statistics via a linear discriminant analysis enables identification of the host galaxies of MBH mergers, with accuracies that increase with chirp mass and mass ratio. For mergers with high chirp masses (≳108.2 M ☉) and high mass ratios (≳0.5), the accuracy of this approach reaches ≳80%, and does not decline for at least ~1 Gyr after numerical merger. We argue that these trends arise because the most distinctive morphological characteristics of MBH merger and binary host galaxies are prominent classical bulges, rather than relatively short-lived morphological disturbances from their preceding galaxy mergers. Since these bulges are formed though major mergers of massive galaxies, they lead to (and become permanent signposts for) MBH binaries and mergers that have high chirp masses and mass ratios. Our results suggest that galaxy morphology can aid in identifying the host galaxies of future MBH binaries and mergers.

Keywords: Supermassive black holes, Gravitational wave sources, Radiative transfer simulations, N-body simulations, Galaxies
Modeling Noncondensing Compositional Convection for Applications to Super-Earth and Sub-Neptune Atmospheres. Compositional convection is atmospheric mixing driven by density variations caused by compositional gradients. Previous studies have suggested that compositional gradients of atmospheric trace species within planetary atmospheres can impact convection and the final atmospheric temperature profile. In this work, we employ 3D convection-resolving simulations using Cloud Model 1 (CM1) to gain a fundamental understanding of how compositional variation influences convection and the final atmospheric state of exoplanet atmospheres. We perform 3D initial value problem simulations of noncondensing compositional convection for Earth-air, H2, and CO2 atmospheres. Conventionally, atmospheric convection is assumed to mix the atmosphere to a final, marginally stable state defined by a unique temperature profile. However, when there is compositional variation within an atmosphere, a continuous family of stable end states is possible, differing in the final state composition profile. Our CM1 simulations are used to determine which of the family of possible compositional end states is selected. Leveraging the results from our CM1 simulations, we develop a dry convective adjustment scheme for use in general circulation models (GCMs). This scheme relies on an energy analysis to determine the final adjusted atmospheric state. Our convection scheme produces results that agree with our CM1 simulations and can easily be implemented in GCMs to improve modeling of compositional convection in exoplanet atmospheres.

Keywords: Exoplanets, Super Earths, Planetary atmospheres, Planetary climates, Mini Neptunes, Exoplanet atmospheres, Atmospheric science
A Markedly Expanded Sample of Candidate X-Ray-emitting Isolated Neutron Stars. The current sample of 12 radio-quiet isolated neutron stars that emit strongly in X-rays (XINSs) is both small and heterogeneous, limiting its usefulness for understanding the physics of neutron star atmospheres and cooling rates and for constraining the equation of state of neutron degenerate matter. Utilizing the ROSAT 1RXS and 2RXS data sets, in conjunction with the Sloan Digital Sky Survey Data Release 17 and other companion multiwavelength surveys, we have extended previous searches for blank-field X-ray source candidate XINSs, ultimately recovering two known XINSs while identifying 46 new, unstudied candidate fields devoid of likely multiwavelength counterparts. In this publication, we describe our selection approach and provide detailed information regarding our sample of new candidate XINSs. Future opportunities to verify or to refute these X-ray sources as isolated neutron stars by obtaining more accurate X-ray source positions, quality X-ray spectra, or deeper optical imaging are also discussed.

Keywords: Neutron stars, X-ray surveys
Disappearing Galaxies: The Orientation Dependence of JWST-bright, HST-dark, Star-forming Galaxy Selection. Galaxies that are invisible in deep optical-near-infrared imaging but detected at longer wavelengths have been the focus of several recent observational studies, with speculation that they could constitute a substantial missing population and even dominate the cosmic star formation rate density at z ≳ 4. The depths now achievable with JWST at the longest wavelengths probed by the Hubble Space Telescope (HST), coupled with the transformative resolution at longer wavelengths, are already enabling detailed, spatially resolved characterization of sources that were invisible to HST, often known as "HST-dark" galaxies. However, until now, there has been little theoretical work to compare against. We present the first simulation-based study of this population, using highly resolved galaxies from the Feedback in Realistic Environments project, with multiwavelength images along several lines of sight forward-modeled using radiative transfer. We naturally recover a population of modeled sources that meet commonly used selection criteria (H AB &gt; 27 mag and H AB - F444W &gt; 2.3). These simulated HST-dark galaxies lie at high redshifts (z = 4-7), have high levels of dust attenuation (A  V  = 2-4), and display compact recent star formation (R 1/2,4.4 μm ≲ 1 kpc). Orientation is very important: for all but one of the 17 simulated galaxy snapshots with HST-dark sight lines, there exist other sight lines that do not meet the criteria. This result has important implications for comparisons between observations and models that do not resolve the detailed star-dust geometry, such as semianalytic models or coarsely resolved hydrodynamical simulations. Critically, we demonstrate that HST-dark sources are not an unexpected or exotic population, but a subset of high-redshift, highly dust-attenuated sources viewed along certain lines of sight.

Keywords: Radiative transfer simulations, High-redshift galaxies, Galaxy evolution
A Possible Optical Quasiperiodic Oscillation of 134 days in the Radio-loud Narrow-line Seyfert 1 Galaxy TXS 1206+549 at z = 1.34. Here we report an optical quasiperiodic oscillation (QPO) with a period of ~134 days detected in g- and r-band light curves of the narrow-line Seyfert 1 galaxy TXS 1206+549 at a redshift of 1.34 with data from observations at the Zwicky Transient Facility (ZTF). After considering the trial factor, the significance levels in the two bands are 3.1σ and 2.6σ, respectively. The QPO signal presents about 10 cycles ranging from 2018 March to 2021 December, thus lasting ~4 yr. A nearly sinusoidal profile also appears in the folded light curves by using a phase-resolved analysis. Interestingly, in the simultaneous light curve with the timescale of ZTF observations, a potential periodic signal with a similar period is detected in the o-band light curve from Asteroid Terrestrial-impact Last Alert System data; additionally, a weak peak is also detected at a similar period in the γ-ray light curve obtained from Fermi Gamma-ray Space Telescope data. Some potential origins of periodicities in active galactic nuclei are discussed for the QPO reported here.

Keywords: Period search , Active galactic nuclei, Time series analysis
Nature versus Nurture: Revisiting the Environmental Impact on Star Formation Activities of Galaxies. We present a systematic study of the environmental impact on star formation activities of galaxies using a mass-complete sample of ~170k galaxies at z &lt; 4 from the latest COSMOS2020 catalog. At z &lt; 1, we find that the mean star formation rate (SFR) of all galaxies decreases with increasing density of the environment. However, when we only consider star-forming galaxies, the mean SFR becomes independent of the environment at z &lt; 1. At z &gt; 2, we observe a clear positive correlation between the SFR and the density of the environment for all the galaxies. On the other hand, the stellar mass of the galaxies increases significantly with the environment at all redshifts except for star-forming galaxies at z &lt; 1. The fraction of quiescent galaxies increases with increasing density of the environment at z &lt; 2, and the morphology-density relation is confirmed to be present up to z ~ 1. We also find that environmental quenching is negligible at z &gt; 1, whereas mass quenching is the dominant quenching mechanism for massive galaxies at all redshifts. Based on these results, we argue that stellar mass-regulated physical processes might be the major driving force for star formation activities of galaxies. At low redshift (z &lt; 1) massive galaxies are quenched primarily due to their high mass, resulting in a normal SFR-density relation. At high redshift (z &gt; 2) most of the galaxies are star-forming ones tightly following the star-forming main sequence, and the difference in their stellar mass in different environments naturally leads to a reversal of the SFR-density relation.

Keywords: Galaxy environments
Differential Rotation of the Solar Chromosphere: A Century-long Perspective from Kodaikanal Solar Observatory Ca II K Data. Chromospheric differential rotation is a key component in comprehending the atmospheric coupling between the chromosphere and the photosphere at different phases of the solar cycle. In this study, we therefore utilize the newly calibrated multidecadal Ca II K spectroheliograms (1907-2007) from the Kodaikanal Solar Observatory (KoSO) to investigate the differential rotation of the solar chromosphere using the technique of image cross-correlation. Our analysis yields the chromospheric differential rotation rate Ω(θ) = (14.61 ± 0.04-2.18 ± 0.37 ${\sin }^{2}\theta -1.10\pm 0.61{\sin }^{4}\theta )^\circ $ day-1. These results suggest the chromospheric plages exhibit an equatorial rotation rate 1.59% faster than the photosphere when compared with the differential rotation rate measured using sunspots and also a smaller latitudinal gradient compared to the same. To compare our results to those from other observatories, we have applied our method on a small sample of Ca II K data from Rome, Meudon, and Mount Wilson observatories, which support our findings from KoSO data. Additionally, we have not found any significant north-south asymmetry or any systematic variation in chromospheric differential rotation over the last century.

Keywords: Solar cycle, Solar rotation, Solar differential rotation, Plages, Solar chromosphere
Comparing Plasma Anisotropy Associated with Solar Wind Discontinuities and Alfvénic Fluctuations. Solar wind magnetic field fluctuations exhibit a complex multiscale nature, often encompassing ion-scale discontinuities and MHD-scale Alfvénic fluctuations. Both of these types of structures are thought to play a critical role in plasma heating and turbulence dissipation. Here we comparatively analyze the plasma pressure anisotropies within discontinuities and adjacent Alfvénic fluctuations, leveraging unique solar wind observations from orbit conjunctions between the ARTEMIS and WIND missions, along the same flow streamline, though about 150 Earth radii apart. Based on 11 cases of such observations, we compare direct measurements of plasma anisotropy from particle instruments with its estimates from anisotropic MHD theory using the ratios of correlated ion velocity and Alfvén speed variations ∆ v  i /∆ v A. We find that (1) sporadically observed discontinuities associated with bifurcated reconnection current sheets harbor significant parallel electron anisotropies of &gt;0.2; (2) direct electron measurements in all events reveal a median anisotropy of ~0.07 for Alfvénic fluctuations and ~0.17 for discontinuities; (3) anisotropic MHD predicts even more disparate total anisotropies within Alfvénic fluctuations and discontinuities, with a median value of ~0.15 for the former and ~0.57 for the latter; (4) the differences between theory-predicted and directly measured anisotropies imply that the ion contribution to anisotropy is significant and likely dominant within both types of structures, an assertion which we partly verify using simultaneous ion measurements from WIND. Our observations confirm that such discontinuities play a uniquely important role in producing solar wind plasma heating and anisotropy.

Keywords: Space plasmas, Solar magnetic reconnection, Heliosphere, Interplanetary turbulence, Interplanetary discontinuities, Solar wind, Interplanetary particle acceleration, Alfven waves, Solar magnetic fields
Star Formation Efficiency in Nearby Galaxies Revealed with a New CO-to-H<SUB>2</SUB> Conversion Factor Prescription. Determining how the galactic environment, especially the high gas densities and complex dynamics in bar-fed galaxy centers, alters the star formation efficiency (SFE) of molecular gas is critical to understanding galaxy evolution. However, these same physical or dynamical effects also alter the emissivity properties of CO, leading to variations in the CO-to-H2 conversion factor (α CO) that impact the assessment of the gas column densities and thus of the SFE. To address such issues, we investigate the dependence of α CO on the local CO velocity dispersion at 150 pc scales using a new set of dust-based α CO measurements and propose a new α CO prescription that accounts for CO emissivity variations across galaxies. Based on this prescription, we estimate the SFE in a sample of 65 galaxies from the PHANGS-Atacama Large Millimeter/submillimeter Array survey. We find increasing SFE toward high-surface-density regions like galaxy centers, while using a constant or metallicity-based α CO results in a more homogeneous SFE throughout the centers and disks. Our prescription further reveals a mean molecular gas depletion time of 700 Myr in the centers of barred galaxies, which is overall three to four times shorter than in nonbarred galaxy centers or the disks. Across the galaxy disks, the depletion time is consistently around 2-3 Gyr, regardless of the choice of α CO prescription. All together, our results suggest that the high level of star formation activity in barred centers is not simply due to an increased amount of molecular gas, but also to an enhanced SFE compared to nonbarred centers or disk regions.

Keywords: Disk galaxies, Galaxy nuclei, Giant molecular clouds, Star formation, CO line emission
Fine-structure Transitions of Ne<SUP>+</SUP>, Ar<SUP>+</SUP>, Ne<SUP>2+</SUP>, and Ar<SUP>2+</SUP> Induced by Collisions with Atomic Hydrogen. We calculate cross sections for fine-structure transitions of Ne+, Ar+, Ne2+, and Ar2+ in collisions with atomic hydrogen by using quantum-mechanical methods. Relaxation rate coefficients are calculated for temperatures up to 10,000 K. The temperature-dependent critical densities for the relaxation of Ne+, Ar+, Ne2+, and Ar2+ in collisions with H have been determined and compared to the critical densities for collisions with electrons. The present calculations will be useful for studies utilizing the infrared lines [Ne II] 12.8, [Ne III] 15.6, [Ne III] 36.0, [Ar II] 6.99, [Ar III] 8.99, and [Ar III] 21.8 μm as diagnostics of, for example, planetary nebulae and star formation.

Keywords: Atomic physics
Mapping Obscured Star Formation in the Host Galaxy of FRB 20201124A. We present high-resolution 1.5-6 GHz Karl G. Jansky Very Large Array and Hubble Space Telescope (HST) optical and infrared observations of the extremely active repeating fast radio burst (FRB) FRB 20201124A and its barred spiral host galaxy. We constrain the location and morphology of star formation in the host and search for a persistent radio source (PRS) coincident with FRB 20201124A. We resolve the morphology of the radio emission across all frequency bands and measure a star formation rate (SFR) ≈ 8.9 M ⊙ yr-1, approximately ≈2.5-6 times larger than optically inferred SFRs, demonstrating dust-obscured star formation throughout the host. Compared to a sample of all known FRB hosts with radio emission, the host of FRB 20201124A has the most significantly obscured star formation. While HST observations show the FRB to be offset from the bar or spiral arms, the radio emission extends to the FRB location. We propose that the FRB progenitor could have formed in situ (e.g., a magnetar born from a massive star explosion). It is still plausible, although less likely, that the progenitor of FRB 20201124A migrated from the central bar of the host. We further place a limit on the luminosity of a putative PRS at the FRB position of L 6.0GHz ≲ 1.8 ×1027 erg s-1 Hz-1, among the deepest PRS luminosity limits to date. However, this limit is still broadly consistent with both magnetar nebulae and hypernebulae models assuming a constant energy injection rate of the magnetar and an age of ≳105 yr in each model, respectively.

Keywords: Magnetars, Star formation, Radio transient sources
Searching for Associations between Short Gamma-Ray Bursts and Fast Radio Bursts. The physical origin of fast radio bursts (FRBs) is still unclear. However, young magnetars associated with short-duration gamma-ray bursts (SGRBs) have been thought to be possible central engines for some FRBs. In this paper, we perform a systematic search for SGRBs that are associated with FRBs in a sample including 623 FRBs (601 one-off bursts and 22 repeaters) and 168 SGRBs with precise localizations. We find that FRB 190309A is spatially associated with GRB 060502B, with a chance probability of 0.05 when temporal and redshift information is taken into account. Considering the high chance probability (the statistical significance is &lt;3σ), we examine other observational properties such as the host galaxy, the dispersion measure, and the energy budget of the central engine to check the possibility of their association. Although the available observational information is insufficient to determine whether they are physically associated, it does not rule out such a possibility. As the only pair of FRB and GRB that are spatially associated, it remains an interesting case worthy of further attention.

Keywords: Magnetars, Gamma-ray bursts, Radio transient sources