Sazuna/UAT_keywords huggingface dataset:
Radial Evolution of Thermal and Suprathermal Electron Populations in the Slow Solar Wind from 0.13 to 0.5 au: Parker Solar Probe Observations. We develop and apply a bespoke fitting routine to a large volume of solar wind electron distribution data measured by Parker Solar Probe over its first five orbits, covering radial distances from 0.13 to 0.5 au. We characterize the radial evolution of the electron core, halo, and strahl populations in the slow solar wind during these orbits. The fractional densities of these three electron populations provide evidence for the growth of the combined suprathermal halo and strahl populations from 0.13 to 0.17 au. Moreover, the growth in the halo population is not matched by a decrease in the strahl population at these distances, as has been reported for previous observations at distances greater than 0.3 au. We also find that the halo is negligible at small heliocentric distances. The fractional strahl density remains relatively constant at ~1% below 0.2 au, suggesting that the rise in the relative halo density is not solely due to the transfer of strahl electrons into the halo.

Keywords: The Sun, Solar wind, Heliosphere, Plasma physics
Multiple Measurements of Gravitational Waves Acting as Standard Probes: Model-independent Constraints on the Cosmic Curvature with DECIGO. Although the spatial curvature has been precisely determined via observations of the cosmic microwave background by the Planck satellite, it still suffers from the well-known cosmic curvature tension. As a standard siren, gravitational waves (GWs) from binary neutron star mergers provide a direct way to measure the luminosity distance. In addition, the accelerating expansion of the universe may cause an additional phase shift in the gravitational waveform, which will allow us to measure the acceleration parameter. This measurement provides an important opportunity to determine the curvature parameter Ω k  in the GW domain based on the combination of two different observables for the same objects at high redshifts. In this study, we investigate how such an idea could be implemented with the future generation of the space-based Decihertz Interferometer Gravitational-wave Observatory (DECIGO) in the framework of two model-independent methods. Our results show that DECIGO could provide a reliable and stringent constraint on the cosmic curvature at a precision of ΔΩ k  = 0.12, which is comparable to existing results based on different electromagnetic data. Our constraints are more stringent than the traditional electromagnetic method from the Pantheon sample of Type Ia supernovae, which shows no evidence for a deviation from a flat universe at z ~ 2.3. More importantly, with our model-independent method, such a second-generation space-based GW detector would also be able to explore the possible evolution of Ω k  with redshift, through direct measurements of cosmic curvature at different redshifts (z ~ 5). Such a model-independent Ω k  reconstruction to the distant past could become a milestone in gravitational-wave cosmology.

Keywords: Gravitational waves, Cosmological parameters
The Next Generation Virgo Cluster Survey. XXXIII. Stellar Population Gradients in the Virgo Cluster Core Globular Cluster System. We present a study of the stellar populations of globular clusters (GCs) in the Virgo Cluster core with a homogeneous spectroscopic catalog of 692 GCs within a major-axis distance R maj = 840 kpc from M87. We investigate radial and azimuthal variations in the mean age, total metallicity, [Fe/H], and α-element abundance of blue (metal-poor) and red (metal-rich) GCs using their co-added spectra. We find that the blue GCs have a steep radial gradient in [Z/H] within R maj = 165 kpc, with roughly equal contributions from [Fe/H] and [α/Fe], and flat gradients beyond. By contrast, the red GCs show a much shallower gradient in [Z/H], which is entirely driven by [Fe/H]. We use GC-tagged Illustris simulations to demonstrate an accretion scenario where more massive satellites (with more metal- and α-rich GCs) sink further into the central galaxy than less massive ones, and where the gradient flattening occurs because of the low GC occupation fraction of low-mass dwarfs disrupted at larger distances. The dense environment around M87 may also cause the steep [α/Fe] gradient of the blue GCs, mirroring what is seen in the dwarf galaxy population. The progenitors of red GCs have a narrower mass range than those of blue GCs, which makes their gradients shallower. We also explore spatial inhomogeneity in GC abundances, finding that the red GCs to the northwest of M87 are slightly more metal-rich. Future observations of GC stellar population gradients will be useful diagnostics of halo merger histories.

Keywords: Globular star clusters, Galaxy clusters, Virgo Cluster, Stellar populations, Chemical abundances, Giant elliptical galaxies
The CO Emission in the Taffy Galaxies (UGC 12914/15) at 60 pc Resolution. I. The Battle for Star Formation in the Turbulent Taffy Bridge. We present Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of 0.″2 (60 pc) of CO emission from the Taffy galaxies (UGC 12914/5). The observations are compared with narrowband Paα, mid-IR, radio continuum and X-ray imaging, plus optical spectroscopy. The galaxies have undergone a recent head-on collision, creating a massive gaseous bridge that is known to be highly turbulent. The bridge contains a complex web of narrow molecular filaments and clumps. The majority of the filaments are devoid of star formation, and fall significantly below the Kennicutt-Schmidt relationship for normal galaxies, especially for the numerous regions undetected in Paα emission. Within the loosely connected filaments and clumps of gas we find regions of high velocity dispersion that appear gravitationally unbound for a wide range of likely values of X CO. Like the "Firecracker" region in the Antennae system, they would require extremely high external dynamical or thermal pressure to stop them dissipating rapidly on short crossing timescales of 2-5 Myr. We suggest that the clouds may be transient structures within a highly turbulent multiphase medium that is strongly suppressing star formation. Despite the overall turbulence in the system, stars seem to have formed in compact hotspots within a kiloparsec-sized extragalactic H II region, where the molecular gas has a lower velocity dispersion than elsewhere, and shows evidence for a collision with an ionized gas cloud. Like the shocked gas in the Stephan's Quintet group, the conditions in the Taffy bridge shows how difficult it is to form stars within a turbulent, multiphase, gas.

Keywords: Interacting galaxies
Electrostatic Lofting Conditions for Supercharged Dust. Electrostatic dust lofting may be a common occurrence on small bodies in the solar system, whereby the upward electrostatic force on a grain is able to overcome the surface gravity and cohesion binding it to the surface. This electrostatic lofting may serve to redistribute and transport dust across the surface of these bodies to produce features such as dust ponds and lineations found on Eros, or even to rid bodies of small particles completely. Classical models, which distribute charge evenly across a dust grain, have historically predicted electric field strengths that are insufficient to loft dust. However, recent studies have developed grain-scale charging models that account for the buildup of charge in the microcavities of regolith and assume unequal distribution of charge on a dust grain. These models predict electric field strengths orders of magnitude larger than classical models, which may explain how electrostatic dust lofting occurs on small bodies. In this paper, we compare the grain-scale supercharging models developed by Zimmerman et al. and survey how the different parameters affect grain charging-namely, charge separation, grain size, and dielectric breakdown strength. Furthermore, we investigate how each of the charging models can be used to bound initial condition requirements such as charge and velocity for dust lofting to occur on these small bodies. Initial condition requirements are examined for a range of grain sizes, regolith cohesive strengths, and small body sizes.

Keywords: Surface processes, Planetary surfaces, Asteroids, Asteroid surfaces
Neutrino Rocket Jet Model: An Explanation of High-velocity Pulsars and Their Spin-down Evolution. The fact that the spatial velocity of pulsars is generally higher than that of their progenitor stars has bothered astronomers for nearly 50 years. It has been extensively argued that the high pulsar velocity should be acquired during a natal kick process on a timescale of 100 ms-10 s in the supernova explosion, in which some asymmetrical dynamical mechanism plays a key role. However, a satisfactory picture generally is still lacking. In this study, it is argued that the neutrino rocket model can well account for the high speed as well as the long-term evolution behaviors of pulsars. The neutrinos are emitted from superfluid vortex neutrons through the neutrino cyclotron radiation mechanism. The unique characters of left-handed neutrinos and right-handed antineutrinos resulting from the nonconservation of parity in weak interactions play a major role in the spatial asymmetry. The continuous acceleration of pulsars can be naturally explained by this model, which yields a maximum velocity surpassing 1000 km s-1. The alignment between the spinning axis and the direction of motion observed for the Crab pulsar (PSR 0531) and the Vela pulsar (PSR 0833) can be well accounted for. The observed correlation between the spin-down rate and the period of long-period pulsars with P ≳ 0.5 s can also be satisfactorily explained.

Keywords: Neutron stars, Stellar evolutionary models, Proper motions, Pulsars
Not That Simple: The Metallicity Dependence of the Wide Binary Fraction Changes with Separation and Stellar Mass. The metallicity dependence of the wide binary fraction (WBF) is critical for studying the formation of wide binaries. While controversial results have been found in recent years, here we combine the wide binary catalog recognized from Gaia EDR3 and stellar parameters from LAMOST to investigate this topic. Taking the bias of the stellar temperature at given separations into account, we find that the relationship between the WBF and metallicity depends on the temperature for the thin disk at s &gt; 200 au. It changes from negative to positive as the temperature increases from 4000 to 7500 K. This temperature/mass dependence is not seen for the thick disk. Besides, the general tendency between the WBF and metallicity varies with the separation, consistent with previous results. It shows anticorrelation at small separations, s &lt; 200 au for the thin disk and s &lt; 600 au for the thick disk. Then it becomes an "arcuate" shape at larger separations (hundreds to thousands of astronomical units), peaking at [Fe/H] ≈0.1 for the thin disk and [Fe/H] ≈-0.5 for the thick disk. Finally it becomes roughly flat for the thin disk at 1000 &lt; s &lt; 10,000 au. Our work provides new observational evidence for theoretical studies on binary formation and evolution.

Keywords: Wide binary stars, Stellar abundances, Stellar physics
Constraints on Cosmic Rays in the Milky Way Circumgalactic Medium from O VIII Observations. We constrain the cosmic-ray (CR) population in the circumgalactic medium (CGM) of the Milky Way by comparing the observations of absorption lines of O VIII ions with predictions from analytical models of the CGM: the precipitation (PP) and isothermal (IT) models. For a CGM in hydrostatic equilibrium, the introduction of CR suppresses thermal pressure and affects the O VIII ion abundance. We explore the allowances given to the ratio of CR pressure to thermal pressure (P CR/P th = η), with varying boundary conditions, CGM mass content, photoionization by extragalactic ultraviolet background, and temperature fluctuations. We find that the allowed maximum values of η are η ≲ 10 in the PP model and η ≲ 6 in the IT model. We also explore the spatial variation of η: rising (η = Ax) or declining (η = A/x) with radius, where A is the normalization of the profiles. In particular, the models with a declining ratio of CR to thermal pressure fare better than those with a rising ratio with suitable temperature fluctuation (higher σ lnT for PP and lower for IT). The declining profiles allow A ≲ 8 and A ≲ 10 in the case of the IT and PP models, respectively, thereby accommodating a large value of η (≃200) in the central region but not in the outer regions. These limits, combined with the limits derived from the γ-ray and radio background, can be useful for building models of the Milky Way CGM including the CR population. However, the larger amount of CRs can be packed in the cold phase, which may be one way to circumvent these constraints.

Keywords: Circumgalactic medium, Cosmic rays
Scattering of Lyα Photons through the Reionizing Intergalactic Medium: I. Spectral Energy Distribution. During reionization, a fraction of galactic Lyα emission is scattered in the intergalactic medium (IGM) and appears as diffuse light extending megaparsecs from the source. We investigate how to probe the properties of the early galaxies and their surrounding IGM using this scattered light. We create a Monte Carlo algorithm to track individual photons and reproduce several test cases from previous literature. Then, we run our code on the simulated IGM of the CoDaII simulation. We find that the scattered light can leave an observable imprint on the emergent spectrum if collected over several square arcminutes. Scattering can redden the emission by increasing the path lengths of photons, but it can also make the photons bluer by upscattering them according to the peculiar motion of the scatterer. The photons emitted on the far blue side of the resonance appear more extended in both frequency and space compared to those emitted near the resonance. This provides a discriminating feature for the blueward emission, which cannot be constrained from the unscattered light coming directly from the source. The ionization state of the IGM also affects the scattered light spectrum. When the source is in a small H II region, the emission goes through more scatterings in the surrounding H I region regardless of the initial frequency and ends up more redshifted and spatially extended. This can result in a weakening of the scattered light toward high z during reionization. Our results provide a framework for interpreting the scattered light to be measured by high-z integral-field-unit surveys.

Keywords: Early universe, Reionization, Observational cosmology, Intergalactic medium
MARS: A New Maximum-entropy-regularized Strong Lensing Mass Reconstruction Method. Free-form strong-lensing (SL) mass reconstructions typically suffer from overfitting, which manifests itself as false-positive small-scale fluctuations. We present a new free-form MAximum-entropy ReconStruction (MARS) method without the assumption that light traces mass (LTM). The MARS algorithm enables us to achieve excellent convergence in source positions (~0.″001), minimize spurious small-scale fluctuations, and provide a quasi-unique solution independently of initial conditions. Our method is tested with the publicly available synthetic SL data FF-SIMS. The comparison with the truth shows that the mass reconstruction quality is on par with those of the best-performing LTM methods published in the literature, which have been demonstrated to outperform existing free-form methods. In terms of the radial mass profile reconstruction, we achieve &lt;1% agreement with the truth for the regions constrained by multiple images. Finally, we apply MARS to A1689 and find that the cluster mass in the SL regime is dominated by the primary halo centered on the brightest cluster galaxy and the weaker secondary halo is also coincident with the bright cluster member ~160 kpc northeast. Within the SL field, the A1689 radial profile is well described by a Navarro-Frenk-White profile with c 200 = 5.53 ± 0.77 and ${r}_{s}={538}_{-100}^{+90}$ kpc, and we find no evidence that A1689 is overconcentrated.

Keywords: Galaxy clusters, Dark matter distribution, Strong gravitational lensing
GeV Gamma-Ray Emission and Molecular Clouds toward Supernova Remnant G35.6-0.4 and the TeV Source HESS J1858+020. It is difficult to distinguish the hadronic process from the leptonic one in γ-ray observation, which is however crucial in revealing the origin of cosmic rays. As an endeavor in this regard, we focus in this work on the complex γ-ray emitting region, which partially overlaps with the unidentified TeV source HESS J1858+020 and includes supernova remnant (SNR) G35.6-0.4 and H II region G35.6-0.5. We reanalyze CO line, H I, and Fermi-LAT GeV γ-ray emission data of this region. The analysis of the molecular and H I data suggests that SNR G35.6-0.4 and H II region G35.6-0.5 are located at different distances. The analysis of the GeV γ-rays shows that GeV emission arises from two point sources: one (SrcA) coincident with the SNR, and the other (SrcB) coincident with both HESS J1858+020 and H II region G35.6-0.5. The GeV emission of SrcA can be explained by the hadronic process in the SNR-molecular cloud association scenario. The GeV-band spectrum of SrcB and the TeV-band spectrum of HESS J1858+020 can be smoothly connected by a power-law function, with an index of ~2.2. The connected spectrum is well explained with a hadronic emission, with the cutoff energy of protons above 1 PeV. It thus indicates that there is a potential PeVatron in the H II region and should be further verified with ultrahigh-energy observations with, e.g., LHAASO.

Keywords: Supernova remnants, Gamma-ray sources, Gamma-rays, Molecular clouds
Preacceleration in the Electron Foreshock. I. Electron Acoustic Waves. To undergo diffusive shock acceleration, electrons need to be preaccelerated to increase their energies by several orders of magnitude, else their gyroradii will be smaller than the finite width of the shock. In oblique shocks, where the upstream magnetic field orientation is neither parallel nor perpendicular to the shock normal, electrons can escape to the shock upstream, modifying the shock foot to a region called the electron foreshock. To determine the preacceleration in this region, we undertake particle-in-cell simulations of oblique shocks while varying the obliquity and in-plane angles. We show that while the proportion of reflected electrons is negligible for θ Bn = 74.°3, it increases to R ~ 5% for θ Bn = 30°, and that, via the electron acoustic instability, these electrons power electrostatic waves upstream with energy density proportional to R 0.6 and a wavelength ≈2λ se, where λ se is the electron skin length. While the initial reflection mechanism is typically a combination of shock-surfing acceleration and magnetic mirroring, we show that once the electrostatic waves have been generated upstream, they themselves can increase the momenta of upstream electrons parallel to the magnetic field. In ≲1% of cases, upstream electrons are prematurely turned away from the shock and never injected downstream. In contrast, a similar fraction is rescattered back toward the shock after reflection, reinteracts with the shock with energies much greater than thermal, and crosses into the downstream.

Keywords: Shocks
ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar Evolution. Protostellar outflows and jets play a vital role in star formation as they carry away excess angular momentum from the inner disk surface, allowing the material to be transferred toward the central protostar. Theoretically, low-velocity and poorly collimated outflows appear from the beginning of the collapse at the first hydrostatic core (FHSC) stage. With growing protostellar core mass, high-density jets are launched, entraining an outflow from the infalling envelope. Until now, molecular jets have been observed at high velocity (≳100 km s-1) in early Class 0 protostars. We, for the first time, detect a dense molecular jet in SiO emission with low velocity (~4.2 km s-1, deprojected ~24 km s-1) from source G208.89-20.04Walma (hereafter G208Walma) using ALMA Band 6 observations. This object has some characteristics of FHSCs, such as a small outflow/jet velocity, extended 1.3 mm continuum emission, and N 2D+ line emission. Additional characteristics, however, are typical of early protostars: collimated outflow and SiO jet. The full extent of the outflow corresponds to a dynamical timescale of ~ ${930}_{-100}^{+200}$ yr. The spectral energy distribution also suggests a very young source having an upper limit of T bol ~ 31 K and L bol ~ 0.8 L ⊙. We conclude that G208Walma is likely in the transition phase from FHSC to protostar, and the molecular jet has been launched within a few hundred years of initial collapse. Therefore, G208Walma may be the earliest object discovered in the protostellar phase with a molecular jet.

Keywords: Early stellar evolution, Stellar jets, Astrochemistry, Stellar mass loss, Stellar winds, Young stellar objects, Star formation, Low mass stars, Protostars, Stellar evolution
Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves. II. Period-Fourier-Metallicity Relations for First Overtone RR Lyrae. We present new period-ϕ 31-[Fe/H] relations for first-overtone RRL stars (RRc), calibrated over a broad range of metallicities (-2.5 ≲ [Fe/H] ≲ 0.0) using the largest currently available set of Galactic halo field RRL with homogeneous spectroscopic metallicities. Our relations are defined in the optical (ASAS-SN V band) and, inaugurally, in the infrared (WISE W1 and W2 bands). Our V-band relation can reproduce individual RRc spectroscopic metallicities with a dispersion of 0.30 dex over the entire metallicity range of our calibrator sample (an rms smaller than what we found for other relations in literature including nonlinear terms). Our infrared relation has a similar dispersion in the low- and intermediate-metallicity range ([Fe/H] ≲ -0.5), but tends to underestimate the [Fe/H] abundance around solar metallicity. We tested our relations by measuring both the metallicity of the Sculptor dSph and a sample of Galactic globular clusters, rich in both RRc and RRab stars. The average metallicity we obtain for the combined RRL sample in each cluster is within ±0.08 dex of their spectroscopic metallicities. The infrared and optical relations presented in this work will enable deriving reliable photometric RRL metallicities in conditions where spectroscopic measurements are not feasible; e.g., in distant galaxies or reddened regions (observed with upcoming Extremely Large Telescopes and the James Webb Space Telescope), or in the large sample of new RRL that will be discovered in large-area time-domain photometric surveys (such as the LSST and the Roman space telescope).

Keywords: Globular star clusters, Pulsating variable stars, RRc variable stars, RR Lyrae variable stars, Metallicity