adsabs/SciX_UAT_keywords huggingface dataset:
A Systematic Observational Study on Galactic Interstellar Ratio 18O/17O. II. C18O and C17O J = 2-1 Data Analysis

To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace the chemical evolution of the Galaxy, we have performed a systematic study of Galactic interstellar 18O/17O ratios toward a sample of 421 molecular clouds with IRAM 30 m and the 10 m Submillimeter Telescope, covering a galactocentric distance range of ~1-22 kpc. The results presented in this paper are based on the J = 2-1 transition and encompass 364 sources showing both C18O and C17O detections. The previously suggested 18O/17O gradient is confirmed. For the 41 sources detected with both facilities, good agreement is obtained. A correlation of the 18O/17O ratios with heliocentric distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18O/17O = (0.12 ± 0.02)R GC + (2.38 ± 0.13) with a correlation coefficient of R = 0.67. While the slope is consistent with our J = 1-0 measurement, the ratios are systematically lower. This should be caused by larger optical depths of C18O 2-1 lines with respect to the corresponding 1-0 transitions, which is supported by RADEX calculations and the fact that C18O/C17O is positively correlated with 13CO/C18O. When we consider that optical depth effects with C18O J = 2-1 typically reach an optical depth of ~0.5, the corrected 18O/17O ratios from the J = 1-0 and J = 2-1 lines are consistent. A good numerical fit to the data is provided by the MWG-12 model, which includes both rotating stars and novae.

Keywords: interstellar molecules; radio source counts; isotopic abundances; galaxy chemical evolution
Deblending Galaxies with Generative Adversarial Networks

Deep generative models including generative adversarial networks (GANs) are powerful unsupervised tools in learning the distributions of data sets. Building a simple GAN architecture in PyTorch and training on the CANDELS data set, we generate galaxy images with the Hubble Space Telescope (HST) resolution starting from a noise vector. We proceed by modifying the GAN architecture to improve Subaru Hyper Suprime-Cam (HSC) ground-based images by increasing their resolution to the HST resolution. We use the super-resolution GAN on a large sample of blended galaxies, which we create using CANDELS cutouts. In our simulated blend sample, ~20% would unrecognizably be blended even in the HST-resolution cutouts. In the HSC-like cutouts this fraction rises to ~90%. With our modified GAN we can lower this value to ~50%. We quantify the blending fraction in the high, low, and GAN resolutions over the whole manifold of angular separation, flux ratios, sizes, and redshift difference between the two blended objects. The two peaks found by the GAN deblender result in improvement by a factor of 10 in the photometry measurement of the blended objects. Modifying the architecture of the GAN, we also train a multiwavelength GAN with HST cutouts in seven optical + near-infrared bands. This multiwavelength GAN improves the fraction of detected blends by another ~10% compared to the single-band GAN. This is most beneficial to the current and future precision cosmology experiments (e.g., LSST, SPHEREx, Euclid, Roman), specifically those relying on weak gravitational lensing, where blending is a major source of systematic error.

Keywords: convolutional neural networks; weak gravitational lensing; observational astronomy; galaxy photometry
Large Impact of the Mg II h and k Incident Radiation Change on Results of Radiative Transfer Models and the Importance of Dynamics

We demonstrate that changes in the incident radiation in Mg II h and k lines have a significant impact on the results of radiative transfer modeling of prominence-like plasmas. To uncover the extent of this impact and allow easy comparison, here we study two cases, one representing the minimum of the solar activity and the other corresponding to the typical conditions during solar maxima. To represent well the properties of the prominence plasma, we use the 2D non-LTE (i.e., departures from local thermodynamic equilibrium) model of prominence fine structures in both the single-thread configuration and the multithread configuration incorporating prominence dynamics. We show that in the modeled environment of prominence fine structures, the change in the central, integrated, and peak intensities of the synthetic Mg II h and k profiles can be as large as the change in the incident radiation itself. This means that the Mg II h and k spectra of observed prominences can be affected by tens of percent because the illumination from the solar disk can change by such a degree over the solar cycle. That makes the knowledge and use of event-specific incident radiation data very important for the diagnostics of prominences and other chromospheric and coronal structures when using Mg II h and k spectral observations. In addition, the observed Mg II h and k spectra are strongly influenced by the line-of-sight dynamics, as the multithread configuration of the 2D model allows us to reveal. The effect of dynamics is, unsurprisingly, most pronounced in the line widths and integrated intensities.

Keywords: solar prominences; solar cycle; solar ultraviolet emission; solar spectral irradiance
Exploring Proxies for the Supermassive Black Hole Mass Function: Implications for Pulsar Timing Arrays

Supermassive black holes (SMBHs) reside at the center of every massive galaxy in the local universe with masses that closely correlate with observations of their host galaxy, implying a connected evolutionary history. The population of binary SMBHs, which form following galaxy mergers, is expected to produce a gravitational-wave background (GWB) detectable by pulsar timing arrays (PTAs). PTAs are starting to see hints of what may be a GWB, and the amplitude of the emerging signal is toward the higher end of model predictions. Simulated populations of binary SMBHs can be constructed from observations of galaxies and are used to make predictions about the nature of the GWB. The greatest source of uncertainty in these observation-based models comes from the inference of the SMBH mass function, which is derived from observed host galaxy properties. In this paper, I undertake a new approach for inferring the SMBH mass function, starting from a velocity dispersion function rather than a galaxy stellar mass function. I argue that this method allows for a more direct inference by relying on a larger suite of individual galaxy observations as well as relying on a more "fundamental" SMBH mass relation. I find that the resulting binary SMBH population contains more massive systems at higher redshifts than previous models. Additionally, I explore the implications for the detection of individually resolvable sources in PTA data.

Keywords: supermassive black holes; galaxy mergers; gravitational waves; gravitational wave sources
Solar Energetic Particle Events with Short and Long Onset Times

Gradual solar energetic particle (SEP) events, usually attributed to shock waves driven by coronal mass ejections (CMEs), show a wide variety of temporal behaviors. For example, TO, the >10 MeV proton onset time with respect to the launch of the CME, has a distribution of at least an order of magnitude, even when the source region is not far from the so-called well-connected longitudes. It is important to understand what controls TO, especially in the context of space weather prediction. Here we study two SEP events from the western hemisphere that are different in TO on the basis of >10 MeV proton data from the Geostationary Operations Environmental Satellite, despite being similar in the CME speed and longitude of the source regions. We try to find the reasons for different TO, or proton release times, in how the CME-driven shock develops and the Alfvén Mach number of the shock wave reaches some threshold by combining the CME height-time profiles with radio dynamic spectra. We also discuss how CME-CME interactions and active region properties may affect the proton release times.

Keywords: solar energetic particles; solar coronal mass ejections; solar coronal mass ejection shocks; space weather
PHANGS-ML: Dissecting Multiphase Gas and Dust in Nearby Galaxies Using Machine Learning

The PHANGS survey uses Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, Very Large Telescope, and JWST to obtain an unprecedented high-resolution view of nearby galaxies, covering millions of spatially independent regions. The high dimensionality of such a diverse multiwavelength data set makes it challenging to identify new trends, particularly when they connect observables from different wavelengths. Here, we use unsupervised machine-learning algorithms to mine this information-rich data set to identify novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we extract properties pertaining to their stellar populations; warm ionized and cold molecular gas; and polycyclic aromatic hydrocarbons (PAHs), as measured over 150 pc scale regions. We show that we can divide the regions into groups with distinct multiphase gas and PAH properties. In the process, we identify previously unknown galaxy-wide correlations between PAH band and optical line ratios and use our identified groups to interpret them. The correlations we measure can be naturally explained in a scenario where the PAHs and the ionized gas are exposed to different parts of the same radiation field that varies spatially across the galaxies. This scenario has several implications for nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests significant self-regulation in the interstellar medium, (ii) the PAH 11.3/7.7 μm band ratio may be used to constrain the shape of the non-ionizing far-ultraviolet to optical part of the radiation field, and (iii) the varying radiation field affects line ratios that are commonly used as PAH size diagnostics. Neglecting this effect leads to incorrect or biased PAH sizes.

Keywords: astrostatistics techniques; astronomy data visualization; warm ionized medium; interstellar dust; polycyclic aromatic hydrocarbons
The Cosmic-Ray Composition between 2 PeV and 2 EeV Observed with the TALE Detector in Monocular Mode

We report on a measurement of the cosmic-ray composition by the Telescope Array Low-energy Extension (TALE) air fluorescence detector (FD). By making use of the Cherenkov light signal in addition to air fluorescence light from cosmic-ray (CR)-induced extensive air showers, the TALE FD can measure the properties of the cosmic rays with energies as low as ∼2 PeV and exceeding 1 EeV. In this paper, we present results on the measurement of ${X}_{\max }$ <!-- --> distributions of showers observed over this energy range. Data collected over a period of ∼4 yr were analyzed for this study. The resulting ${X}_{\max }$ <!-- --> distributions are compared to the Monte Carlo (MC) simulated data distributions for primary cosmic rays with varying composition and a four-component fit is performed. The comparison and fit are performed for energy bins, of width 0.1 or 0.2 in ${\mathrm{log}}_{10}(E/\mathrm{eV})$ <!-- --> ,spanning the full range of the measured energies. We also examine the mean ${X}_{\max }$ <!-- --> value as a function of energy for cosmic rays with energies greater than 1015.8 eV. Below 1017.3 eV, the slope of the mean ${X}_{\max }$ <!-- --> as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the models, indicating that the composition is becoming heavier with energy in this energy range. This is consistent with a rigidity-dependent cutoff of events from Galactic sources. Finally, an increase in the ${X}_{\max }$ <!-- --> elongation rate is observed at energies just above 1017 eV, indicating another change in the cosmic-ray composition.

Keywords: cosmic rays; cosmic ray showers; cosmic ray detectors; particle astrophysics
General Physical Properties of Fermi Blazars

We study the general physical properties of Fermi blazars using the Fermi fourth source catalog data (4FGL-DR2). The quasi-simultaneous multiwavelength data of Fermi blazars are fitted by using the one-zone leptonic model to obtain some physical parameters, such as jet power, magnetic field, and Doppler factor. We study the distributions of the derived physical parameters as a function of black hole mass and accretion disk luminosity. The main results are as follows. (1) For a standard thin accretion disk, the jet kinetic power of most flat-spectrum radio quasars can be explained by the Blandford-Payne (BP) mechanism. However, the jet kinetic power of most BL Lacertae objects (BL Lacs) cannot be explained by either the Blandford-Znajek mechanism or the BP mechanism. The BL Lacs may have advection-dominated accretion flows surrounding their massive black holes. (2) After excluding the redshift, there is a moderately strong correlation between the jet kinetic power and jet radiation power and the accretion disk luminosity for Fermi blazars. These results confirm a close connection between jet and accretion. The jet kinetic power is slightly larger than the accretion disk luminosity for Fermi blazars. (3) There is a significant correlation between jet kinetic power and gamma-ray luminosity and radio luminosity for Fermi blazars, which suggests that gamma-ray luminosity and radio luminosity can be used to indicate the jet kinetic power.

Keywords: active galactic nuclei; gamma-rays; gamma-ray sources; bl lacertae objects; flat-spectrum radio quasars; jets
Seismological Studies of Pulsating DA White Dwarfs Observed with the Kepler Space Telescope and K2 Campaigns 1-8

AllS single stars that are born with masses up to 8.5-10 M ⊙ will end their lives as white dwarf (WD) stars. In this evolutionary stage, WDs enter the cooling sequence, where the stars radiate away their thermal energy and are basically cooling. As these stars cool, they reach temperatures and conditions that cause the stars to pulsate. Using differential photometry to produce light curves, we can determine the observed periods of pulsation from the WD. We used the White Dwarf Evolution Code (WDEC) to calculate a grid of over one million models with various temperature, stellar mass, and mass of helium and hydrogen layers and calculated their theoretical pulsation periods. In this paper, we describe our approach to WD asteroseismology using WDEC models, and we present seismological studies for 29 observed DAVs in the Kepler and K2 data sets, 25 of which have never been analyzed using these observations and 19 of which have never been seismically analyzed in any capacity before. Learning about the internal structure of WDs places important constraints on the WD cooling sequence and our overall understanding of stellar evolution for low-mass stars.

Keywords: white dwarf stars; asteroseismology; variable stars
Nucleosynthesis in the Innermost Ejecta of Magnetorotational Supernova Explosions in Three Dimensions

Core-collapse supernova (CCSN) explosions powered by rotation and magnetic fields present an interesting astrophysical site for nucleosynthesis that potentially contributes to the production of r-process elements. Here we present yields of the innermost ejecta in 3D magnetorotational CCSN models simulated using the COCONUT-FMT code. Strong magnetic fields tap the rotational energy of the proto‑neutron star and lead to earlier and more energetic (∼3 × 1051 erg) explosions than typical neutrino-driven CCSNe. Compared to a reference nonmagnetic model, the ejecta in the magnetorotational models have much more neutron-rich components with Y e down to ∼0.25. Our post-processing calculations with the reaction network SkyNet show significant production of weak r-process elements up to mass number ∼130. We find negligible differences in the synthesis of heavy elements between two magnetorotational models with different initial field strengths of 1010 and 1012 G, in accord with their similar explosion dynamics. The magnetorotational models produce about ∼0.19 and 0.14 M ☉ of radioactive 56Ni, on the low end of inferred hypernova nickel masses. The yields are publicly available at Zenodo (doi: 10.5281/zenodo.10578981) for comparison with stellar abundance patterns, inclusion in modeling galactic chemical evolution, and comparison with other yield calculations. Our results add to the yet-restricted corpus of nucleosynthesis yields from 3D magnetorotational supernova simulations and will help quantify yield uncertainties.

Keywords: core-collapse supernovae; magnetohydrodynamics; nucleosynthesis; r-process
Optical Properties of Cyanoacetylene Ices in the Far- to Near-infrared with Direct Relevance to Titan's Stratospheric Ice Clouds

Cyanoacetylene (HC3N) ice has been observed in Titan's stratosphere by both Voyager 1's InfraRed Interferometer Spectrometer (IRIS) and Cassini's Composite InfraRed Spectrometer (CIRS), and it is likely prevalent in other objects in our solar system and exoplanetary systems as well. While previous experimental studies targeting Titan's stratospheric clouds have determined the optical properties of HC3N ice in the infrared (IR) spectral range, those thin ice films were formed by annealing processes, which contradicts the formation mechanism of Titan's stratospheric ice clouds. As a result, optical constants of HC3N ices, experimentally created in a similar manner to the way they are formed in Titan's stratosphere, are crucial. Here we experimentally measured absorbance spectra of HC3N thin ice films from the near- to far-IR spectral region (50-8000 cm-1; 200-1.25 μm) formed via direct vapor deposition at 30, 50, 70, 90, 110, and 113 K. The corresponding optical constants at all temperatures were also computed, resulting in the largest continuous IR spectral range available for HC3N ice. New tentative peak assignments for spectral features in the near-IR are also reported, thereby further enhancing the inventory of optical constants available for HC3N ice spanning the near- to far-IR spectral range.

Keywords: planetary atmospheres; atmospheric clouds; radiative transfer; titan
Stephan Prantner's Sunspot Observations during the Dalton Minimum

In addition to regular Schwabe cycles (≈11 yr), solar variability also shows longer periods of enhanced or reduced activity. Of these, reconstructions of the Dalton Minimum provide controversial sunspot group numbers and limited sunspot positions, partially due to limited source record accessibility. In this context, we analyzed Stephan Prantner's sunspot observations spanning from 1804 to 1844, the values of which had only been known through estimates despite their notable chronological coverage during the Dalton Minimum. We identified his original manuscript in Stiftsarchiv Wilten, near Innsbruck (Austria). We reviewed his biography (1782-1873) and located his observational sites at Wilten and Waidring, which housed the principal telescopes for his early and late observations: a 3.5 inch astronomical telescope and a Reichenbach 4 foot achromatic erecting telescope, respectively. We identified 215 days of datable sunspot observations, which is almost twice as much data as his estimated data in the existing databases (=115 days). In Prantner's records, we counted up to seven to nine sunspot groups per day and measured sunspot positions, which show their distributions in both solar hemispheres. These results strikingly emphasize the difference between the Dalton Minimum and the Maunder Minimum as well as the similarity between the Dalton Minimum and the weak solar cycles in the modern observations.

Keywords: sunspots; sunspot cycle; sunspot groups; solar-terrestrial interactions; maunder minimum
A Machine Learning Approach to Understanding the Physical Properties of Magnetic Flux Ropes in the Solar Wind at 1 au

Interplanetary magnetic flux ropes (MFRs) are commonly observed structures in the solar wind, categorized as magnetic clouds (MCs) and small-scale MFRs (SMFRs) depending on whether they are associated with coronal mass ejections. We apply machine learning to systematically compare SMFRs, MCs, and ambient solar wind plasma properties. We construct a data set of 3-minute averaged sequential data points of the solar wind's instantaneous bulk fluid plasma properties using about 20 years of measurements from Wind. We label samples by the presence and type of MFRs containing them using a catalog based on Grad-Shafranov (GS) automated detection for SMFRs and NASA's catalog for MCs (with samples in neither labeled non-MFRs). We apply the random forest machine learning algorithm to find which categories can be more easily distinguished and by what features. MCs were distinguished from non-MFRs with an area under the receiver-operator curve (AUC) of 94% and SMFRs with an AUC of 89%, and had distinctive plasma properties. In contrast, while SMFRs were distinguished from non-MFRs with an AUC of 86%, this appears to rely solely on the > 5 nT threshold applied by the GS catalog. The results indicate that SMFRs have virtually the same plasma properties as the ambient solar wind, unlike the distinct plasma regimes of MCs. We interpret our findings as additional evidence that most SMFRs at 1 au are generated within the solar wind. We also suggest that they should be considered a salient feature of the solar wind's magnetic structure rather than transient events.

Keywords: solar wind; heliosphere; random forests
The Stellar Halo of the Galaxy is Tilted and Doubly Broken

Modern Galactic surveys have revealed an ancient merger that dominates the stellar halo of our galaxy (Gaia-Sausage-Enceladus, GSE). Using chemical abundances and kinematics from the H3 Survey, we identify 5559 halo stars from this merger in the radial range r Gal = 6-60kpc. We forward model the full selection function of H3 to infer the density profile of this accreted component of the stellar halo. We consider a general ellipsoid with principal axes allowed to rotate with respect to the galactocentric axes, coupled with a multiply broken power law. The best-fit model is a triaxial ellipsoid (axes ratios 10:8:7) tilted 25° above the Galactic plane toward the Sun and a doubly broken power law with breaking radii at 12 kpc and 28 kpc. The doubly broken power law resolves a long-standing dichotomy in literature values of the halo breaking radius, being at either ~15 kpc or ~30 kpc assuming a singly broken power law. N-body simulations suggest that the breaking radii are connected to apocenter pile-ups of stellar orbits, and so the observed double-break provides new insight into the initial conditions and evolution of the GSE merger. Furthermore, the tilt and triaxiality of the stellar halo could imply that a fraction of the underlying dark matter halo is also tilted and triaxial. This has important implications for dynamical mass modeling of the galaxy as well as direct dark matter detection experiments.

Keywords: milky way stellar halo; milky way dark matter halo; galaxy dark matter halos; milky way galaxy physics