adsabs/SciX_UAT_keywords huggingface dataset:
NEOMOD: A New Orbital Distribution Model for Near-Earth Objects

Near-Earth Objects (NEOs) are a transient population of small bodies with orbits near or in the terrestrial planet region. They represent a mid-stage in the dynamical cycle of asteroids and comets, which starts with their removal from the respective source regions-the main belt and trans-Neptunian scattered disk-and ends as bodies impact planets, disintegrate near the Sun, or are ejected from the solar system. Here we develop a new orbital model of NEOs by numerically integrating asteroid orbits from main-belt sources and calibrating the results on observations of the Catalina Sky Survey. The results imply a size-dependent sampling of the main belt with the ν 6 and 3:1 resonances producing ≃30% of NEOs with absolute magnitudes H = 15 and ≃80% of NEOs with H = 25. Hence, the large and small NEOs have different orbital distributions. The inferred flux of H < 18 bodies into the 3:1 resonance can be sustained only if the main-belt asteroids near the resonance drift toward the resonance at the maximal Yarkovsky rate (≃2 × 10-4 au Myr-1 for diameter D = 1 km and semimajor axis a = 2.5 au). This implies obliquities θ ≃ 0° for a < 2.5 au and θ ≃ 180° for a > 2.5 au, both in the immediate neighborhood of the resonance (the same applies to other resonances as well). We confirm the size-dependent disruption of asteroids near the Sun found in previous studies. An interested researcher can use the publicly available NEOMOD Simulator to generate user-defined samples of NEOs from our model.

Keywords: near-earth objects
The Age-Metallicity-Specific Orbital Energy Relation for the Milky Way's Globular Cluster System Confirms the Importance of Accretion for Its Formation

Globular clusters can form inside their host galaxies at high redshift when gas densities are higher and gas-rich mergers are common. They can also form inside lower-mass galaxies that have since been accreted and tidally disrupted, leaving their globular cluster complement bound to higher-mass halos. We argue that the age-metallicity-specific orbital energy relation in a galaxy's globular cluster system can be used to identify its origin. Gas-rich mergers should produce tightly bound systems in which metal-rich clusters are younger than metal-poor clusters. Globular clusters formed in massive disks and then scattered into a halo should have no relationship between age and specific orbital energy. Accreted globular clusters should produce weakly bound systems in which age and metallicity are correlated with eachother but inversely correlated with specific orbital energy. We use precise relative ages, self-consistent metallicities, and space-based proper motion-informed orbits to show that the Milky Way's metal-poor globular cluster system lies in a plane in age-metallicity-specific orbital energy space. We find that relatively young or metal-poor globular clusters are weakly bound to the Milky Way, while relatively old or metal-rich globular clusters are tightly bound to the Galaxy. While metal-rich globular clusters may be formed either in situ or ex situ, our results suggest that metal-poor clusters are formed outside of the Milky Way in now-disrupted dwarf galaxies. We predict that this relationship between age, metallicity, and specific orbital energy in a L* galaxy's globular cluster system is a natural outcome of galaxy formation in a ΛCDM universe.

Keywords: galaxy formation; globular star clusters; milky way dynamics; milky way formation; milky way stellar halo
The Chemical Enrichment of the Milky Way Disk Evaluated Using Conditional Abundances

Chemical abundances of Milky Way disk stars are empirical tracers of its enrichment history. However, they capture joint-information that is valuable to disentangle. In this work, we quantify how individual abundances evolve across the present-day Galactic radius, at fixed supernovae contribution ([Fe/H], [Mg/Fe]). We use 18,135 Apache Point Observatory Galactic Evolution Experiment Data Release 17 red clump stars and 7943 GALactic Archaeology with HERMES Data Release 3 main-sequence stars to compare the abundance distributions conditioned on ([Fe/H], [Mg/Fe]) across 3-13 kpc and 6.5-9.5 kpc, respectively. We examine 15 elements: C, N, Al, K (light), O, Si, S, Ca, (α), Mn, Ni, Cr, Cu, (iron-peak) Ce, Ba (s-process) and Eu (r-process). We find that the conditional neutron-capture and light elements most significantly trace variations in the disk's enrichment history, with absolute conditional radial gradients ≤0.03 dex kpc-1. The other elements studied have absolute conditional gradients ≲0.01 dex kpc-1. We uncover structured conditional abundance variations with [Fe/H] for the low-α, but not the high-α , sequence. The average scatter between the mean conditional abundances at different radii is σ intrinsic ≈ 0.02 dex (Ce, Eu, Ba σ intrinsic > 0.05 dex). These results serve as a measure of the magnitude via which different elements trace Galactic radial enrichment history once fiducial supernovae correlations are accounted for. Furthermore, we uncover subtle systematic variations in moments of the conditional abundance distributions and bimodal differences in [Al/Fe]. These suggest a nonuniform enrichment of each chemical cell, and will presumably constrain chemical evolution models of the Galaxy.

Keywords: milky way galaxy; milky way disk; stellar abundances; astrostatistics techniques; chemical abundances
The Diverse Morphologies and Structures of Dwarf Galaxies Hosting Optically Selected Active Massive Black Holes

We present a study of 41 dwarf galaxies hosting active massive black holes (BHs) using Hubble Space Telescope observations. The host galaxies have stellar masses in the range of M⋆ ∼ 108.5-109.5 M⊙ and were selected to host active galactic nuclei (AGNs) based on narrow emission line ratios derived from Sloan Digital Sky Survey spectroscopy. We find a wide range of morphologies in our sample including both regular and irregular dwarf galaxies. We fit the HST images of the regular galaxies using GALFIT and find that the majority are disk-dominated with small pseudobulges, although we do find a handful of bulge-like/elliptical dwarf galaxies. We also find an unresolved source of light in all of the regular galaxies, which may indicate the presence of a nuclear star cluster and/or the detection of AGN continuum. Three of the galaxies in our sample appear to be Magellanic-type dwarf irregulars and two galaxies exhibit clear signatures of interactions/mergers. This work demonstrates the diverse nature of dwarf galaxies hosting optically selected AGNs. It also has implications for constraining the origin of the first BH seeds using the local BH occupation fraction at low masses—we must account for the various types of dwarf galaxies that may host BHs.

Keywords: dwarf galaxies; active galactic nuclei; active galaxies; hst photometry; intermediate-mass black holes; agn host galaxies
Anomalous Flux Event in the TESS Sector 43 Light Curve of the White Dwarf Photometric Standard HZ 4 was Caused by a Passing Asteroid

Frymire & Ardila reported an anomalous flux variation in the Transiting Exoplanet Survey Satellite (TESS) Sector 43 light curve of the white dwarf HZ 4. We show that this flux variation was caused by the main-belt asteroid 4382 Stravinsky traversing the nearby TESS pixels, and it is therefore not a cause for concern regarding the continued use of HZ 4 as a photometric standard star.

Keywords: astronomy data analysis; asteroids; photometric standard stars; small solar system bodies; white dwarf stars
Comparison of Anomalous and Galactic Cosmic-Ray Oxygen at 1 au during 1997-2020

Using quiet-time measurements of element oxygen within the energy range 7.3-237.9 MeV nuc-1 from the ACE spacecraft at 1 au, we compare the energy spectra and intensities of anomalous and Galactic cosmic rays (ACRs and GCRs, respectively) during 1997-2020. Our analysis shows that the transition from the ACR-dominated spectrum to the GCR-dominated spectrum occurs at energies ~15 to ~35 MeV nuc-1, and the transition energy Et is found to be well anticorrelated with varying solar activity. This is the first study of ACR-GCR transition energy dependence on the solar cycle variation. At energies below Et, the index of the power-law ACR-dominated spectrum (γ1) ranges from -2.0 to -0.5, whereas the GCR-dominated spectrum has a power-law index (γ2) changing from 0.3 to 0.8 at energies ranging from Et to 237.9 MeV nuc-1. Both γ1 and γ2 are positively correlated with solar activity. In addition, during the solar cycle 24/25 minimum period, the peak GCR intensity observed by ACE spacecraft is about 8% above its 2009 value, setting a new record since the space age, while the peak ACR intensity is almost similar to that of the previous two solar cycles with the same pattern of solar magnetic polarity, indicating a different modulation mechanism between ACRs and GCRs.

Keywords: cosmic rays; heliosphere; solar cycle; particle astrophysics; solar physics
Quantifying Solar Radiation Pressure Effects on Dust at Small Heliocentric Distances

The dynamics of dust grains has traditionally been modeled under the assumption that the ratio of the opposing solar radiation pressure and gravitational forces is fixed for an individual, unchanging grain. However, at small heliocentric distances, this assumption is inaccurate, as the variation in radiation pressure force with heliocentric distance does not follow an inverse square law there, as the Sun cannot be approximated as a point source of light. To correct for this, we have calculated the required correction to assumed radiation pressure force values, taking into account the decrease in both the visible solar area and in the radial solar radiation force components. We present here an empirical fit to this correction, for heliocentric distances 0.028–1.00 au. This correction may be used to more accurately simulate dust motion near the Sun.

Keywords: comets; near-sun comets; comet dust tails; solar f corona; solar system; zodiacal cloud
Brightness Fluctuation Spectra of Sun-like Stars. I. The Mid-frequency Continuum

We analyze space-based time-series photometry of Sun-like stars, mostly in the Pleiades, but also field stars and the Sun itself. We focus on timescales between roughly 1 hr and 1 day. In the corresponding frequency band these stars display brightness fluctuations with a decreasing power-law continuous spectrum. K2 and Kepler observations show that the rms flicker due to this mid-frequency continuum (MFC) can reach almost 1%, approaching the modulation amplitude from active regions. The MFC amplitude varies by a factor up to 40 among Pleiades members with similar Teff, depending mainly on the stellar Rossby number Ro. For Ro ≤ 0.04, the mean amplitude is roughly constant at about 0.4%; at larger Ro the amplitude decreases rapidly, shrinking by about two orders of magnitude for Ro ≃ 1. Among stars, the MFC amplitude correlates poorly with that of modulation from rotating active regions. Among field stars observed for 3 yr by Kepler, the quarterly average modulation amplitudes from active regions are much more time variable than the quarterly MFC amplitudes. We argue that the process causing the MFC is largely magnetic in nature and that its power-law spectrum comes from magnetic processes distinct from the star's global dynamo, with shorter timescales. By analogy with solar phenomena, we hypothesize that the MFC arises from a (sometimes energetic) variant of the solar magnetic network, perhaps combined with rotation-related changes in the morphology of supergranules.

Keywords: stellar activity; stellar rotation; solar dynamo; supergranulation
Brought to Light. II. Revealing the Origins of Cloaked Spiral Features in Cluster Passive Dwarf Galaxies

In our companion paper (Brought to Light I: Michea et al.), we reveal spectacular spiral-galaxy-like features in deep optical imaging of nine Virgo early-type dwarf galaxies, hidden beneath a dominating smooth stellar disk. Using a new combination of approaches, we find that bar- and spiral-like features contribute 2.2%-6.4% of the total flux within 2 Reff. In this study, we conduct high-resolution simulations of cluster harassment of passive dwarf galaxies. Following close pericenter passages of the cluster core, tidal triggering generates features in our model disks that bear a striking resemblance to the observed features. However, we find the disks must be highly rotationally supported (Vpeak/σ0 ∼ 3), much higher than typically observed. We propose that some early-type dwarfs may contain a few percent of their mass in a cold, thin disk that is buried in the light of a hot, diffuse disk and only revealed when they undergo tidal triggering. The red optical colors of our sample do not indicate any recent significant star formation, and our simulations show that very plunging pericenter passages (rperi < 0.25rvir) are required for tidal triggering. Thus, many cluster early-type dwarfs with less-plunging orbits may host a yet-undetected cold stellar disk component. We discuss possible origin scenarios and consider why similar-mass star-forming galaxies in the field are significantly more thin-disk dominated than in our cluster sample.

Keywords: galaxy clusters; galaxy disks; galaxy dynamics; galaxy dark matter halos; galaxy environments; galaxy encounters; n-body simulations; dwarf galaxies; galaxy stellar disks
Testing He II Emission from Wolf–Rayet Stars as a Dust Attenuation Measure in Eight Nearby Star-forming Galaxies

The ability to determine galaxy properties such as masses, ages, and star formation rates robustly is critically limited by the ability to measure dust attenuation accurately. Dust reddening is often characterized by comparing observations to models of either nebular recombination lines or the UV continuum. Here, we use a new technique to measure dust reddening by exploiting the He II λ1640 and λ4686 emission lines originating from the stellar winds of Wolf–Rayet stars. The intrinsic line ratio is determined by atomic physics, enabling an estimate of the stellar reddening similar to how the Balmer lines probe gas-emission reddening. The He II line ratio is measured from UV and optical spectroscopy using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope for eight nearby galaxies hosting young massive star clusters. We compare our results to dust reddening values estimated from UV spectral slopes and from Balmer line ratios and find tentative evidence for systematic differences. The reddening derived from the He II lines tends to be higher, whereas that from the UV continuum tends to be lower. A larger sample size is needed to confirm this trend. If confirmed, this may indicate an age sequence probing different stages of dust clearing. Broad He II lines have also been detected in galaxies more distant than in our sample, providing the opportunity to estimate the dust reddening of the youngest stellar populations out to distances of ∼100 Mpc.

Keywords: star formation; star clusters; interstellar dust extinction; wolf-rayet stars
Comparing the Performance of a Solar Wind Model from the Sun to 1 au Using Real and Synthetic Magnetograms

The input of the solar wind models plays a significant role in accurate solar wind predictions at 1 au. This work introduces a synthetic magnetogram produced from a dynamo model as an input for magnetohydrodynamics simulations. We perform a quantitative study that compares the space weather modeling framework (SWMF) results for the observed and synthetic solar magnetogram input. For each case, we compare the results for extreme ultraviolet images and extract the simulation data along the Earth trajectory to compare with in situ observations. We initialize the SWMF using the real and synthetic magnetograms for a set of Carrington rotations within solar cycles 23 and 24. Our results help quantify the ability of dynamo models to be used as input to solar wind models and thus provide predictions for the solar wind at 1 au.

Keywords: solar physics; magnetohydrodynamical simulations; solar wind; solar cycle; solar magnetic fields
Total r-process Yields of Milky Way Neutron Star Mergers

While it is now known that the mergers of double neutron star binary systems (NSMs) are copious producers of heavy elements, there remains much speculation about whether they are the sole or even principal site of rapid neutron-capture (r-process) nucleosynthesis, one of the primary ways in which heavy elements are produced. The occurrence rates, delay times, and galactic environments of NSMs hold sway over estimating their total contribution to the elemental abundances in the solar system and the Galaxy. Furthermore, the expected elemental yields of NSMs may depend on the merger parameters themselves—such as their stellar masses and radii—which are not currently considered in many galactic chemical evolution models. Using the characteristics of the observed sample of double neutron star (DNS) systems in the Milky Way as a guide, we predict the expected nucleosynthetic yields that a population of DNSs would produce upon merger, and we compare that nucleosynthetic signature to the heavy-element abundance pattern of solar system elements. We find that with our current models, the present DNS population favors the production of lighter r-process elements, while underproducing the heaviest elements relative to the solar system. This inconsistency could imply an additional site for the heaviest elements or a population of DNSs much different from that observed today.

Keywords: nucleosynthesis; r-process; neutron stars; chemical abundances; galaxy chemical evolution
Differential Source Count for Gamma-Ray Bursts

Different forms of long gamma-ray burst (GRB) luminosity functions are considered on the basis of an explicit physical model. The inferred flux distributions are compared with the observed ones from two samples of GRBs, Swift and Fermi GBM. The best-fit parameters of the luminosity functions are found, and the physical interpretations are discussed. The results are consistent with the observation of a comparable number of flat-phase afterglows and monotonically decreasing ones.

Keywords: gamma-ray bursts
Modeling Photoionized Turbulent Material in the Circumgalactic Medium. III. Effects of Corotation and Magnetic Fields

Absorption-line measurements of the circumgalactic medium (CGM) display a highly nonuniform distribution of lower ionization state species accompanied by more widespread higher ionization state material. This suggests that the CGM is a dynamic, multiphase medium, such as arises in the presence of turbulence. To better understand this evolution, we perform hydrodynamic and magnetohydrodynamic (MHD) simulations of the CGM surrounding Milky Way-like galaxies. In both cases, the CGM is initially in hydrostatic balance in a 1012 M ⊙ dark matter gravitational potential, and the simulations include rotation in the inner halo and turbulence that decreases radially. They also track ionizations, recombinations, and species-by-species radiative cooling in the presence of the redshift-zero UV background, employing the MAIHEM nonequilibrium chemistry package. We find that after 9 Gyr of evolution, the presence of a magnetic field leads to an overall hotter CGM, with cool gas in the center where magnetic pressure dominates. While the non-MHD run produces more cold clouds overall, we find similar Si IV/O VI and N V/O VI ratios between the MHD and non-MHD runs, which are both very different from their equilibrium values. The non-MHD halo develops cool, low angular momentum filaments above the central disk, in comparison to the MHD run that has more efficient angular momentum transport, especially for the cold gas, which forms a more ordered and extended disk late into its evolution.

Keywords: astrochemistry; circumgalactic medium; magnetic fields
An Ultradeep Multiband VLA Survey of the Faint Radio Sky (COSMOS-XS): Source Catalog and Number Counts

We present ultradeep, matched-resolution Karl G. Jansky Very Large Array observations at 10 and 3 GHz in the COSMOS field: the COSMOS-XS survey. The final 10 and 3 GHz images cover ∼16 and $\sim 180\,{\mathrm{arcmin}}^{2}$ and reach median rms values at the phase center of 0.41 and 0.53 μJy beam-1, respectively. Both images have an angular resolution of ∼2"0. To account for the spectral shape and resolution variations across the broad bands, we image all data with a multiscale, multifrequency synthesis algorithm. We present source catalogs for the 10 and 3 GHz image with 91 and 1498 sources, respectively, above a peak brightness threshold of 5σ. We present source counts with completeness corrections included that are computed via Monte Carlo simulations. Our corrected counts at 3 GHz are consistent within the uncertainties with other results at 3 and 1.4 GHz but extend to fainter flux densities than previous direct detections. The 3 GHz number counts exceed the counts predicted by the semiempirical simulations developed in the framework of the SKA Simulated Skies project, consistent with previous P(D) analyses. Our source counts suggest a steeper luminosity function evolution for faint star-forming sources. The semiempirical Tiered Radio Extragalactic Continuum Simulation predicts this steeper evolution and is in better agreement with our results at 10 and 3 GHz within the expected variations from cosmic variance. In summary, the multiband, matched-resolution COSMOS-XS survey in the COSMOS field provides a high-resolution view of the ultrafaint radio sky that can help guide next-generation radio facilities.

Keywords: radio source counts; radio source catalogs; radio continuum emission
Spatially Resolved Study of Recombining Plasma in W49B Using XMM-Newton

W49B is the youngest supernova remnant (SNR) to date that exhibits recombining plasma. The two prevailing theories of this overionization are rapid cooling via adiabatic expansion or through thermal conduction with an adjacent cooler medium. To constrain the origin of the recombining plasma in W49B, we perform a spatially resolved spectroscopic study of deep XMM-Newton data across 46 regions. We adopt a three-component model (with one interstellar medium and two ejecta components), and we find that recombining plasma is present throughout the entire SNR, with increasing overionization from east to west. The latter result is consistent with previous studies, and we attribute the overionization in the west to adiabatic expansion. However, our findings depart from these prior works, as we find evidence of overionization in the east as well. As the SNR is interacting with molecular material there, we investigate the plausibility of thermal conduction as the origin of the rapid cooling. Based on estimated timescales, we show that both large- and small-scale thermal conduction can explain the observed overionization of the hotter ejecta. However, overionization of the cooler ejecta is only possible through small-scale thermal conduction resulting in evaporation of embedded, dense clouds with sizes ≲1 pc.

Keywords: supernova remnants; x-ray astronomy; radiative recombination; interstellar medium; dense interstellar clouds