Sazuna/UAT_keywords huggingface dataset:
Early-type Host Galaxies of Type Ia Supernovae. II. Evidence for Luminosity Evolution in Supernova Cosmology. The most direct and strongest evidence for the presence of dark energy is provided by the measurement of galaxy distances using SNe Ia. This result is based on the assumption that the corrected brightness of SN Ia through the empirical standardization would not evolve with look-back time. Recent studies have shown, however, that the standardized brightness of SN Ia is correlated with host morphology, host mass, and local star formation rate (SFR), suggesting a possible correlation with stellar population property. To understand the origin of these correlations, we have continued our spectroscopic observations to cover most of the reported nearby early-type host galaxies. From high-quality (signal-to-noise ratio ∼175) spectra, we obtained the most direct and reliable estimates of population age and metallicity for these host galaxies. We find a significant correlation between SN luminosity (after the standardization) and stellar population age at a 99.5% confidence level. As such, this is the most direct and stringent test ever made for the luminosity evolution of SN Ia. Based on this result, we further show that the previously reported correlations with host morphology, host mass, and local SFR are most likely originated from the difference in population age. This indicates that the light-curve fitters used by the SNe Ia community are not quite capable of correcting for the population age effect, which would inevitably cause a serious systematic bias with look-back time. Notably, taken at face values, most of the Hubble residual used in the discovery of the dark energy appears to be affected by the luminosity evolution.

Keywords: Observational cosmology, Type Ia supernovae, Early-type galaxies, Dark energy
GASP. XXII. The Molecular Gas Content of the JW100 Jellyfish Galaxy at z ∼ 0.05: Does Ram Pressure Promote Molecular Gas Formation?. Within the GASP survey, aimed at studying the effect of ram pressure stripping on star formation quenching in cluster galaxies, we analyze here ALMA observations of the jellyfish galaxy JW100. We find an unexpected large amount of molecular gas (∼2.5 × 1010 ${M}_{\odot }$ ), 30% of which is located in the stripped gas tail out to ∼35 kpc from the galaxy center. The overall kinematics of the molecular gas is similar to the one shown by the ionized gas, but for clear signatures of double components along the stripping direction detected only out to 2 kpc from the disk. The line ratio r21 has a clumpy distribution and in the tail can reach large values (≥1), while its average value is low (0.58 with a 0.15 dispersion). All these evidence strongly suggest that the molecular gas in the tail is newly born from stripped H I gas or newly condensed from stripped diffuse molecular gas. The analysis of interferometric data at different scales reveals that a significant fraction (∼40%) of the molecular gas is extended over large scales (≥8 kpc) in the disk, and this fraction becomes predominant in the tail (∼70%). By comparing the molecular gas surface density with the star formation rate surface density derived from the Hα emission from MUSE data, we find that the depletion time on 1 kpc scale is particularly large (5-10 Gyr) both within the ram-pressure-disturbed region in the stellar disk and in the complexes along the tail.

Keywords: Galaxy clusters, Molecular gas, D galaxies, Galaxy evolution
Tracing the Dynamical Mass in Galaxy Disks Using H I Velocity Dispersion and Its Implications for the Dark Matter Distribution in Galaxies. We present a method to derive the dynamical mass of face-on galaxy disks using their neutral hydrogen (H I) velocity dispersion (σH I). We have applied the method to nearby, gas-rich galaxies that have extended H I gas disks and have low inclinations. The galaxy sample includes four large disk galaxies, NGC 628, NGC 6496, NGC 3184, and NGC 4214, and three dwarf galaxies, DDO 46, DDO 63, and DDO 187. We have used archival H I data from The H I Nearby Galaxy Survey (THINGS) and the LITTLE THINGS survey to derive the H I gas distributions and Spitzer mid-infrared images to determine the stellar disk mass distributions. We examine the disk dynamical and baryonic mass ratios in the extreme outer disks where there is H I gas but no visible stellar disk. We find that for the large galaxies, the disk dynamical and H I gas mass surface densities are comparable in the outer disks. But in the smaller dwarf galaxies, for which the total H I gas mass dominates the baryonic mass, I.e., M(H I) ≥ M(stars), the disk dynamical mass is much larger than the baryonic mass. For these galaxies, there must either be a very low-luminosity stellar disk which provides the vertical support for the H I gas disk or there is halo dark matter associated with their disks, which is possible if the halo has an oblate shape so that the inner part of the dark matter halo is concentrated around the disk. Our results are important for explaining the equilibrium of H I disks in the absence of stellar disks and is especially important for gas-rich, dwarf galaxies that appear to have significant dark matter masses associated with their disks.

Keywords: Galaxy dark matter halos, Dark matter distribution, Galaxy stellar disks, Spiral galaxies, Dwarf galaxies, H I line emission, Galaxy disks
Electron Acceleration from Expanding Magnetic Vortices During Reconnection with a Guide Field. Magnetic reconnection is believed to be responsible for the acceleration of energetic electrons with a power-law spectrum in the solar wind and solar flares. However, recent studies of the leading mechanism of electron acceleration in reconnection, namely the acceleration by tearing instability induced multi-islands, demonstrates that this mechanism suffers from an "injection problem" for mildly relativistic reconnection acceleration. In this paper, we investigate a new type of reconnection acceleration in which an electron Kelvin-Helmholtz instability (EKHI) is driven as the current sheet reaches electron inertial length scales during magnetic reconnection with a strong guide field. Electrons are accelerated by stochastic electric fields, induced by the EKHI generated vortices that expand rapidly, and a power-law electron energy spectrum $f(W)\propto {W}^{-\alpha }$ with index α ∼ 3.5 is produced (W is the electron kinetic energy and f(W) is the energy distribution function). We show that the mechanism is a second-order Fermi acceleration process, and the index $\alpha =(1+4{a}^{2}D/R)/2$ where a = Bg/B0, which is determined by the ratio of the spatial scale of the inductive electric field D to that of vortices R and the ratio of guide field Bg to asymptotic magnetic field B0.

Keywords: Solar energetic particles, Solar flares, Solar magnetic reconnection
Discovery of a Spatially Extended GeV Source in the Vicinity of the TeV Halo Candidate 2HWC J1912+099: a TeV Halo or Supernova Remnant?. Observations by the High-Altitude Water Cherenkov Observatory (HAWC) and Milagro have detected spatially extended TeV sources surrounding middle-aged (t ∼ 100-400 kyr) pulsars like Geminga and PSR B0656+14, which have been named "TeV halos," representing very extended TeV pulsar wind nebulae (PWNe) powered by relatively old pulsars. A few more HAWC-detected sources have been suggested to be TeV halo candidates. In this paper, we search for possible GeV counterparts of three TeV halo candidates with Fermi Large Area Telescopes. We detect a new spatially extended GeV source in the vicinity of the TeV halo candidate 2HWC J1912+099, which is also detected by the High Energy Stereoscopic System (H.E.S.S.) (HESS J1912+101). We find that the size of the GeV source is significantly larger than that of the TeV emission measured by H.E.S.S., and a spatial template characteristic of a PWN can fit the GeV data. We suggest that the GeV source is an extended PWN powered by the central middle-aged pulsar PSR J1913+1011. This discovery favors the TeV halo scenario for the TeV source 2HWC J1912+099 (HESS J1912+101), although the possible shell-like morphology measured by H.E.S.S. challenges this interpretation. Alternatively, the TeV emission could be dominated by a supernova remnant via the hadronic process. Future multi-wavelength observations of the source and more precise measurements of the spatial profile of the TeV emission will be useful to distinguish between the two scenarios.

Keywords: Cosmic rays, High-energy cosmic radiation, Pulsars
Models of the Mass-ejection Histories of Pre-planetary Nebulae. IV. Magnetized Winds and the Origins of Jets, Bullets, and FLIERs. This paper explores the influences and consequences of toroidal magnetic fields in shaping the visible lobes of pre-planetary nebulae (prePNe). To probe these influences we start with the steady, diverging, and field-free wind model of our previous papers and add weak to moderate toroidal fields to the winds in order to generate arrays of outcomes after 500 yr, after which the structures grow almost homologously. As expected, toroidal fields in the stellar winds invariably form very thin and dense axial features whose structure is best described as a thin cold jet with an ultra-dense and neutral leading knot, or bullet, at its tip. The speed of the leading knot depends only on the density contrast (the ratio of injected to ambient gas densities at the nozzle) and wind injection speed, but not on the field strength or opening angle. The lobes formed by the ram pressure of the winds take a variety of forms and sizes that depend primarily on the geometric structure of the injected gas and the density contrast. About 20% of the Hubble Space Telescope images of prePNe show unique signatures of shaping by toroidal fields. Pairs of low-ionization knots seen along the major axis of fully ionized PNe, often called FLIERs, are easily explained as the very dense, cold, and neutral remnants of magnetically formed knots.

Keywords: Protoplanetary nebulae, Stellar winds, Jets, Post-asymptotic giant branch
The Activation of Galactic Nuclei and Their Accretion Rates Are Linked to the Star Formation Rates and Bulge-types of Their Host Galaxies. We use bulge-type classifications of 809 representative Sloan Digital Sky Survey galaxies by Gadotti to classify a large sample of galaxies into real bulges (classical or elliptical) and pseudobulges using Random Forest. We use structural and stellar population predictors that can easily be measured without image decomposition. Multiple parameters—such as the central-mass density with 1 kpc, concentration index, Sérsic index, and velocity dispersion—result in accurate bulge classifications when combined together. We classify ∼44,500 face-on galaxies above stellar mass of 1010 M⊙ and redshift 0.02 &lt; z &lt; 0.07 into real bulges or pseudobulges with 93% ± 2% accuracy. We show that ∼75%-90% of active galactic nuclei (AGNs) identified by the optical line ratio diagnostic are hosted by real bulges. The pseudobulge fraction significantly decreases with AGN signature as the line ratios change from indicating pure star formation (∼54% ± 4%), to composite of star formation and AGN (∼18% ± 3%), and to AGN-dominated galaxies (∼5% ± 3%). Using the dust-corrected [O III] luminosity as an AGN accretion indicator, and the stellar mass and radius as proxies for a black hole mass, we find that AGNs in real bulges have lower Eddington ratios than AGNs in pseudobulges. Real bulges have a wide range of AGN and star formation activities, although most of them are weak AGNs. For both bulge-types, their Eddington ratios are correlated with specific star formation rates (SSFR). Real bulges have a lower specific accretion rate but higher AGN fraction than pseudobulges do at similar SSFRs.

Keywords: Black holes, Galaxy bulges, Galaxy classification systems, Active galactic nuclei, Galaxy quenching, Random Forests
The Effects of Dust Optical Properties on the Scattering-induced Disk Polarization by Millimeter-sized Grains. Spatially resolved (sub)millimeter polarization has been detected by Atacama Large Millimeter/submillimeter Array in an increasing number of disks. The majority of the observations show polarization patterns consistent with self scattering, especially at Band 7. The inferred sizes of the grains are typically of order 100 μm, which is very different from the millimeter size commonly inferred from the dust opacity index β. In an effort to resolve this discrepancy, we first introduce the so-called "Coplanar Isotropic Radiation Field" approximation, which enables the computation of the (signed) polarization fraction semianalytically. With an oft-adopted dust composition, we find that models with big dust grains produce very small polarization with reversed orientation, which has not been observed. The semianalytic results are validated through Monte Carlo radiative transfer simulations. In these models, the "correct" polarization orientation and the small β index are mutually exclusive. To resolve this tension, we explore a wide range of dust models, parameterized by their complex refractive indices m = n + ik. We find that both the fraction and the orientation of the polarization depend on the refractive index in a complex way, and this dependence is mapped out on an n-k plane for a representative 3 mm size distribution and wavelength of 870 μm. In particular, 3 mm-sized refractory organics grains produce reversed polarization, whereas grains made of absorptive carbonaceous materials produce a percent-level, nonreversed polarization; the latter may alleviate the aforementioned tension in grain size estimates. We conclude that scattering-induced polarization has the potential to also probe the grain compositions.

Keywords: Circumstellar dust, Dust continuum emission, Protoplanetary disks
An Empirically Derived Formula for the Shape of Planet-induced Gaps in Protoplanetary Disks. This study uses numerical hydrodynamics calculations and a novel method for densely sampling parameter space to measure the precise shape of a gap opened by a planet in a gaseous disk, as a function of planet-to-star mass ratio, disk Mach number, and disk viscosity. Formulas for gap depth and width are determined, which are combined to form a complete formula for surface density as a function of radius in the disk. This new analytical formula is compared with numerically derived gaps opened by planets ranging from very low masses up to a few times Jupiter's mass, and excellent agreement is found over a wide range of parameter space relevant to planet-disk interactions. A simple-to-use code is presented to rapidly generate synthetic disk profiles.

Keywords: Hydrodynamical simulations, Hydrodynamics, Protoplanetary disks, Exoplanet formation, Astrophysical fluid dynamics, Planet formation
Accretion History of AGNs. II. Constraints on AGN Spectral Parameters Using the Cosmic X-Ray Background. We constrain X-ray spectral shapes for the ensemble of active galactic nuclei (AGNs) based on the shape of the cosmic X-ray background (CXB). Specifically, we rule out regions of X-ray spectral parameter space that do not reproduce the CXB in the energy range 1-100 keV. The key X-ray spectral parameters are the photon index, Γ; the cutoff energy, Ecutoff; and the reflection scaling factor, R. Assuming each parameter follows a Gaussian distribution, we first explore the parameter space using a Bayesian approach and a fixed X-ray luminosity function (XLF). For σE = 36 keV and σR = 0.14, fixed at the observed values from the Swift-BAT 70-month sample, we allow $\langle R\rangle ,\langle {E}_{\mathrm{cutoff}}\rangle $ and $\langle {\rm{\Gamma }}\rangle $ to vary subject to reproducing the CXB. We report results for σΓ = 0.1-0.5. In an alternative approach, we define the parameter distributions, then forward model to fit the CXB by perturbing the XLF using a neural network. This approach allows us to rule out parameter combinations that cannot reproduce the CXB for any XLF. The marginalized conditional probabilities for the four free parameters are: $\langle R\rangle \,={0.99}_{-0.26}^{+0.11},\langle {E}_{\mathrm{cutoff}}\rangle ={118}_{-23}^{+24},{\sigma }_{{\rm{\Gamma }}}={0.101}_{-0.001}^{+0.097}$ and $\langle {\rm{\Gamma }}\rangle ={1.9}_{-0.09}^{+0.08}$ . We provide an interactive online tool for users to explore any combination of $\langle {E}_{\mathrm{cutoff}}\rangle $ , σE, $\langle {\rm{\Gamma }}\rangle $ , σΓ, $\langle R\rangle $ , and σR, including different distributions for each absorption bin, subject to the integral CXB constraint. The distributions observed in many AGN samples can be ruled out by our analysis, meaning these samples cannot be representative of the full AGN population. The few samples that fall within the acceptable parameter space are hard-X-ray-selected, commensurate with their having fewer selection biases.

Keywords: Supermassive black holes, Quasars, Active galactic nuclei, X-ray active galactic nuclei, X-ray surveys, X-ray sources, Diffuse x-ray background, Astrophysical black holes
Three-component Kinematics of Multiple Stellar Populations in Globular Clusters with Gaia and VLT. The internal dynamics of multiple stellar populations in globular clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and velocity dispersion, could be related to the initial configuration of the system. In recent work, we provided the first study of the kinematics of different stellar populations in NGC 0104 over a large field of view in the plane of the sky, exploiting Gaia Data Release 2 (DR2) proper motions combined with multi-band ground-based photometry. In this paper, we combine Gaia DR2 proper motions with Very Large Telescope radial velocities to investigate the kinematics along the line of sight and in the plane of the sky of multiple populations in seven GCs, namely NGC 0104, NGC 0288, NGC 5904, NGC 6121, NGC 6254, NGC 6752, and NGC 6838. Among the analyzed clusters, only NGC 0104 and NGC 5904 show significant rotation. Separating our sample into two groups of first- and second-population stars (1P and 2P) we find that overall these two populations exhibit a similar rotation pattern in NGC 0104. However, some hints of different rotation are observed in the external regions of this cluster. Interestingly, 1P and 2P stars in NGC 5904 show different rotation curves, with distinct phases and such differences are significant at the ∼2.5σ level. The analysis of the velocity-dispersion profiles of multiple populations confirms that 2P stars of NGC 0104 show stronger anisotropy than the 1P.

Keywords: Globular star clusters, Stellar populations, Proper motions, Stellar kinematics
As a Matter of State: The Role of Thermodynamics in Magnetohydrodynamic Turbulence. Turbulence simulations play a key role in advancing the general understanding of the physical properties of turbulence and in interpreting astrophysical observations of turbulent plasmas. For the sake of simplicity, however, turbulence simulations are often conducted in the isothermal limit. Given that the majority of astrophysical systems are not governed by isothermal dynamics, we aim to quantify the impact of thermodynamics on the physics of turbulence, through varying adiabatic index, γ, combined with a range of optically thin cooling functions. In this paper, we present a suite of ideal magnetohydrodynamics simulations of thermally balanced stationary turbulence in the subsonic, super-Alfvénic, high ${\beta }_{{\rm{p}}}$ (ratio of thermal to magnetic pressure) regime, where turbulent dissipation is balanced by two idealized cooling functions (approximating linear cooling and free-free emission) and examine the impact of the equation of state by considering cases that correspond to isothermal, monatomic, and diatomic gases. We find a strong anticorrelation between thermal and magnetic pressure independent of thermodynamics, whereas the strong anticorrelation between density and magnetic field found in the isothermal case weakens with increasing γ. Similarly, the linear relation between variations in density and thermal pressure with sonic Mach number becomes steeper with increasing γ. This suggests that there exists a degeneracy in these relations with respect to thermodynamics and Mach number in this regime, which is dominated by slow magnetosonic modes. These results have implications for attempts to infer (e.g.,) Mach numbers from (e.g.,) Faraday rotation measurements, without additional information regarding the thermodynamics of the plasma. However, our results suggest that this degeneracy can be broken by utilizing higher-order moments of observable distribution functions.

Keywords: Magnetohydrodynamics, Plasma astrophysics, Intracluster medium, Astrophysical fluid dynamics, Magnetohydrodynamical simulations
The Circumstellar Environment around the Embedded Protostar EC 53. EC 53 is an embedded protostar with quasi-periodic emission in the near-IR and submillimeter. We use Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution observations of continuum and molecular line emission to describe the circumstellar environment of EC 53. The continuum image reveals a disk with a flux that suggests a mass of 0.075 M⊙, much less than the estimated mass in the envelope, and an in-band spectral index that indicates grain growth to centimeter sizes. Molecular lines trace the outflow cavity walls, infalling and rotating envelope, and/or the Keplerian disk. The rotation profile of the C17O 3-2 line emission cannot isolate the Keplerian motion clearly, although the lower limit of the protostellar mass can be calculated as 0.3 ± 0.1 M⊙ if the Keplerian motion is adopted. The weak CH3OH emission, which is anticorrelated with the H13CO+ 4-3 line emission, indicates that the water snow line is more extended than what expected from the current luminosity, attesting to bygone outburst events. The extended snow line may persist for longer at the disk surface because the lower density increases the freeze-out timescale of methanol and water.

Keywords: Interstellar molecules, Protostars, Spectral index, Protoplanetary disks
Characterizing Magnetic Reconnection Regions Using Gaussian Mixture Models on Particle Velocity Distributions. We present a method based on unsupervised machine learning to identify and characterize regions of interest using particle velocity distributions as a signature pattern. An automatic density estimation technique is applied to particle distributions provided by particle-in-cell simulations to study magnetic reconnection regions. Its application to magnetic reconnection is new. The key components of the method involve (I) a Gaussian mixture model determining the presence of a given number of subpopulations within an overall population, and (II) a model selection technique with a Bayesian information criterion to estimate the appropriate number of subpopulations. Thus, this method automatically identifies the presence of complex distributions, such as beams or other non-Maxwellian features, and can be used as a detection algorithm able to identify reconnection regions. The approach is demonstrated for a specific double Harris sheet simulation, but it can in principle be applied to any other type of simulation data on the particle distribution function.

Keywords: Gaussian mixture model, Plasma astrophysics, Solar magnetic reconnection