adsabs/SciX_UAT_keywords huggingface dataset:
Joint Survey Processing. II. Stellar Proper Motions in the COSMOS Field from Hubble Space Telescope ACS and Subaru Telescope HSC Observations

We analyze stellar proper motions in the COSMOS field to assess the presence of bulk motions. At bright magnitudes (G-band 18.5-20.76 AB), we use the proper motions of 1010 stars in the Gaia DR2 catalog. At the faint end, we compute proper motions of 11,519 pointlike objects at i-band magnitudes 19-25 AB using Hubble ACS and Subaru HSC data, which span two epochs about 11 yr apart. In order to measure these proper motions with unprecedented accuracy at faint magnitudes, we developed a foundational set of astrometric tools that will be required for joint survey processing of data from the next generation of optical/infrared surveys. The astrometric grids of Hubble ACS and Subaru HSC mosaics were corrected at the catalog level using proper motion-propagated and parallax-corrected Gaia DR2 sources. These astrometric corrections were verified using compact extragalactic sources. Upon comparison of our measured proper motions with Gaia DR2, we estimate the uncertainties in our measurements to be ~2-3 mas yr-1 axis-1, down to 25.5 AB mag. We correct proper motions for the mean motion of the Sun, and we find that late-type main-sequence stars predominantly in the thin disk in the COSMOS field have space velocities mainly toward the Galactic center. We detect candidate high-velocity (≥220 km s-1) stars, six of them at ~0.4-6 kpc, from the Gaia sample, and five of them at ~20 kpc, from the faint star HSC and ACS sample. The sources from the faint star sample may be candidate halo members of the Sangarius stream.

Keywords: galaxy structure; galaxy stellar halos; proper motions; astrometry; catalogs; stellar streams
Tearing Modes in Partially Ionized Astrophysical Plasma

In many astrophysical environments the plasma is only partially ionized, and therefore the interaction of charged and neutral particles may alter both the triggering of reconnection and its subsequent dynamical evolution. We derive the tearing mode maximum growth rate for partially ionized plasmas in the cases of weak and strong coupling between the plasma and the neutrals. In addition, critical scalings for current sheet aspect ratios are presented in terms of Lundquist number and ion-neutral collision frequencies for which the tearing mode becomes fast, or ideal. In the decoupled regime the standard tearing mode is recovered with a small correction that depends on the ion-neutral collision frequency; in the intermediate regime collisions with neutrals are shown to stabilize current sheets, resulting in larger critical aspect ratios for ideal tearing to occur. In the coupled regime, the growth rate depends on the density ratio between ions and neutrals through the collision frequency between these two species.

Keywords: solar magnetic reconnection; plasma astrophysics; space plasmas
Bounds on Velocity-dependent Dark Matter-Proton Scattering from Milky Way Satellite Abundance

We use the latest measurements of the Milky Way satellite population from the Dark Energy Survey and Pan-STARRS1 to infer the most stringent astrophysical bound to date on velocity-dependent interactions between dark matter particles and protons. We model the momentum-transfer cross section as a power law of the relative particle velocity v with a free normalizing amplitude, σMT = σ0vn, to broadly capture the interactions arising within the nonrelativistic effective theory of dark matter-proton scattering. The scattering leads to a momentum and heat transfer between the baryon and dark matter fluids in the early universe, ultimately erasing structure on small physical scales and reducing the abundance of low-mass halos that host dwarf galaxies today. From the consistency of observations with the cold collisionless dark matter paradigm, using a new method that relies on the most robust predictions of the linear perturbation theory, we infer an upper limit on σ0 of 1.4 × 10-23, 2.1 × 10-19, and 1.0 × 10-12 cm2, for interaction models with n = 2, 4, and 6, respectively, for a dark matter particle mass of 10 MeV. These results improve observational limits on dark matter-proton scattering by orders of magnitude and thus provide an important guide for viable sub-GeV dark matter candidates.

Keywords: dark matter; galaxy dark matter halos
Kinetic-scale Current Sheets in Near-Sun Solar Wind: Properties, Scale-dependent Features and Reconnection Onset

We present statistical analysis of 11,200 proton kinetic-scale current sheets (CS) observed by the Parker Solar Probe during 10 days around the first perihelion. The CS thickness λ is in the range from a few to 200 km with the typical value around 30 km, while current densities are in the range from 0.1 to 10 μA m-2 with the typical value around 0.7 μA m-2. These CSs are resolved thanks to magnetic field measurements at 73-290 samples s-1 resolution. In terms of proton inertial length λ p , the CS thickness λ is in the range from about 0.1 to 10λ p with the typical value around 2λ p . The magnetic field magnitude does not substantially vary across the CSs, and accordingly the current density is dominated by the magnetic-field-aligned component. The CSs are typically asymmetric with statistically different magnetic field magnitudes at the CS boundaries. The current density is larger for smaller-scale CSs, J 0 ≈ 0.15 × (λ/100 km)-0.76 μA m-2, but does not statistically exceed the Alfvén current density J A corresponding to the ion-electron drift of the local Alfvén speed. The CSs exhibit remarkable scale-dependent current density and magnetic shear angles, ${J}_{0}/{J}_{A}\approx 0.17\times {(\lambda /{\lambda }_{p})}^{-0.67}$ and ${\rm{\Delta }}\theta \approx 21^\circ \times {(\lambda /{\lambda }_{p})}^{0.32}$ . Based on these observations and comparison to recent studies at 1 au, we conclude that proton kinetic-scale CSs in the near-Sun solar wind are produced by turbulence cascade, and they are automatically in the parameter range, where reconnection is not suppressed by the diamagnetic mechanism, due to their geometry dictated by turbulence cascade.

Keywords: solar wind; interplanetary turbulence
A Babcock-Leighton-type Solar Dynamo Operating in the Bulk of the Convection Zone

The toroidal magnetic field is assumed to be generated in the tachocline in most Babcock-Leighton (BL)-type solar dynamo models, in which the poloidal field is produced by the emergence and subsequent dispersal of sunspot groups. However, magnetic activity of fully convective stars and MHD simulations of global stellar convection have recently raised serious doubts regarding the importance of the tachocline in the generation of the toroidal field. In this study, we aim to develop a new BL-type dynamo model, in which the dynamo operates mainly within the bulk of the convection zone. Our 2D model includes the effect of solar-like differential rotation, one-cell meridional flow, near-surface radial pumping, strong turbulent diffusion, BL-type poloidal source, and nonlinear back-reaction of the magnetic field on its source with a vertical outer boundary condition. The model leads to a simple dipolar configuration of the poloidal field that has the dominant latitudinal component, which is wound up by the latitudinal shear within the bulk of the convection zone to generate the toroidal flux. As a result, the tachocline plays a negligible role in the model. The model reproduces the basic properties of the solar cycle, including (a) approximately 11 yr cycle period and 18 yr extended cycle period; (b) equatorward propagation of the antisymmetric toroidal field starting from high latitudes; and (c) polar field evolution that is consistent with observations. Our model opens the possibility for a paradigm shift in understanding the solar cycle to transition from the classical flux transport dynamo.

Keywords: solar dynamo; sunspot cycle; solar differential rotation
Substructure in the Globular Cluster Populations of the Virgo Cluster Elliptical Galaxies M84 and M86

We have carried out a search for substructure within the globular cluster (GC) systems of M84 (NGC 4374) and M86 (NGC 4406), two giant elliptical galaxies in the Virgo Cluster. We use wide-field (36' × 36'), multicolor broadband imaging to identify GC candidates in these two galaxies, as well as several other nearby lower-mass galaxies. Our analysis of the spatial locations of the GC candidates reveals several substructures, including a peak in the projected number density of GCs in M86 that is offset from the system center and may be at least partly due to the presence of the dwarf elliptical galaxy NGC 4406B, a bridge that connects the M84 and M86 GC systems, and a boxy isodensity contour along the southeast side of the M86 GC system. We divide our sample into red (metal-rich) and blue (metal-poor) GC candidates to look for differences in the spatial distributions of the two populations and find that the blue cluster candidates are the dominant population in each of the substructures we identify. We also incorporate the measurements from two radial velocity surveys of the GCs in the region and find that the bridge substructure is populated by GCs with a mix of velocities that are consistent with either M86 and M84, possibly providing further evidence for interaction signatures between the two galaxies.

Keywords: star clusters; giant elliptical galaxies; virgo cluster
Six Years of Luminous X-Ray Emission from the Strongly Interacting Yype-Ib SN2014C Captured by Chandra and NuSTAR

We present the first coordinated soft and hard 0.3-80 keV X-ray campaign of the extragalactic supernova SN2014C in the first ∼2307 days of its evolution. SN2014C initially appeared to be an ordinary type Ib explosion but evolved into a strongly-interacting hydrogen-rich SN IIn over ∼1 yr. We observed signatures of interaction with a dense medium across the X-ray spectrum, which revealed the presence of a ∼1-2M⊙ shell of material at ∼6 × 1016 cm from the progenitor. This finding challenges current understanding of hydrogen-poor core-collapse progenitor evolution. Potential scenarios to interpret these observations include (i) the ejection of the hydrogen envelope by the progenitor star in the centuries prior to the explosion; (ii) interaction of the fast Wolf-Rayet (WR) star wind with the slow, dense wind of the Red Super Giant phase, with an anomalously short WR phase.

Keywords: supernovae; stellar mass loss
Characterizing the Breakdown of Quasi-universality in Postmerger Gravitational Waves from Binary Neutron Star Mergers

The postmerger gravitational wave (GW) emission from a binary neutron star merger is expected to provide exciting new constraints on the dense-matter equation of state (EoS). Such constraints rely, by and large, on the existence of quasi-universal relations, which relate the peak frequencies of the postmerger GW spectrum to properties of the neutron star structure in a model-independent way. In this work, we report on violations of existing quasi-universal relations between the peak spectral frequency, f 2, and the stellar radius, for EoS models with backwards-bending slopes in their mass-radius relations (such that the radius increases at high masses). The violations are extreme, with variations in f 2 of up to ~600 Hz between EoSs that predict the same radius for a 1.4 M ⊙ neutron star but that have significantly different radii at higher masses. Quasi-universality can be restored by adding in a second parameter to the fitting formulae that depends on the slope of the mass-radius curve. We further find strong evidence that quasi-universality is better maintained for the radii of very massive stars (with masses 2 M ⊙). Both statements imply that f 2 is mainly sensitive to the high-density EoS. Combined with observations of the binary neutron star inspiral, these generalized quasi-universal relations can be used to simultaneously infer the characteristic radius and slope of the neutron star mass-radius relation.

Keywords: neutron stars; gravitational waves
Direction of Parsec-scale Jets for 9220 Active Galactic Nuclei

The direction of parsec-scale jets in active galactic nuclei (AGNs) is essential information for many astrophysical and astrometric studies, including linear polarization and magnetic field structure, frequency-dependent synchrotron opacity, proper motion, and reference-frame alignment. We developed a rigorous, simple, and completely automated method to measure the directions from calibrated interferometric visibility data at frequencies ranging from 1.4 to 86 GHz. We publish the results for 9220 AGNs with the typical accuracy below 10°. An internal check of the method comparing the directions between different observing frequencies as well as with previous publications verifies the robustness of the measured values.

Keywords: active galactic nuclei; radio jets; very long baseline interferometry; radio cores
Mg II Absorbers in High-resolution Quasar Spectra. I. Voigt Profile Models

We present the Voigt profile (VP) models, column densities, Doppler b parameters, kinematics, and distribution of components for 422 Mg II absorbers found in a survey of 249 HIRES and UVES quasar spectra. The equivalent width range of the sample is 0.006 ≤ Wr(2796) ≤ 6.23 Å and the redshift range is 0.19 ≤ z ≤ 2.55, with a mean of $\langle z\rangle =1.18$ . Based on historical precedent, we classified 180 absorbers as weak systems (Wr(2796) < 0.3 Å) and 242 as strong systems (Wr(2796) ≥ 0.3 Å). Assuming a minimum number of significant components per system, the VP fitting, yielded a total of 2989 components, with an average of 2.7 and 10.3 components found for the weak and strong Mg II subsamples, respectively. The VP component line density for the full sample is 8.62 ± 0.23 clouds Å-1. The distribution of VP component column density over the range 12.4 ≤ log N(Mg II) ≤ 17.0 cm-2 is well modeled with a power-law slope of -1.45 ± 0.01. The median Doppler b parameters are 4.5 ± 3.5 km s-1, 6.0 ± 4.5 km s-1, and 5.7 ± 4.4 km s-1 for the weak, strong, and full samples. We modeled the probability of component velocity splitting (the two-point velocity correlation function) of our full sample using a three-component composite Gaussian function. Our resulting velocity dispersions are σ1 = 25.4 km s-1, σ2 = 68.7 km s-1, and σ3 = 207.1 km s-1. These data provide an excellent database for studying the cosmic evolution of Mg II absorber kinematic evolution.

Keywords: circumgalactic medium; quasar absorption line spectroscopy; galaxy kinematics
Electron Injection via Modified Diffusive Shock Acceleration in High-Mach-number Collisionless Shocks

The ability of collisionless shocks to efficiently accelerate nonthermal electrons via diffusive shock acceleration (DSA) is thought to require an injection mechanism capable of preaccelerating electrons to high enough energy where they can start crossing the shock front potential. We propose, and show via fully kinetic plasma simulations, that in high-Mach-number shocks electrons can be effectively injected by scattering in kinetic-scale magnetic turbulence produced near the shock transition by the ion Weibel, or current filamentation, instability. We describe this process as a modified DSA mechanism where initially thermal electrons experience the flow velocity gradient in the shock transition and are accelerated via a first-order Fermi process as they scatter back and forth. The electron energization rate, diffusion coefficient, and acceleration time obtained in the model are consistent with particle-in-cell simulations and with the results of recent laboratory experiments where nonthermal electron acceleration was observed. This injection model represents a natural extension of DSA and could account for electron injection in high-Mach-number astrophysical shocks, such as those associated with young supernova remnants and accretion shocks in galaxy clusters.

Keywords: cosmic ray sources; supernova remnants; laboratory astrophysics
Interferometric Closure Phase Uncertainties in the Low Signal-to-noise Ratio Regime

Closure phases are critical in astronomical interferometry. However, their uncertainties are difficult to compute numerically. We provide a method to efficiently compute interferometric closure phase distributions in terms of an approximate distribution that is valid in the low signal-to-noise ratio regime. This is done by first showing that the true phase distribution is well approximated by the von Mises distribution, then performing a convolution of three von Mises distributions. The resulting approximation superior to the normal distribution for all signal-to-noise ratios and, being fully analytic, allows for fast computations in statistical algorithms.

Keywords: interferometers; astronomical instrumentation; astrostatistics
Unresolved Sources Naturally Contribute to PeV Gamma-Ray Diffuse Emission Observed by Tibet ASγ

The Tibet ASγ experiment provided the first measurement of the total diffuse gamma-ray emission from the Galactic disk in the sub-PeV energy range. Based on the analysis of TeV sources included in the H.E.S.S. Galactic Plane Survey catalog, we predict the expected contribution of unresolved pulsar-powered sources in the two angular windows of the Galactic plane observed by Tibet ASγ. We show that the sum of this additional diffuse component due to unresolved sources and the truly diffuse emission, due to cosmic-ray interaction with the interstellar medium, well saturates the Tibet data, without the need to introduce a progressive hardening of the cosmic-ray spectrum toward the Galactic center.

Keywords: gamma-ray astronomy
Whither or Wither the Sulfur Anomaly in Planetary Nebulae?

We present a thorough investigation of the long-standing sulfur anomaly enigma. Our analysis uses chemical abundances from the most extensive data set available for 126 planetary nebulae (PNs) with improved accuracy and reduced uncertainties from a 10° × 10° Galactic bulge region. By using argon as a superior PN metallicity indicator, the anomaly is significantly reduced and better constrained. For the first time in PNs we show sulfur α-element lockstep with both oxygen and argon. We dispel hypotheses that the anomaly originates from underestimation of higher sulfur ionization stages. Using a machine-learning approach, we show that earlier ionization correction factor schemes contributed significantly to the anomaly. We find a correlation between the sulfur anomaly and the age/mass of PN progenitors, with the anomaly either absent or significantly reduced in PNs with young progenitors. Despite inherent challenges and uncertainties, we link this to PN dust chemistry, noting those with carbon-dust chemistry show a more pronounced anomaly. By integrating these findings, we provide a plausible explanation for the residual, reduced sulfur anomaly and propose its potential as an indicator of relative galaxy age compositions based on PNs.

Keywords: planetary nebulae nuclei; galactic abundances; planetary nebulae
Efficient Long-range Active Galactic Nuclei (AGNs) Feedback Affects the Low-redshift Lyα Forest

Active galactic nuclei (AGNs) feedback models are generally calibrated to reproduce galaxy observables such as the stellar mass function and the bimodality in galaxy colors. We use variations of the AGN feedback implementations in the IllustrisTNG (TNG) and SIMBA cosmological hydrodynamic simulations to show that the low-redshift Lyα forest can provide constraints on the impact of AGN feedback. We show that TNG overpredicts the number density of absorbers at column densities N HI < 1014 cm-2 compared to data from the Cosmic Origins Spectrograph (in agreement with previous work), and we demonstrate explicitly that its kinetic feedback mode, which is primarily responsible for galaxy quenching, has a negligible impact on the column density distribution (CDD) of absorbers. In contrast, we show that the fiducial SIMBA model, which includes AGN jet feedback, is the preferred fit to the observed CDD of the z = 0.1 Lyα forest across 5 orders of magnitude in column density. We show that the SIMBA results with jets produce a quantitatively better fit to the observational data than the SIMBA results without jets, even when the ultraviolet background is left as a free parameter. AGN jets in SIMBA are high speed, collimated, weakly interacting with the interstellar medium (via brief hydrodynamic decoupling), and heated to the halo virial temperature. Collectively these properties result in stronger long-range impacts on the intergalactic medium when compared to TNG's kinetic feedback mode, which drives isotropic winds with lower velocities at the galactic radius. Our results suggest that the low-redshift Lyα forest provides plausible evidence for long-range AGN jet feedback.

Keywords: cosmology; extragalactic astronomy; intergalactic gas; lyman alpha forest; active galactic nuclei; astrophysical black holes
On the Two-body Problem with Mass Loss Depending on Both Time and Radius Vector

The dynamics of the two-body problem with general mass-loss functions that depend on both the independent variable and the radial distance are studied. These functions have been considered by Docobo and coworkers to explain the so-called "periastron" effect. By means of some appropriate changes of variables we reduce the integration of this problem to a perturbed harmonic oscillator that is solved by means of the Krylov-Bogolioubov (KB) averaging method. By using the fact that the KB method provides approximate solutions that are first-order accurate in the small parameter ϵ in intervals of length 1/ϵ, we may get first-order accurate solutions for all physical time t ≥ 0 and therefore to study the asymptotic behavior of solutions for all t ≥ 0. These results extend previous studies of the authors for the first Gylden-Mestchersky problem.

Keywords: celestial mechanics; stellar mass loss
Supernova Ejecta with Crystalline Silicate Dust in the Supernova Remnant MSH 15–52

IRAS 15099-5856 in the young supernova remnant (SNR) MSH 15‑52 is the first and only SNR-associated object with crystalline silicate dust detected so far, although its nature and the origin of the crystalline silicate are still unclear. In this paper, we present high-resolution mid-infrared (MIR) imaging observations of the bright central compact source IRS1 of IRAS 15099-5856 to study the spatial distributions of gas and dust and the analysis of its Spitzer MIR spectrum to explore the origin of IRS1. The MIR images obtained with the T-ReCS attached on the Gemini South telescope show a complicated, inhomogeneous morphology of IRS1 with bright clumps and diffuse emission in [Ne II] 12.81 μm and Qa 18.30 μm, which confirms that IRS1 is an extended source externally heated by the nearby O star Muzzio 10, a candidate for the binary companion of the progenitor star. The Spitzer MIR spectrum reveals several ionic emission lines including a strong [Ne II] 12.81 μm line, but no hydrogen line is detected. We model the spectrum using the photoionization code CLOUDY with varying elemental composition. The elemental abundance of IRS1 derived from the model is close to that of supernova (SN) ejecta with depleted hydrogen and enhanced metals, particularly neon, argon, and iron. Our results imply that IRS1 originates from the SN ejecta and suggest the possibility of the formation of crystalline silicate in newly formed SN dust.

Keywords: infrared spectroscopy; interstellar medium; supernova remnants