adsabs/SciX_UAT_keywords huggingface dataset:
Technique for Separating Velocity and Density Contributions in Spectroscopic Data and Its Application to Studying Turbulence and Magnetic Fields

Based on the theoretical description of position-position-velocity (PPV) statistics in Lazarian & Pogosyan, we introduce a new technique called the velocity decomposition algorithm (VDA) for separating the PPV fluctuations arising from velocity and density fluctuations. Using MHD turbulence simulations, we demonstrate its promise in retrieving the velocity fluctuations from the PPV cube in various physical conditions and its prospects in accurately tracing the magnetic field. We find that for localized clouds, the velocity fluctuations are most prominent in the wing part of the spectral line, and they dominate the density fluctuations. The same velocity dominance applies to extended H I regions undergoing galactic rotation. Our numerical experiment demonstrates that velocity channels arising from the cold phase of atomic hydrogen (H I) are still affected by velocity fluctuations at small scales. We apply the VDA to H I GALFA-DR2 data corresponding to the high-velocity cloud HVC186+19-114 and high-latitude galactic diffuse H I data. Our study confirms the crucial role of velocity fluctuations in explaining why linear structures are observed within PPV cubes. We discuss the implications of VDA for both magnetic field studies and predicting polarized galactic emission that acts as the foreground for cosmic microwave background studies. Additionally, we address the controversy related to the filamentary nature of the H I channel maps and explain the importance of velocity fluctuations in the formation of structures in PPV data cubes. VDA will allow astronomers to obtain velocity fluctuations from almost every piece of spectroscopic PPV data and allow direct investigations of the turbulent velocity field in observations.

Keywords: interstellar magnetic fields; interstellar medium; interstellar dynamics; interstellar atomic gas; interstellar filaments
A Study of Primordial Very Massive Star Evolution

We present new evolutionary models of primordial very massive stars with initial masses ranging from 100 to 1000 M ⊙ that extend from the main sequence to the onset of dynamical instability caused by the creation of electron-positron pairs during core C, Ne, or O burning, depending on the star's mass and metallicity. Mass loss accounts for radiation-driven winds, as well as pulsation-driven mass loss on the main sequence and during the red supergiant phase. After examining the evolutionary properties, we focus on the final outcome of the models and associated compact remnants. Stars that avoid the pair instability supernova channel should produce black holes with masses ranging from ≈40 to ≈1000 M ⊙. In particular, stars with initial masses of about 100 M ⊙ could leave black holes of ≃85-90 M ⊙, values consistent with the estimated primary black hole mass of the GW190521 merger event. Overall, these results may contribute to explaining future data from next-generation gravitational-wave detectors, such as the Einstein Telescope and Cosmic Explorer, which will have access to an as-yet-unexplored black hole mass range of ≈102-104 M ⊙ in the early universe.

Keywords: stellar evolution; stellar remnants; stellar winds; population iii stars
Solar Flare Index Prediction Using SDO/HMI Vector Magnetic Data Products with Statistical and Machine-learning Methods

Solar flares, especially the M- and X-class flares, are often associated with coronal mass ejections. They are the most important sources of space weather effects, which can severely impact the near-Earth environment. Thus it is essential to forecast flares (especially the M- and X-class ones) to mitigate their destructive and hazardous consequences. Here, we introduce several statistical and machine-learning approaches to the prediction of an active region's (AR) flare index (FI) that quantifies the flare productivity of an AR by taking into account the number of different class flares within a certain time interval. Specifically, our sample includes 563 ARs that appeared on the solar disk from 2010 May to 2017 December. The 25 magnetic parameters, provided by the Space-weather HMI Active Region Patches (SHARP) from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, characterize coronal magnetic energy stored in ARs by proxy and are used as the predictors. We investigate the relationship between these SHARP parameters and the FI of ARs with a machine-learning algorithm (spline regression) and the resampling method (Synthetic Minority Oversampling Technique for Regression with Gaussian Noise). Based on the established relationship, we are able to predict the value of FIs for a given AR within the next 1 day period. Compared with other four popular machine-learning algorithms, our methods improve the accuracy of FI prediction, especially for a large FI. In addition, we sort the importance of SHARP parameters by the Borda count method calculated from the ranks that are rendered by nine different machine-learning methods.

Keywords: solar flares; solar physics; solar activity
On the Random Motion of Nuclear Objects in a Fuzzy Dark Matter Halo

Fuzzy dark matter (FDM), consisting of ultralight bosons ( ${m}_{{\rm{b}}}\sim {10}^{-22}\,\,\mathrm{eV}$ ), is an intriguing alternative to cold dark matter. Numerical simulations that solve the Schrödinger-Poisson (SP) equation show that FDM halos consist of a central solitonic core, which is the ground state of the SP equation, surrounded by an envelope of interfering excited states. These excited states also interfere with the soliton, causing it to oscillate and execute a confined random walk with respect to the halo center of mass. Using high-resolution numerical simulations of a $6.6\times {10}^{9}\,\,{M}_{\odot }$ FDM halo with ${m}_{{\rm{b}}}=8\times {10}^{-23}\,\,\mathrm{eV}$ in isolation, we demonstrate that the wobbling, oscillating soliton gravitationally perturbs nuclear objects, such as supermassive black holes or dense star clusters, causing them to diffuse outwards. In particular, we show that, on average, objects with mass ≲0.3% of the soliton mass ( ${M}_{\mathrm{sol}}$ ) are expelled from the soliton in ~3 $\,\mathrm{Gyr}$ , after which they continue their outward diffusion due to gravitational interactions with the soliton and the halo granules. More massive objects (≳ $1 \% \,{M}_{\mathrm{sol}}$ ), while executing a random walk, remain largely confined to the soliton due to dynamical friction. We also present an effective treatment of the diffusion, based on kinetic theory, that accurately reproduces the outward motion of low-mass objects and briefly discuss how the observed displacements of star clusters and active galactic nuclei from the centers of their host galaxies can be used to constrain FDM.

Keywords: galaxy nuclei; galaxy dynamics; galaxy dark matter halos; gravitational interaction; dynamical friction; supermassive black holes
A Comprehensive Analysis of NGC 2158 in the Gaia Era: Photometric Parameters, Apex, and Orbit

We present an investigation of NGC 2158 using Gaia DR2 data. We identified 800 most likely cluster members with membership probability higher than 90%. The mean proper motions of this object are determined as (μx = -0.203 ± 0.003, μy = -1.99 ± 0.004) mas yr-1. The limiting radius, log(age), and distance of the cluster are obtained as 23.5 arcmin, 9.38 ± 0.04 Gyr, and 4.69 ± 0.22 kpc, respectively. The overall mass function slope (0.93 ± 0.14) is flatter than the Salpeter value (1.35) within the mass range of 1.17-1.44 M⊙. This cluster also shows the mass-segregation effect and our study demonstrates that NGC 2158 is a dynamically relaxed open cluster. Using the apex diagram (AD), the apex coordinates of the cluster are obtained in different ways and are examined using the (μU,μT) diagram. The best value of the apex coordinates is determined as A = 87°24 ± 1°60, D = -36°61 ± 5°30. We also determined the orbit of the cluster and found that NGC 2158 moves almost in the solar antapex direction. The resulting spatial velocity of NGC 2158 is 51 km s-1. A significant oscillation along the Z-coordinate up to 529 pc is detected. Various scenarios regarding the origin of this cluster are also discussed.

Keywords: s stars; hertzsprung russell diagram; open star clusters; astrometry; stellar kinematics; apex; orbit determination
The FLASHES Survey. I. Integral Field Spectroscopy of the CGM around 48 z ≃ 2.3-3.1 QSOs

We present the pilot study of the Fluorescent Lyman-Alpha Structures in High-z Environments Survey; the largest integral field spectroscopy survey to date of the circumgalactic medium at z = 2.3-3.1. We observed 48 quasar fields with the Palomar Cosmic Web Imager to an average (2σ) limiting surface brightness of 6 × 10-18 erg s-1 cm-2 arcsec-2 (in a 1″ aperture and ∼20 Å bandwidth). Extended H I Lyα emission is discovered around 37/48 of the observed quasars, ranging in projected radius from 14 to 55 proper kiloparsecs (pkpc), with one nebula exceeding 100 pkpc in effective diameter. The dimming-adjusted circularly averaged surface brightness profile peaks at 1 × 10-15 erg s-1 cm-2 arcsec-2 at R⊥ ∼ 20 pkpc and integrated luminosities range from 0.4 to 9.4 × 1043 erg s-1. The emission appears to have an eccentric morphology and an average covering factor of ∼30%-40% at small radii. On average, the nebular spectra are redshifted with respect to both the systemic redshift and Lyα peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single- or double-peaked profiles with global dispersions ranging from 143 to 708 km s-1, though the individual Gaussian components of lines with complex shapes mostly have dispersions ≤400 km s-1, and the flux-weighted velocity centroids of the lines vary by thousands of km s-1 with respect to the QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with those expected from gravitational motions in dark matter halos of mass ${\mathrm{Log}}_{10}({M}_{{\rm{h}}}[{M}_{\odot }])\simeq {12.2}_{-1.2}^{+0.7}$ Log 10 ( M h [ M ⊙ ] ) ≃ 12.2 - 1.2 + 0.7 . We compare these results to existing surveys at higher and lower redshift.

Keywords: galaxies; galaxy evolution; circumgalactic medium; intergalactic medium; quasars; galaxy environments
A Search for Transiting Planets in the Globular Cluster M4 with K2: Candidates and Occurrence Limits

We perform a search for transiting planets in the NASA K2 observations of the globular cluster (GC) M4. This search is sensitive to larger orbital periods (P ≲ 35 days, compared to the previous best of P ≲ 16 days), and at the shortest periods, smaller planet radii (Rp ≳ 0.3 RJ, compared to the previous best of Rp ≳ 0.8 RJ) than any previous search for GC planets. Seven planet candidates are presented. An analysis of the systematic noise in our data shows that most, if not all, of these candidates are likely false alarms. We calculate planet occurrence rates assuming our highest significance candidate is a planet and occurrence rate upper limits assuming no detections. We calculate 3σ occurrence rate upper limits of 6.1% for 0.71-2 RJ planets with 1-36 days periods and 16% for 0.36-0.71 RJ planets with 1-10 days periods. The occurrence rates from Kepler, TESS, and radial velocity studies of field stars are consistent with both a nondetection of a planet and detection of a single hot Jupiter in our data. Comparing to previous studies of GCs, we are unable to place a more stringent constraint than Gilliland et al. for the radius-period range they were sensitive to, but do place tighter constraints than both Weldrake et al. and Nascimbeni et al. for the large-radius regimes to which they were sensitive.

Keywords: exoplanets; globular star clusters; hot jupiters; transit photometry
Dynamical Stellar Masses of Pre-main-sequence Stars in Lupus and Taurus Obtained with ALMA Surveys in Comparison with Stellar Evolutionary Models

We analyzed archival molecular line data of pre-main-sequence (PMS) stars in the Lupus and Taurus star-forming regions obtained with ALMA surveys with an integration time of a few minutes per source. We stacked the data of 13CO and C18O (J = 2-1 and 3-2) and CN (N = 3-2, J = 7/2-5/2) lines to enhance the signal-to-noise ratios and measured the stellar masses of 45 out of 67 PMS stars from the Keplerian rotation in their circumstellar disks. The measured dynamical stellar masses were compared to the stellar masses estimated from the spectroscopic measurements with seven different stellar evolutionary models. We found that the magnetic model of Feiden provides the best estimate of the stellar masses in the mass range of 0.6 M⊙ ≤ M⋆ ≤ 1.3 M⊙ with a deviation of <0.7σ from the dynamical masses, while all the other models underestimate the stellar masses in this mass range by 20%-40%. In the mass range of <0.6 M⊙, the stellar masses estimated with the magnetic model of Feiden have a larger deviation (>2σ) from the dynamical masses, and other, nonmagnetic stellar evolutionary models of Siess et al., Baraffe et al., and Feiden show better agreement with the dynamical masses with the deviations of 1.4σ-1.6σ. Our results show the mass dependence of the accuracy of these stellar evolutionary models.

Keywords: pre-main sequence stars; circumstellar disks; stellar masses; stellar evolutionary models
3D Morphology of Open Clusters in the Solar Neighborhood with Gaia EDR 3: Its Relation to Cluster Dynamics

We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located within 500 pc of the Sun, using Gaia EDR 3 and kinematic data from the literature. Members of OCs are identified using the unsupervised machine-learning method StarGO, using five parameters (X, Y, Z, ${\mu }_{\alpha }\cos \delta ,{\mu }_{\delta }$ ). The OC sample covers an age range of 25 Myr to 2.65 Gyr. We correct the asymmetric distance distribution that is due to parallax error using Bayesian inversion. The uncertainty in the corrected distance for a cluster at 500 pc is 3.0-6.3 pc, depending on the intrinsic spatial distribution of its members. We determine the 3D morphology of the OCs in our sample and fit the spatial distribution of stars within the tidal radius in each cluster with an ellipsoid model. The shapes of the OCs are well described with oblate spheroids (NGC 2547, NGC 2516, NGC 2451A, NGC 2451B, and NGC 2232), prolate spheroids (IC 2602, IC 4665, NGC 2422, Blanco 1, and Coma Berenices), or triaxial ellipsoids (IC 2391, NGC 6633, and NGC 6774). The semimajor axis of the fitted ellipsoid is parallel to the Galactic plane for most clusters. Elongated filament-like substructures are detected in three young clusters (NGC 2232, NGC 2547, and NGC 2451B), while tidal-tail-like substructures (tidal tails) are found in older clusters (NGC 2516, NGC 6633, NGC 6774, Blanco 1, and Coma Berenices). Most clusters may be supervirial and expanding. N-body models of rapid gas expulsion with a star formation efficiency of ≈1/3 are consistent with clusters more massive than 250 M⊙, while clusters less massive than 250 M⊙ tend to agree with adiabatic gas expulsion models. Only five OCs (NGC 2422, NGC 6633, NGC 6774, Blanco 1, and Coma Berenices) show clear signs of mass segregation.

Keywords: star clusters; open star clusters; stellar dynamics
An Exquisitely Deep View of Quenching Galaxies through the Gravitational Lens: Stellar Population, Morphology, and Ionized Gas

This work presents an in-depth analysis of four gravitationally lensed red galaxies at z = 1.6-3.2. The sources are magnified by factors of 2.7-30 by foreground clusters, enabling spectral and morphological measurements that are otherwise challenging. Our sample extends below the characteristic mass of the stellar mass function and is thus more representative of the quiescent galaxy population at z > 1 than previous spectroscopic studies. We analyze deep VLT/X-SHOOTER spectra and multiband Hubble Space Telescope photometry that cover the rest-frame UV-to-optical regime. The entire sample resembles stellar disks as inferred from lensing-reconstructed images. Through stellar population synthesis analysis, we infer that the targets are young (median age = 0.1-1.2 Gyr) and formed 80% of their stellar masses within 0.07-0.47 Gyr. Mg II λλ 2796, 2803 absorption is detected across the sample. Blueshifted absorption and/or redshifted emission of Mg II are found in the two youngest sources, indicative of a galactic-scale outflow of warm (T ~ 104 K) gas. The [O III] λ5007 luminosity is higher for the two young sources (median age less than 0.4 Gyr) than the two older ones, perhaps suggesting a decline in nuclear activity as quenching proceeds. Despite high-velocity (v ≈ 1500 km s-1) galactic-scale outflows seen in the most recently quenched galaxies, warm gas is still present to some extent long after quenching. Altogether, our results indicate that star formation quenching at high redshift must have been a rapid process (<1 Gyr) that does not synchronize with bulge formation or complete gas removal. Substantial bulge growth is required if they are to evolve into the metal-rich cores of present-day slow rotators.

Keywords: galaxy evolution; galaxy processes; galaxy chemical evolution; galaxy quenching; galaxy structure; stellar populations; supermassive black holes; metallicity; warm ionized medium; active galactic nuclei; galaxy ages; galaxy stellar content
A Census of the Most Luminous Stars. I. The Upper HR Diagram for the Large Magellanic Cloud

Spectral classification and multiwavelength photometry for the most luminous stars in the LMC has greatly increased due to several recent surveys for both the hottest and coolest members. Combining data from these spectroscopic and photometric surveys, we have created catalogs based on their spectral classifications of the different groups: the luminous O and B stars, the A-type supergiants, and the evolved yellow and red supergiants. We derive their stellar parameters based on spectroscopic characteristics, and discuss the problems with extinction in crowded fields and the role of binarity on selected stars. Based on these surveys, we present the upper HR diagram representative of the LMC massive star population greater than 20 M ⊙.

Keywords: massive stars; large magellanic cloud
Connecting Primordial Star-forming Regions and Second-generation Star Formation in the Phoenix Simulations

We introduce the Phoenix Simulations, a suite of highly resolved cosmological simulations featuring hydrodynamics, primordial gas chemistry, primordial and enriched star formation and feedback, UV radiative transfer, and saved outputs with Δt = 200 kyr. We observe 73,523 individual primordial stars within 3313 distinct regions forming 2110 second-generation enriched star clusters by z ≥ 12 within a combined 177.25 Mpc3 volume across three simulations. The regions that lead to enriched star formation can contain ≳150 primordial stars, with 80% of regions having experienced combinations of primordial Type II, hypernovae, and/or pair-instability supernovae. Primordial supernovae enriched 0.8% of the volume, with 2% of enriched gas enriched by later-generation stars. We determine the extent of a primordial stellar region by its metal-rich or ionized hydrogen surrounding cloud; the metal-rich and ionized regions have time-dependent average radii r ≲ 3 kpc. 7 and 17% of regions have r > 7 kpc for metal-rich and ionized radii, respectively. We find that the metallicity distribution function of second-generation stars overlaps that of subsequent Population II star formation, spanning metal-deficient (~7.94 × 10-8 Z ⊙) to supersolar (~3.71 Z ⊙), and that 30.5% of second-generation stars have Z > 10-2 Z ⊙. We find that the metallicity of second-generation stars depends on progenitor configuration, with metals from pair-instability supernovae contributing to the most metal-rich clusters; these clusters form promptly after the supernova event. Finally, we create an interpretable regression model to predict the radius of the metal-rich influence of Population III star systems within the first 7-18 Myr after the first Population III stars form in the region.

Keywords: population iii stars; population ii stars; primordial galaxies; star forming regions
Composite Bulges. III. A Study of Nuclear Star Clusters in Nearby Spiral Galaxies

We present photometric and morphological analyses of nuclear star clusters (NSCs)-very dense, massive star clusters present in the central regions of most galaxies-in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3. We fit the images in 2D to take into account the full complexity of the inner regions of these galaxies (including the contributions of nuclear disks and bars), isolating the NSC and bulge components. We derive NSC radii and magnitudes in all three bands, which we then use to estimate NSC masses. Our sample significantly expands the sample of massive late-type galaxies with measured NSC properties. We clearly identify NSCs in nearly 80% of our galaxies, putting a lower limit on the nucleation fraction in these galaxies that is higher than previous estimates. We find that the NSCs in our massive disk galaxies are consistent with previous NSC mass-NSC radius and galaxy mass-NSC mass relations. However, we also find a large spread in NSC masses, with a handful of galaxies hosting very low-mass, compact clusters. Our NSCs are aligned in PA with their host galaxy disks but are less flattened. They show no correlations with bar or bulge properties. Finally, we find the ratio of NSC to BH mass in our massive disk galaxy sample spans a factor of ~300.

Keywords: disk galaxies; star clusters
Probing the Chemical Complexity of Amines in the ISM: Detection of Vinylamine (C2H3NH2) and Tentative Detection of Ethylamine (C2H5NH2)

Amines, particularly primary amines (R-NH2), are closely related to the primordial synthesis of amino acids since they share the same structural backbone. However, only a limited number of amines has been identified in the interstellar medium, which prevents us from studying their chemistry as well as their relation to prebiotic species that could lead to the emergence of life. In this Letter, we report the first interstellar detection of vinylamine (C2H3NH2) and tentative detection of ethylamine (C2H5NH2) toward the Galactic center cloud G+0.693-0.027. The derived abundance with respect to H2 is (3.3 ± 0.4) × 10-10 and (1.9 ± 0.5) × 10-10, respectively. The inferred abundance ratios of C2H3NH2 and C2H5NH2 with respect to methylamine (CH3NH2) are ~0.02 and ~0.008, respectively. The derived abundance of C2H3NH2, C2H5NH2, and several other NH2-bearing species are compared to those obtained toward high-mass and low-mass star-forming regions. Based on recent chemical and laboratory studies, possible chemical routes for the interstellar synthesis of C2H3NH2 and C2H5NH2 are discussed.

Keywords: pre-biotic astrochemistry; interstellar molecules; chemical abundances; galactic center