Sazuna/UAT_keywords huggingface dataset:
A Physically Motivated Framework to Compare the Merger Timescales of Isolated Low- and High-mass Galaxy Pairs Across Cosmic Time. The merger timescales of isolated low-mass pairs (108 &lt; M * &lt; 5 × 109 M ⊙) on cosmologically motivated orbits have not yet been studied in detail, though isolated high-mass pairs (5 × 109 &lt; M * &lt; 1011 M ⊙) have been studied extensively. It is common to apply the same separation criteria and expected merger timescales of high-mass pairs to low-mass systems, however, it is unclear if their merger timescales are similar, or if they evolve similarly with redshift. We use the Illustris TNG100 simulation to quantify the merger timescales of isolated low-mass and high-mass major pairs as a function of cosmic time, and explore how different selection criteria impact the mass and redshift dependence of merger timescales. In particular, we present a physically motivated framework for selecting pairs via a scaled separation criterion, wherein pair separations are scaled by the virial radius of the primary's Friends-of-Friends (FoF) group halo (r sep &lt; 1 R vir). Applying these scaled separation criteria yields equivalent merger timescales for both mass scales at all redshifts. Alternatively, static physical separation selections applied equivalently to all galaxy pairs at all redshifts lead to a difference in merger rate of up to ∼1 Gyr between low- and high-mass pairs, particularly for r sep &lt; 150 kpc. As a result, applying the same merger timescales to physical-separation-selected pairs will lead to a bias that systematically overpredicts low-mass galaxy merger rates.

Keywords: Galaxy interactions, Galaxy pairs, Galaxy dynamics, Galaxy mergers, Galaxy evolution, Field galaxies, Galaxies
Regulation of Solar Wind Electron Temperature Anisotropy by Collisions and Instabilities. Typical solar wind electrons are modeled as being composed of a dense but less energetic thermal "core" population plus a tenuous but energetic "halo" population with varying degrees of temperature anisotropies for both species. In this paper, we seek a fundamental explanation of how these solar wind core and halo electron temperature anisotropies are regulated by combined effects of collisions and instability excitations. The observed solar wind core/halo electron data in (β ∥, T ⊥/T ∥) phase space show that their respective occurrence distributions are confined within an area enclosed by outer boundaries. Here, T ⊥/T ∥ is the ratio of perpendicular and parallel temperatures and β ∥ is the ratio of parallel thermal energy to background magnetic field energy. While it is known that the boundary on the high-β ∥ side is constrained by the temperature anisotropy-driven plasma instability threshold conditions, the low-β ∥ boundary remains largely unexplained. The present paper provides a baseline explanation for the low-β ∥ boundary based upon the collisional relaxation process. By combining the instability and collisional dynamics it is shown that the observed distribution of the solar wind electrons in the (β ∥, T ⊥/T ∥) phase space is adequately explained, both for the "core" and "halo" components.

Keywords: Solar physics, Solar wind, Interplanetary physics, Heliosphere
The State of Solar Wind Heavy Ions in Interplanetary Coronal Mass Ejection–Driven Geomagnetic Storms. During geomagnetic storms, which are the primary periods for heavy ions from the solar wind to enter Earth's magnetospheric space, the charge state of solar wind heavy ions during these storms has significant implications for studying the distribution and effects of heavy ions in the magnetosphere. We analyzed the states and variations of heavy ions during 158 interplanetary coronal mass ejection (ICME)–driven geomagnetic storm events using data from the Advanced Composition Explorer satellite and examined four of these events in detail. We found that the increase in the average charge state of heavy ions such as O, Mg, Si, and Fe is positively correlated with the intensity of the geomagnetic storm. Regarding the abundance ratio of heavy ions such as Ne, Mg, Si, and Fe relative to oxygen ions, the rate and magnitude of increase in abundance ratios during extreme geomagnetic storms (Kp = 9) triggered by ICME events are significantly higher than those during other levels of geomagnetic storms. Additionally, we observed that although the average charge states of heavy ions such as O and Fe are correlated with the geomagnetic storm intensity induced by ICMEs, there are significant individual differences in the charge state variations of heavy ions.

Keywords: Geomagnetic fields, Solar wind, Solar coronal mass ejections, Charge exchange ionization
Unveiling the Connection between the Alfvénic Oval and the Open–Closed Field Line Boundary at Ganymede. Alfvén waves generated by the interactions between the Ganymede magnetosphere and the fast-corotating Jovian plasma carry a significant amount of energy. This energy is partially transferred to precipitating particles, which correspond to a feature called the Alfvénic oval. However, the spatial distribution of the Alfvénic oval in the Ganymede system is unclear, and the physical correlation between the Alfvénic oval and the open–closed field line boundary (OCFB) has not been studied quantitatively. Using a high-resolution, three-dimensional global magnetohydrodynamics simulation of Ganymede's magnetosphere, we investigate the spatial distribution of the Alfvénic oval mapped on the ionosphere surface of Ganymede based on upstream measurements from Juno's PJ34 flyby. Our results show that (1) the simulated Alfvénic oval of Ganymede closely resembles the observed aurora oval, and although without kinetic physics, the magnitude of the simulated Afvénic Poynting flux is significantly lower than the estimation based on auroral luminosity; (2) the OCFB aligns closely with the poleward (equatorial) boundary of the enhanced Alfvénic power on the downstream (upstream) side; and (3) the magnetospheric flux tube convection pattern can guide the Alfvénic wave packet to propagate toward latitudes either equatorward or poleward of the OCFB on the downstream/upstream side. These results, presented for the first time in this study, provide testable predictions for both the ongoing Juno mission and future Jovian missions such as JUICE probing the minimagnetosphere system.

Keywords: Magnetohydrodynamical simulations, Alfven waves, Ganymede, Aurorae
SDSS J0018-0939: A Clear Signature of Sub-Chandrasekhar Mass Type 1a Supernova. Very metal-poor (VMP) stars ([Fe/H] ≤ ‑2) that have subsolar values of [X/Fe] for α elements such as Mg, Si, and Ca, are referred to as α-poor VMP stars. They are quite rare among VMP stars and are thought to have formed from gas enriched predominantly by a single Type Ia supernova (SN 1a) in contrast to most VMP stars, which are α-enhanced and usually associated with core-collapse supernovae. The observed abundance pattern in such stars can provide a direct way to probe the nucleosynthesis in individual SN 1a. Although the abundance patterns in some α-poor VMP stars have been shown to be consistent with SN 1a ejecta, a clear nucleosynthetic signature for SN 1a resulting from the explosion of a near Chandrasekhar mass (near-M Ch) or a sub-Chandrasekhar mass (sub-M Ch) white dwarf, has not been unambiguously detected. We perform a detailed analysis of various formation channels of VMP stars and find that the α-poor VMP star SDSS J0018-0939, which was earlier reported as a star with potential pair-instability supernova origin, provides a near-smoking-gun signature of a sub-M Ch SN 1a resulting from He detonation. We find that compared to other α-poor VMP stars that were previously identified with SN 1a, SDSS J0018-0939 is the only star that has a clear and unambiguous signature of SN 1a. Interestingly, our results are consistent with constraints on SN1 a from recent galactic chemical evolution studies that indicate that sub-M Ch SN 1a accounts for ∼50%–75% of all SN 1a and is possibly the dominant channel in the early Galaxy.

Keywords: Population III stars, Population II stars, Type Ia supernovae, Stellar nucleosynthesis, Chemically peculiar stars
Magnetic Fields in a Sample of Planet-hosting M Dwarf Stars from Kepler, K2, and TESS Observed by APOGEE. Stellar magnetic fields have a major impact on space weather around exoplanets orbiting low-mass stars. From an analysis of Zeeman-broadened Fe I lines measured in near-infrared SDSS/APOGEE spectra, mean magnetic fields are determined for a sample of 29 M dwarf stars that host closely orbiting small exoplanets. The calculations employed the radiative transfer code Synmast and MARCS stellar model atmospheres. The sample M dwarfs are found to have measurable mean magnetic fields ranging between ∼0.2 and ∼1.5 kG, falling in the unsaturated regime on the versus P rot plane. The sample systems contain 43 exoplanets, which include 23 from Kepler, nine from K2, and nine from Transiting Exoplanet Survey Satellite. We evaluated their equilibrium temperatures, insolation, and stellar habitable zones and found that only Kepler-186f and TOI-700d are inside the habitable zones of their stars. Using the derived values of for the stars Kepler-186 and TOI-700 we evaluated the minimum planetary magnetic field that would be necessary to shield the exoplanets Kepler-186f and TOI-700d from their host star's winds, considering reference magnetospheres with sizes equal to those of the present-day and young Earth, respectively. Assuming a ratio of 5% between large- to small-scale B-fields, and a young-Earth magnetosphere, Kepler-186f and TOI-700d would need minimum planetary magnetic fields of, respectively, 0.05 and 0.24 G. These values are considerably smaller than Earth's magnetic field of 0.25 G ≲ B ≲ 0.65 G, which suggests that these two exoplanets might have magnetic fields sufficiently strong to protect their atmospheres and surfaces from stellar magnetic fields.

Keywords: M dwarf stars, Stellar magnetic fields, Stellar activity, Near infrared astronomy
Full Stokes-vector Inversion of the Solar Mg II h and k Lines. The polarization of the Mg II h and k resonance lines is the result of the joint action of scattering processes and the magnetic field–induced Hanle, Zeeman, and magneto-optical effects, thus holding significant potential for the diagnostic of the magnetic field in the solar chromosphere. The Chromospheric LAyer Spectro-Polarimeter sounding-rocket experiment, carried out in 2019, successfully measured at each position along the 196″ spectrograph slit the wavelength variation of the four Stokes parameters in the spectral region of this doublet around 280 nm, both in an active-region plage and in a quiet region close to the limb. We consider some of these CLASP2 Stokes profiles and apply to them the recently developed HanleRT Tenerife Inversion Code, which assumes a one-dimensional model atmosphere for each spatial pixel under consideration (i.e., it neglects the effects of horizontal radiative transfer). We find that the nonmagnetic causes of symmetry breaking, due to the horizontal inhomogeneities and the gradients of the horizontal components of the macroscopic velocity in the solar atmosphere, have a significant impact on the linear polarization profiles. By introducing such nonmagnetic causes of symmetry breaking as parameters in our inversion code, we can successfully fit the Stokes profiles and provide an estimation of the magnetic field vector. For example, in the quiet region pixels, where no circular polarization signal is detected, we find that the magnetic field strength in the upper chromosphere varies between 1 and 20 G.

Keywords: Spectropolarimetry, Atomic spectroscopy, Solar magnetic fields, Radiative transfer, Solar chromosphere
Coordinated JWST Imaging of Three Distance Indicators in a Supernova Host Galaxy and an Estimate of the Tip of the Red Giant Branch Color Dependence. Boasting a 6.5 m mirror in space, JWST can increase by several times the number of supernovae (SNe) to which a redshift-independent distance has been measured with a precision distance indicator (e.g., tip of the red giant branch (TRGB) or Cepheids); the limited number of such SN calibrators currently dominates the uncertainty budget in distance ladder Hubble constant (H 0) experiments. JWST/NIRCAM imaging of the Virgo Cluster galaxy NGC 4536 is used here to preview JWST program GO-1995, which aims to measure H 0 using three stellar distance indicators (Cepheids, TRGB, and J-branch asymptotic giant branch/carbon stars). Each population of distance indicator was here successfully detected—with sufficiently large number statistics, well-measured fluxes, and characteristic distributions consistent with ingoing expectations—so as to confirm that we can acquire distances from each method precise to about 0.05 mag (statistical uncertainty only). We leverage overlapping Hubble Space Telescope imaging to identify TRGB stars, crossmatch them with the JWST photometry, and present a preliminary constraint on the slope of the TRGB's F115W versus (F115W – F444W) relation equal to ‑0.99 ± 0.16 mag mag‑1. This slope is consistent with prior slope measurements in the similar Two Micron All-Sky Survey J band, as well as with predictions from the BaSTI isochrone suite. We use the new TRGB slope estimate to flatten the 2D TRGB feature and measure a (blinded) TRGB distance relative to a set of fiducial TRGB colors, intended to represent the absolute fiducial calibrations expected from geometric anchors such as NGC 4258 and the Magellanic Clouds. In doing so, we empirically demonstrate that the TRGB can be used as a standardizable candle at the IR wavelengths accessible with JWST.

Keywords: James Webb Space Telescope, Galaxy stellar content, Distance indicators
Quantifying the Expanding and Cooling Effects into the Double Adiabatic Evolution of the Solar Wind Through the Expanding Box Model. One of the fundamental problems in space physics is the expansion dynamics of the solar wind, strongly correlated with collective plasma reactions, such as wave instabilities that tend to relax kinetic anisotropies. The expansion is in general described through the double adiabatic or Chew–Goldberger–Low (CGL) theory, which sets the main ideas and plasma expansion's major role in describing plasma cooling/heating dynamics. Here, using the expanding box model (EBM) we revisit the CGL description including plasma expansion. Our primary objective is to isolate the expanding effects into the conservation of the double adiabatic invariants, a key aspect of the CGL theory. Following the same approximations and assumptions as in EBM and CGL theory, we developed a CGL-like description in which the expansion modifies the conservation of the double adiabatic invariants. Our results show that the double adiabatic equations are no longer conserved if plasma cooling is introduced through the EBM, with explicit dependence on expanding parameters, magnetic field profiles, and velocity gradients. Solving the equations for different magnetic field and density profiles (obtained self-consistently through the equations), we compute the evolution of temperature anisotropy and plasma beta, which deviates from CGL predictions and empirical observations. This deviation is attributed to the plasma cooling effect induced by the expansion of the plasma. The results suggest that heating mechanisms even play a major role in counteracting plasma cooling during expansion.

Keywords: Stellar winds, Solar wind, Plasma astrophysics
Learning the Universe: GalactISM Simulations of Resolved Star Formation and Galactic Outflows across Main-sequence and Quenched Galactic Environments. We present a suite of six high-resolution chemodynamical simulations of isolated galaxies, spanning observed disk-dominated environments on the star-forming main sequence, as well as quenched, bulge-dominated environments. We compare and contrast the physics driving star formation and stellar feedback among the galaxies, with a view to modeling these processes in cosmological simulations. We find that the mass loading of galactic outflows is coupled to the clustering of supernova explosions, which varies strongly with the rate of galactic rotation Ω = v circ/R via the Toomre length, leading to smoother gas disks in the bulge-dominated galaxies. This sets an equation of state in the star-forming gas that also varies strongly with Ω, so that the bulge-dominated galaxies have higher midplane densities, lower velocity dispersions, and higher molecular gas fractions than their main-sequence counterparts. The star formation rate in five out of six galaxies is independent of Ω and is consistent with regulation by the midplane gas pressure alone. In the sixth galaxy, which has the most centrally concentrated bulge and thus the highest Ω, we reproduce dynamical suppression of the star formation efficiency in agreement with observations. This produces a transition away from pressure-regulated star formation.

Keywords: Lenticular galaxies, Hydrodynamical simulations, Stellar feedback, Spiral galaxies, Disk galaxies, Galaxy properties, Galaxy structure, Galactic and extragalactic astronomy, Star formation, Interstellar medium, Galaxy processes
The Manhattan Suite: Accelerated Galaxy Evolution in the Early Universe. Observational advances have allowed the detection of galaxies, protoclusters, and galaxy clusters at higher and higher redshifts, opening a new view into extreme galaxy evolution. I present an argument that the high-redshift, massive galaxies discovered over the last decade are really the most massive galaxies within protocluster cores of galaxy clusters at z ∼ 2, and that they are the partial descendants of same galaxies discovered by JWST at z ∼ 9. To that end, I present The Manhattan Suite, a set of 100 high resolution zoom-in simulations of the most massive galaxy clusters, out to 9 R vir, selected at z = 2 from a (1.5 cGpc)3 parent volume, and simulated using the SIMBA model. Unlike other cluster suites, my selection at z = 2 ensures that these systems are biased in a similar fashion to observations, in that they should be the brightest and the most massive by construction at z ≳ 2. I show that my sample is able to reproduce extremely star-bursting protoclusters such as SPT2349-56, high-redshift galaxy clusters XLSSC122 and JKCS041, and the wealth of massive (sometimes quenched) galaxies at z ≳ 3 and up to z ∼ 9. I argue that these systems are intimately linked, and represent the same evolutionary history.

Keywords: Protoclusters, High-redshift galaxies, Astronomical simulations, High-redshift galaxy clusters
On the Physical Nature of Lyα Transmission Spikes in High-redshift Quasar Spectra. We investigate Lyman-alpha (Lyα) transmission spikes at 5.2 &lt; z &lt; 6.8 using synthetic quasar spectra from the "Cosmic Reionization on Computers" simulations. We focus on understanding the relationship between these spikes and the properties of the intergalactic medium (IGM). Disentangling the complex interplay between IGM physics and the influence of galaxies on the generation of these spikes presents a significant challenge. To address this, we employ Explainable Boosting machines, an interpretable machine learning algorithm, to quantify the relative impact of various IGM properties on the Lyα flux. Our findings reveal that gas density is the primary factor influencing absorption strength, followed by the intensity of background radiation and the temperature of the IGM. Ionizing radiation from local sources (i.e., galaxies) appears to have a minimal effect on Lyα flux. The simulations show that transmission spikes predominantly occur in regions of low gas density. Our results challenge recent observational studies suggesting the origin of these spikes in regions with enhanced radiation. We demonstrate that Lyα transmission spikes are largely a product of the large-scale structure, of which galaxies are biased tracers.

Keywords: Reionization, Lyman alpha forest, Intergalactic medium
Energy-dependent and Energy-integrated Two-moment General-relativistic Neutrino Transport Simulations of a Hypermassive Neutron Star. We compare two-moment-based energy-dependent and three variants of energy-integrated neutrino transport general-relativistic magnetohydrodynamics simulations of a hypermassive neutron star. To study the impacts due to the choice of the neutrino transport schemes, we perform simulations with the same setups and input neutrino microphysics. We show that the main differences between energy-dependent and energy-integrated neutrino transport are found in the disk and ejecta properties, as well as in the neutrino signals. The properties of the disk surrounding the neutron star and the ejecta in energy-dependent transport are very different from the ones obtained using energy-integrated schemes. Specifically, in the energy-dependent case, the disk is more neutron-rich at early times and becomes geometrically thicker at later times. In addition, the ejecta is more massive and, on average, more neutron-rich in the energy-dependent simulations. Moreover, the average neutrino energies and luminosities are about 30% higher. Energy-dependent neutrino transport is necessary if one wants to better model the neutrino signals and matter outflows from neutron star merger remnants via numerical simulations.

Keywords: Neutron stars, Neutrino astronomy
Reconstructing the Genealogy of LIGO-Virgo Black Holes. We propose a Bayesian inference framework to predict the merger history of LIGO-Virgo binary black holes (BHs), whose binary components may have undergone hierarchical mergers in the past. The framework relies on numerical relativity predictions for the mass, spin, and kick velocity of the remnant BHs. This proposed framework computes the masses, spins, and kicks imparted to the remnant of the parent binaries, given the initial masses and spin magnitudes of the binary constituents. We validate our approach by performing an "injection study" based on a constructed sequence of hierarchically formed binaries. Noise is added to the final binary in the sequence, and the parameters of the "parent" and "grandparent" binaries in the merger chain are then reconstructed. This method is then applied to three GWTC-3 events: GW190521, GW200220_061928, and GW190426_190642. These events were selected because at least one of the binary companions lies in the putative pair-instability supernova mass gap, in which stellar processes alone cannot produce BHs. Hierarchical mergers offer a natural explanation for the formation of BHs in the pair-instability mass gap. We use the backward evolution framework to predict the parameters of the parents of the primary companion of these three binaries. For instance, the parent binary of GW190521 has masses  72‑22+32M⊙  and  31‑23+24M⊙  within the 90% credible interval. Astrophysical environments with escape speeds ≥100 km s‑1 are preferred sites to host these events. Our approach can be readily applied to future high-mass gravitational wave events to predict their formation history under the hierarchical merger assumption.

Keywords: Gravitational waves, Bayesian statistics, Stellar mass black holes, Star clusters