adsabs/SciX_UAT_keywords huggingface dataset:
Pre-main-sequence Stars in Taurus: Comparison of Magnetic and Nonmagnetic Model Fits to the Low-mass Stars

Stellar associations should be co-eval, but some associations exhibit apparently discrepant ages: M stars appear younger than FG stars. Among M stars in the Upper Sco association (age ≈ 11 Myr), magnetic effects have been shown to slow down evolution of the lowest mass stars, thereby alleviating the age discrepancy. A recent study of pre-main-sequence (PMS) stars in the much younger Taurus star-forming region (SFR) suggest that an age discrepancy may also exist there. Our goal is to compare two approaches to magnetic/nonmagnetic modeling of the Taurus stars. In one approach, Simon et al. concluded that an age discrepancy exists, but it can be resolved by magnetic models if one imposes an "equipartition condition" on the photospheric field of each star. In this paper, we examine an independent sample of seven Taurus PMS stars reported by Rizzuto et al. Our approach to modeling magneto-convection imposes no condition on the photospheric field strength. We find that nonmagnetic isochrones can successfully fit the stars in the Rizzuto et al. sample with ages 1.6-2.4 Myr, without the need to invoke magnetic effects. An upper limit on the vertical field strength on the surfaces of the Rizzuto stars is found to be ∼300 G for the low-mass secondaries of FF Tau and HP Tau/G2 and ∼100 G for the other, more massive stars. The Taurus SFR is so large (extending over many square degrees in the sky) that magnetic conditions may plausibly differ from star to star.

Keywords: magnetic stars; stellar convective zones; stellar evolutionary models; stellar magnetic fields; pre-main sequence stars
A Number of nearby Moving Groups May Be Fragments of Dissolving Open Clusters

We propose that 14 co-moving groups of stars uncovered by Kounkel & Covey may be related to known nearby moving groups and bridge those and nearby open clusters with similar ages and space velocities. This indicates that known nearby moving groups may be spatially much more extended than previously thought, and some of them might be parts of tidal tails around the cores of known open clusters, reminiscent of those recently found around the Hyades and a handful of other nearby clusters. For example, we find that both the nearby Carina and Columba associations may be linked to Theia 208 from Kounkel & Covey and together form parts of a large tidal tail around the Platais 8 open cluster. The AB Doradus moving group and Theia 301 may form a trailing tidal tail behind the Pleiades open cluster, with hints of a possible leading tidal tail in Theia 369. Similarly, we find that IC 2391 and its tidal tails identified by Meingast et al. may be extended by the nearby Argus association and are possibly further extended by Theia 115. The nearby Octans and Octans-Near associations, as well as Theia 94 and 95, may form a large tidal tail leading the poorly studied Platais 5 open cluster candidate. While a preliminary analysis of Gaia color-magnitude sequences hint that these structures are plausibly related, more observational evidence is still required to corroborate their consistent ages and space velocities. These observations may change our current understanding of nearby moving groups and the different pathways through which they can form. While some moving groups may have formed loosely in extended star formation events with rich spatial structure, others may in fact correspond to the tidal tails of nearby open clusters.

Keywords: stellar associations; open star clusters; stellar kinematics
Hiding Signatures of Gravitational Instability in Protoplanetary Disks with Planets

We carry out three-dimensional smoothed particle hydrodynamics simulations to show that a migrating giant planet strongly suppresses the spiral structure in self-gravitating disks. We present mock Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations that show that in the absence of a planet, spiral arms due to gravitational instability are easily observed. Whereas in the presence of a giant planet, the spiral structures are suppressed by the migrating planet resulting in a largely axisymmetric disk with a ring and gap structure. Our modeling of the gas kinematics shows that the planet's presence could be inferred, for example, using optically thin 13C16O. Our results show that it is not necessary to limit the gas mass of disks by assuming high dust-to-gas mass ratios in order to explain a lack of spiral features that would otherwise be expected in high-mass disks.

Keywords: protoplanetary disks
The Physical Thickness of Stellar Disks to z ∼ 2

In local disk galaxies such as our Milky Way, older stars generally inhabit a thicker disk than their younger counterparts. Two competing models have attempted to explain this result: one in which stars first form in thin disks that gradually thicken with time through dynamical heating, and one in which stars form in thick disks at early times and in progressively thinner disks at later times. We use a direct measure of the thicknesses of stellar disks at high redshift to discriminate between these scenarios. Using legacy Hubble Space Telescope imaging from the CANDELS and GOODS surveys, we measure the rest-optical scale heights of 491 edge-on disk galaxies spanning 0.4 ≤ z ≤ 2.5. We measure a median intrinsic scale height for the full sample of 0.74 ± 0.03 kpc, with little redshift evolution of both the population median and scatter. The median is consistent with the thick disk of the Milky Way today (0.6-1.1 kpc), but it is smaller than the median scale height of local disks (~1.5 kpc) that are matched to our high-redshift sample by descendant mass. These findings indicate that, while (1) disks as thick as the Milky Way's thick disk were in place at early times, (2) to explain the full disk galaxy population today, the stellar disks in galaxies need to on average physically thicken after formation.

Keywords: galaxy evolution; scale height; disk galaxies; high-redshift galaxies
Ubiquitous Molecular Outflows in z > 4 Massive, Dusty Galaxies. I. Sample Overview and Clumpy Structure in Molecular Outflows on 500 pc Scales

Massive galaxy-scale outflows of gas are one of the most commonly invoked mechanisms to regulate the growth and evolution of galaxies throughout the universe. While the gas in outflows spans a large range of temperatures and densities, the cold molecular phase is of particular interest because molecular outflows may be capable of suppressing star formation in galaxies by removing the star-forming gas. We have conducted the first survey of molecular outflows at z > 4, targeting 11 strongly lensed dusty, star-forming galaxies (DSFGs) with high-resolution Atacama Large Millimeter/submillimeter Array observations of OH 119 μm absorption as an outflow tracer. In this first paper, we give an overview of the survey, focusing on the detection rate and structure of molecular outflows. We find unambiguous evidence for outflows in 8/11 galaxies (73%), more than tripling the number known at z > 4. This implies that molecular winds in z > 4 DSFGs must have both a near-unity occurrence rate and large opening angles to be detectable in absorption. Lensing reconstructions reveal that 500 pc scale clumpy structures in the outflows are common. The individual clumps are not directly resolved, but from optical depth arguments we expect that future observations will require 50-200 pc spatial resolution to resolve them. We do not detect high-velocity [C II] wings in any of the sources with clear OH outflows, indicating that [C II] is not a reliable tracer of molecular outflows. Our results represent a first step toward characterizing molecular outflows at z > 4 at the population level, demonstrating that large-scale outflows are ubiquitous among early massive, dusty galaxies.

Keywords: high-redshift galaxies; galactic winds; gravitational lensing; galaxy formation
Temperature and Metallicity Gradients in the Hot Gas Outflows of M82

We utilize deep Chandra X-ray Observatory imaging and spectra of M82, the prototype of a starbursting galaxy with a multiphase wind, to map the hot plasma properties along the minor axis of the galaxy. We extract spectra from 11 regions up to ±2.5 kpc from the starbursting midplane and model the data as a multitemperature, optically thin thermal plasma with contributions from a nonthermal (power-law) component and from charge exchange (CX). We examine the gradients in best-fit parameters, including the intrinsic column density, plasma temperature, metal abundances, and number density of the hot gas as a function of distance from the M82 nucleus. We find that the temperatures and number densities of the warm-hot and hot plasma peak at the starbursting ridge and decrease along the minor axis. The temperature and density profiles are inconsistent with spherical adiabatic expansion of a super-heated wind and suggest mass loading and mixing of the hot phase with colder material. Nonthermal emission is detected in all of the regions considered, and CX comprises 8%-25% of the total absorption-corrected, broadband (0.5-7 keV) X-ray flux. We show that the abundances of O, Ne, Mg, and Fe are roughly constant across the regions considered, while Si and S peak within 500 pc of the central starburst. These findings support a direct connection between the M82 superwind and the warm-hot, metal-rich circumgalactic medium (CGM).

Keywords: starburst galaxies; galactic winds
GOLDRUSH. IV. Luminosity Functions and Clustering Revealed with 4,000,000 Galaxies at z 2-7: Galaxy-AGN Transition, Star Formation Efficiency, and Implication for Evolution at z > 10

We present new measurements of rest-UV luminosity functions and angular correlation functions from 4,100,221 galaxies at z ~ 2-7 identified in the Subaru/Hyper Suprime-Cam survey and CFHT Large Area U-band Survey. The obtained luminosity functions at z ~ 4-7 cover a very wide UV luminosity range of ~ $0.002\mbox{--}2000{L}_{\mathrm{UV}}^{* }$ combined with previous studies, confirming that the dropout luminosity function is a superposition of the active galactic nucleus (AGN) luminosity function dominant at M UV ≲ -24 mag and the galaxy luminosity function dominant at M UV ≳ -22 mag, consistent with galaxy fractions based on 1037 spectroscopically identified sources. Galaxy luminosity functions estimated from the spectroscopic galaxy fractions show the bright-end excess beyond the Schechter function at ≳2σ levels, possibly made by inefficient mass quenching, low dust obscuration, and/or hidden AGN activity. By analyzing the correlation functions at z ~ 2-6 with HOD models, we find a weak redshift evolution (within 0.3 dex) of the ratio of the star formation rate (SFR) to the dark matter accretion rate, $\mathrm{SFR}/{\dot{M}}_{{\rm{h}}}$ , indicating the almost constant star formation efficiency at z ~ 2-6, as suggested by our earlier work at z ~ 4-7. Meanwhile, the ratio gradually increases with decreasing redshift at z < 5 within 0.3 dex, which quantitatively reproduces the cosmic SFR density evolution, suggesting that the redshift evolution is primarily driven by the increase of the halo number density due to the structure formation, and the decrease of the accretion rate due to the cosmic expansion. Extrapolating this calculation to higher redshifts assuming the constant efficiency suggests a rapid decrease of the SFR density at z > 10 with ∝ 10-0.5(1+z), which will be directly tested with the James Webb Space Telescope.

Keywords: galaxy evolution; galaxy formation; high-redshift galaxies
The JAGWAR Prowls LIGO/Virgo O3 Paper I: Radio Search of a Possible Multimessenger Counterpart of the Binary Black Hole Merger Candidate S191216ap

We present a sensitive search with the Karl G. Jansky Very Large Array for the radio counterpart of the gravitational wave candidate S191216ap, which is classified as a binary black hole merger and suggested to be a possible multimessenger event, based on the detection of a high-energy neutrino and a TeV photon. We carried out a blind search at C band (4-8 GHz) over 0.3 deg2 of the gamma-ray counterpart of S191216ap reported by the High-Altitude Water Cerenkov Observatory (HAWC). Our search, spanning three epochs over 130 days of postmerger and having a mean source-detection threshold of 75 μJy beam-1 (4σ), yielded five variable sources associated with active galactic nucleus activity and no definitive counterpart of S191216ap. We find <2% (3.0% ± 1.3%) of the persistent radio sources at 6 GHz to be variable on a timescale of <1 week (week-months), consistent with previous radio variability studies. Our 4σ radio luminosity upper limit of ∼1.2 × 1028 erg s-1 Hz-1 on the afterglow of S191216ap, within the HAWC error region, is 5-10 times deeper than previous binary black hole (BBH) radio afterglow searches. Comparing this upper limit with theoretical expectations given by Perna et al. for putative jets launched by BBH mergers, for on-axis jets with energy ≃1049 erg, we can rule out jet opening angles ≲ 20° (assuming that the counterpart lies within the 1σ HAWC region that we observed).

Keywords: surveys; catalogs; radio continuum emission
Alleviating the Need for Exponential Evolution of JWST Galaxies in 1010 M ⊙ Haloes at z > 10 by a Modified ΛCDM Power Spectrum

We infer the evolution of the UV luminosities of galaxies in haloes of masses 1010-1011 M ⊙ in the redshift range of z ~ 9-16 from the recent JWST data. Within the standard ΛCDM cosmological model, it is found that the average luminosities in this halo mass range show an exponential evolution with redshift, in excess of that expected from astrophysical considerations including the evolution of UV luminosity from Population III galaxies. We find that an enhancement of power on scales k ~ 1 Mpc-1, as captured by a cosmological transfer function modified from the ΛCDM form, is able to alleviate this effect and allow for a nonevolving UV luminosity as a function of redshift at z > 10, consistently with the corresponding findings for lower redshifts. We discuss the possible astrophysical and cosmological reasons for such an enhancement.

Keywords: cosmology; reionization; early universe; high-redshift galaxies
A Study on the X-Ray Pulse Profile and Spectrum of the Crab Pulsar Using NICER and Insight-HXMT's Observations

We analyze the energy dependence of the X-ray pulse profile and the phase-resolved spectra (PRS) of the Crab pulsar using observations from the Neutron star Interior Composition Explorer (NICER) and the Hard X-ray Modulation Telescope (Insight-HXMT). We parameterize the pulse profiles and quantify the evolution of these parameters in the broad energy band of 0.4-250 keV. A log-parabola function is used to fit the PRS in 2-250 keV, and the curvature of the spectrum, i.e., the evolution of the photon index with energy, as represented by the parameter β of the log-parabola model, also changes with phase. The relation of β and phase has two turning points slightly later than those of the pulse intensity profile, where the values of β are the lowest, suggesting that the energy-loss rate of the particles is the lowest in the corresponding regions. A three-segment broken-power-law model is also used to fit those PRS. The differences between the hard spectral index and the soft ones have a distribution similar to that of β, confirming the fitting results of the log-parabola model, while the broken energies are generally higher in the region bridging the two pulses. We find anticorrelations between the spectral indices and the curvature of the log-parabola model fitting and a similar anticorrelation between the spectral indices and broken energies of the broken-power-law model fitting, suggesting a scenario where the highest-energy particles are produced in regions where radiation energy loss is strongest.

Keywords: pulsars; x-ray stars
A New LBV Candidate in M33

The evolutionary relationships and mechanisms governing the behavior of the wide variety of luminous stars populating the upper H-R diagram are not well established. Luminous blue variables (LBVs) are particularly rare, with only a few dozen identified in the Milky Way and nearby galaxies. Since 2012, the Barber Observatory Luminous Stars Survey has monitored more than 100 luminous targets in M33, including M33C-4119 which has recently undergone photometric and spectroscopic changes consistent with an S Doradus eruption of an LBV.

Keywords: massive stars; triangulum galaxy; luminous blue variable stars
The Possibility of the Secondary Object in GW190814 as a Neutron Star

A compact object was observed with a mass of $2.50\mbox{--}2.67\,{M}_{\odot }$ by LIGO Scientific and Virgo collaborations (LVC) in GW190814, which provides a great challenge to investigations of supranuclear matter. To study this object, the properties of the neutron star are systematically calculated within the latest density-dependent relativistic mean-field (DDRMF) parameterizations, which are determined by the ground-state properties of spherical nuclei. The maximum masses of the neutron star calculated by DD-MEX and DD-LZ1 sets can be around $2.55\,{M}_{\odot }$ with quite stiff equations of state generated by their strong repulsive contributions from vector potentials at high densities. Their maximum speeds of sound cs/c are smaller than $\sqrt{0.8}$ at the center of the neutron star, and the dimensionless tidal deformabilities at $1.4\,{M}_{\odot }$ are less than 800. Furthermore, the radii of $1.4\,{M}_{\odot }$ also satisfy the constraint from the observation of simultaneous mass-radius measurements (Neutron star Interior Composition Explorer). Therefore, we conclude that one cannot exclude the possibility of the secondary object in GW190814 as a neutron star composed of hadron matter from DDRMF models.

Keywords: neutron stars; compact objects; nuclear astrophysics; gravitational wave astronomy
Does Metallicity Affect the Protoplanetary Disk Fraction? Answers from the Outer Milky Way

The role of metallicity in shaping protoplanetary disk evolution remains poorly comprehended. This study analyzes the disk fraction of 10 young (0.9–2.1 Myr) and low-metallicity (0.34–0.83 Z ⊙) clusters located in the outer Milky Way with Galactocentric distances between 10 and 13 kpc. Using JHK data obtained from UKIDSS, the calculated disk fraction values for low-mass stars (0.2–2 M ⊙) ranged from 42% to 7%. To enhance the statistical reliability of our analysis, eight additional low-metallicity clusters are sourced from previous studies with metallicity range 0.25–0.85 Z ⊙ along with our sample, resulting in a total of 18 regions with low metallicity. We find that low-metallicity clusters exhibit on average a 2.6 ± 0.2 times lower disk fraction compared to solar-metallicity clusters in all the age bins we have. Within the age range we can probe, our study does not find evidence of faster disk decay in subsolar-metallicity regions compared to solar-metallicity regions. Furthermore, we observe a positive correlation between cluster disk fraction and metallicity for two different age groups of 0.3–1.4 and 1.4–2.5 Myr. We emphasize that both cluster age and metallicity significantly affect the fraction of stars with evidence of inner disks.

Keywords: metallicity; protoplanetary disks; pre-main sequence; star formation
Effect of Dust in Circumgalactic Halos on the Cosmic Shear Power Spectrum

Weak gravitational lensing is a powerful statistical tool for probing the growth of cosmic structure and measuring cosmological parameters. However, as shown by studies such as by Ménard et al., dust in the circumgalactic region of halos dims and reddens background sources. In a weak lensing analysis, this selects against sources behind overdense regions; since there is more structure in overdense regions, we will underestimate the amplitude of density perturbations σ 8 if we do not correct for the effects of circumgalactic dust. To model the dust distribution we employ the halo model. Assuming a fiducial dust mass profile based on measurements from Ménard et al., we compute the ratio Z of the systematic error to the statistical error for a survey similar to the Nancy Grace Roman Space Telescope reference survey (2000 deg2 area, single-filter effective source density 30 galaxies arcmin-2). For a wave band centered at 1580 nm (H band), we find that Z H = 0.37. For a similar survey with wave band centered at 620 nm (r band), we also computed Z r = 2.8. Within our fiducial dust model, since Z r > 1, the systematic effect of dust will be significant on weak lensing image surveys. We also computed the dust bias on the amplitude of the power spectrum, σ 8, and found it to be for each wave band Δσ 8/σ 8 = -3.1 × 10-4 (H band) or -2.2 × 10-3 (r band) if all other parameters are held fixed (the forecast Roman statistical-only error σ(σ 8)/σ 8 is 9 × 10-4).

Keywords: large-scale structure of the universe
A Systematic Study about Orbit Flips of Test Particles Caused by Eccentric Von Zeipel-Lidov-Kozai Effects

The problem of orbit flips caused by eccentric von Zeipel-Lidov-Kozai effects is systematically investigated by means of three approaches, including Poincaré sections, dynamical system theory (periodic orbits and invariant manifolds), and perturbation treatments. Poincaré sections show that orbit flips are due to the existence of islands of libration centered at inclination of 90°, dynamical system theory shows that orbit flips are due to the existence of polar periodic orbits and invariant manifolds, and perturbative treatments indicate that orbit flips are due to the libration of a certain critical argument. Using these approaches, the boundaries of flipping regions in the entire parameter space are produced, and they are in excellent agreement with one another. Through analysis, the essence of flipping orbits is reached: (a) flipping orbits are a kind of quasiperiodic trajectory around polar periodic orbits and invariant manifolds at the same level of Hamiltonian provide boundaries of flipping regions, and (b) flipping orbits are a kind of resonant trajectory, and resonant width measures the size of flipping regions.

Keywords: celestial mechanics; three-body problem; perturbation methods; asteroid satellites; asteroid dynamics; orbital motion; orbital resonances; gravitational interaction
A Single-pulse Study of PSR J1022+1001 Using the FAST Radio Telescope

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we have recorded ∼105 single pulses from PSR J1022+1001. We studied the polarization properties, their energy distribution, and their times of arrival. This is only possible with the high sensitivity available using FAST. There is no indication that PSR J1022+1001 exhibits giant pulse, nulling, or traditional mode changing phenomena. The energy in the leading and trailing components of the integrated profile is shown to be correlated. The degree of both linear and circular polarization increases with the pulse flux density for individual pulses. Our data indicates that pulse jitter leads to an excess noise in the timing residuals of 67 ns when scaled to one hour, which is consistent with Liu et al. We have unsuccessfully trialed various methods to improve timing precision through the selection of specific single pulses. Our work demonstrates that FAST can detect individual pulses from pulsars that are observed in order to detect and study gravitational waves. This capability enables detailed studies, and parameterization, of the noise processes that affect the sensitivity of a pulsar timing array.

Keywords: pulsars; astronomy data analysis