adsabs/SciX_UAT_keywords huggingface dataset:
Neutral-charged-particle Collisions as the Mechanism for Accretion Disk Angular Momentum Transport

The matter in an accretion disk must lose angular momentum when moving radially inwards but how this works has long been a mystery. By calculating the trajectories of individual colliding neutrals, ions, and electrons in a weakly ionized 2D plasma containing gravitational and magnetic fields, we numerically simulate accretion disk dynamics at the particle level. As predicted by Lagrangian mechanics, the fundamental conserved global quantity is the total canonical angular momentum, not the ordinary angular momentum. When the Kepler angular velocity and the magnetic field have opposite polarity, collisions between neutrals and charged particles cause: (i) ions to move radially inwards, (ii) electrons to move radially outwards, (iii) neutrals to lose ordinary angular momentum, and (iv) charged particles to gain canonical angular momentum. Neutrals thus spiral inward due to their decrease of ordinary angular momentum while the accumulation of ions at small radius and accumulation of electrons at large radius produces a radially outward electric field. In 3D, this radial electric field would drive an out-of-plane poloidal current that produces the magnetic forces that drive bidirectional astrophysical jets. Because this neutral angular momentum loss depends only on neutrals colliding with charged particles, it should be ubiquitous. Quantitative scaling of the model using plausible disk density, temperature, and magnetic field strength gives an accretion rate of 3 × 10-8 solar mass per year, which is in good agreement with observed accretion rates.

Keywords: accretion; stellar accretion; jets; plasma jets; protoplanetary disks; circumstellar disks; plasma astrophysics
Radio Signature of a Distant behind-the-limb CME on 2017 September 6

We discuss properties of a Type IV burst, which was observed on 2017 September 6, as a result of the powerful flare X 9.3. At decameter wavelengths this burst was observed by the radio telescopes STEREO A, URAN-2, and the Nancay Decameter Array at frequencies 5-35 MHz. This moving Type IV burst was associated with a coronal mass ejection (CME) propagating in the southwest direction with a speed of 1570 km s-1. The maximum radio flux of this burst was about 300 s.f.u. and the polarization was more than 40%. In the frequency range of 8-33 MHz it continued for more than 2 hr. For STEREO A the associated CME was behind the limb, and its longitudinal angle was about 160°. This moving Type IV burst was observed by STEREO A at frequencies of 5-15 MHz in spite of the low sensitivity of STEREO A. This means that the radio emission directivity of a Type IV burst is rather wide. Assuming the plasma mechanism of Type IV radio emission we derived the plasma density distribution in the CME core at distances of 5.6 Rs and 9.8 Rs (Rs is the solar radius), and its mass to be about 1016 g. It is planned that the minimum perihelion of the Parker Solar Probe (PSP) spacecraft will be at about 9 Rs. So we discuss in what conditions PSP will be in if it crosses a similar CME core.

Keywords: solar coronal mass ejections; radio bursts; solar radio emission; radio telescopes
The X-SHOOTER/ALMA Sample of Quasars in the Epoch of Reionization. I. NIR Spectral Modeling, Iron Enrichment, and Broad Emission Line Properties

We present X-SHOOTER near-IR spectroscopy of a large sample of 38 luminous (M1450 = -29.0 to -24.4) quasars at 5.78 < z < 7.54, which have complementary [C II]158μm observations from ALMA. This X-SHOOTER/ALMA sample provides us with the most comprehensive view of reionization-era quasars to date, allowing us to connect the quasar properties with those of its host galaxy. In this work we introduce the sample, discuss data reduction and spectral fitting, and present an analysis of the broad emission line properties. The measured Fe II/Mg II flux ratio suggests that the broad-line regions of all quasars in the sample are already enriched in iron. We also find the Mg II line to be on average blueshifted with respect to the [C II] redshift with a median of -391 km s-1. A significant correlation between the Mg II-[C II]158μm and C IV-[C II]158μm velocity shifts indicates a common physical origin. Furthermore, we fRequently detect large C IV-Mg II emission line velocity blueshifts in our sample with a median value of -1848 km s-1. While we find all other broad emission line properties not to be evolving with redshift, the median C IV-Mg II blueshift is much larger than found in low-redshift, luminosity-matched quasars (-800 km s-1). Dividing our sample into two redshift bins, we confirm an increase of the average C IV-Mg II blueshift with increasing redshift. Future observations of the rest-frame optical spectrum with the James Webb Space Telescope will be instrumental in further constraining the possible evolution of quasar properties in the epoch of reionization.

Keywords: reionization; supermassive black holes; quasars; active galaxies; active galactic nuclei; early universe
The Mass Function of Supermassive Black Holes in the Direct Collapse Scenario

One of the ideas to explain the existence of supermassive black holes (SMBH) in place by z ∼ 7 is a phase of rapid accretion onto direct collapse black holes (DCBH) that started their lives with masses ∼104-5 ${M}_{\odot }$ . Considering the DCBH scenario, we show that the SMBH mass function has two characteristic features: 1. a power-law at intermediate masses whose index is the dimensionless ratio α ≡ λ/γ, where λ is the growth rate of the number of DCBH and γ is the growth rate of DCBH masses, both during the DCBH growth era; 2. a break in the power law profile set by β ≡ γ T, where T is the duration of the DCBH growth era. The observed quasar luminosity function can be described with this tapered power-law function.

Keywords: supermassive black holes; quasars
How Large Is a Disk-What Do Protoplanetary Disk Gas Sizes Really Mean?

It remains unclear what mechanism is driving the evolution of protoplanetary disks. Direct detection of the main candidates, either turbulence driven by magnetorotational instabilities or magnetohydrodynamical disk winds, has proven difficult, leaving the time evolution of the disk size as one of the most promising observables able to differentiate between these two mechanisms. But to do so successfully, we need to understand what the observed gas disk size actually traces. We studied the relation between R CO,90%, the radius that encloses 90% of the 12CO flux, and R c , the radius that encodes the physical disk size, in order to provide simple prescriptions for conversions between these two sizes. For an extensive grid of thermochemical models, we calculate R CO,90% from synthetic observations and relate properties measured at this radius, such as the gas column density, to bulk disk properties, such as R c and the disk mass M disk. We found an empirical correlation between the gas column density at R CO,90% and disk mass: ${N}_{\mathrm{gas}}{({R}_{\mathrm{CO},90 \% })\approx 3.73\,\times \,{10}^{21}({M}_{\mathrm{disk}}/{M}_{\odot })}^{0.34}\ {\mathrm{cm}}^{-2}$ . Using this correlation we derive an analytical prescription of R CO,90% that only depends on R c and M disk. We derive R c for disks in Lupus, Upper Sco, Taurus, and the DSHARP sample, finding that disks in the older Upper Sco region are significantly smaller (<R c > = 4.8 au) than disks in the younger Lupus and Taurus regions (<R c > = 19.8 and 20.9 au, respectively). This temporal decrease in R c goes against predictions of both viscous and wind-driven evolution, but could be a sign of significant external photoevaporation truncating disks in Upper Sco.

Keywords: protoplanetary disks; astrochemistry
PHANGS-JWST First Results: Multiwavelength View of Feedback-driven Bubbles (the Phantom Voids) across NGC 628

We present a high-resolution view of bubbles within the Phantom Galaxy (NGC 628), a nearby (~10 Mpc), star-forming (~2 M ⊙ yr-1), face-on (i ~ 9°) grand-design spiral galaxy. With new data obtained as part of the Physics at High Angular resolution in Nearby GalaxieS (PHANGS)-JWST treasury program, we perform a detailed case study of two regions of interest, one of which contains the largest and most prominent bubble in the galaxy (the Phantom Void, over 1 kpc in diameter), and the other being a smaller region that may be the precursor to such a large bubble (the Precursor Phantom Void). When comparing to matched-resolution Hα observations from the Hubble Space Telescope, we see that the ionized gas is brightest in the shells of both bubbles, and is coincident with the youngest (~1 Myr) and most massive (~105 M ⊙) stellar associations. We also find an older generation (~20 Myr) of stellar associations is present within the bubble of the Phantom Void. From our kinematic analysis of the H I, H2 (CO), and H II gas across the Phantom Void, we infer a high expansion speed of around 15 to 50 km s-1. The large size and high expansion speed of the Phantom Void suggest that the driving mechanism is sustained stellar feedback due to multiple mechanisms, where early feedback first cleared a bubble (as we observe now in the Precursor Phantom Void), and since then supernovae have been exploding within the cavity and have accelerated the shell. Finally, comparison to simulations shows a striking resemblance to our JWST observations, and suggests that such large-scale, stellar-feedback-driven bubbles should be common within other galaxies.

Keywords: superbubbles; stellar feedback; interstellar medium; infrared astronomy
Age Determination of LAMOST Red Giant Branch Stars Based on the Gradient Boosting Decision Tree Method

In this study, we estimate the stellar ages of LAMOST DR8 red giant branch (RGB) stars based on the gradient boosting decision tree (GBDT) algorithm. We used 2643 RGB stars extracted from the APOKASC-2 asteroseismological catalog as the training data set. After selecting the parameters ([α/Fe], [C/Fe], T eff, [N/Fe], [C/H], log g) highly correlated with age using GBDT, we apply the same GBDT method to the new catalog of more than 590,000 stars classified as RGB stars. The test data set shows that the median relative error is around 11.6% for the method. We also compare the predicted ages of RGB stars with other studies (e.g., based on APOGEE) and find some systematic differences. The final uncertainty is about 15%–30% compared to the ages of open clusters. Then, we present the spatial distribution of the RGB sample with an age determination, which could recreate the expected result, and discuss systematic biases. All these diagnostics show that one can apply the GBDT method to other stellar samples to estimate atmospheric parameters and age.

Keywords: milky way disk; stellar ages; red giant branch; catalogs
The Effect of the Velocity Distribution on Kilonova Emission

The electromagnetic emission from the nonrelativistic ejecta launched in neutron star mergers (either dynamically or through a disk wind) has the potential to probe both the total mass and composition of this ejecta. These observations are crucial in understanding the role of these mergers in the production of r-process elements in the Universe. However, many properties of the ejecta can alter the light curves and we must both identify which properties play a role in shaping this emission and understand the effects these properties have on the emission before we can use observations to place strong constraints on the amount of r-process elements produced in the merger. This paper focuses on understanding the effect of the velocity distribution (amount of mass moving at different velocities) for lanthanide-rich ejecta on the light curves and spectra. The simulations use distributions guided by recent calculations of disk outflows and compare the velocity-distribution effects to those of ejecta mass, velocity, and composition. Our comparisons show that uncertainties in the velocity distribution can lead to a factor of 2-4 uncertainties in the inferred ejecta mass based on peak infrared luminosities. We also show that early-time UV or optical observations may be able to constrain the velocity distribution, reducing the uncertainty in the ejecta mass.

Keywords: neutron stars; gravitational wave sources; transient sources; ultraviolet transient sources
The Merger Dynamics of the Galaxy Cluster A1775: New Insights from Chandra and XMM-Newton for a Cluster Simultaneously Hosting a Wide-angle Tail and a Narrow-angle Tail Radio Source

We present a new study of the merger dynamics of A1775 by analyzing the high-quality Chandra and XMM-Newton archival data. We confirm/identify an arc-shaped edge (i.e., the head) at ∼48 kpc west of the X-ray peak, a split cold gas tail that extends eastward to ∼163 kpc, and a plume of spiral-like X-ray excess (within about 81-324 kpc northeast of the cluster core) that connects to the end of the tail. The head, across which the projected gas temperature rises outward from ${3.39}_{-0.18}^{+0.28}$ to ${5.30}_{-0.43}^{+0.54}$ keV, is found to be a cold front with a Mach number of ${ \mathcal M }\sim 0.79$ . Along the surfaces of the cold front and tail, typical Kelvin-Helmholtz instability features (noses and wings, etc.) are found and are used to constrain the upper limit of the magnetic field (∼11.2 μG) and the viscosity suppression factor (∼0.01). Combining optical and radio evidence, we propose a two-body merger (instead of systematic motion in a large-scale gas environment) scenario and have carried out idealized hydrodynamic simulations to verify it. We find that the observed X-ray emission and temperature distributions can be best reproduced with a merger mass ratio of 5 after the first pericentric passage. The NAT radio galaxy is thus more likely to be a single galaxy falling into the cluster center at a relative velocity of 2800 km s-1, a speed constrained by its radio morphology. The infalling subcluster is expected to have a relatively low gas content, because only a gas-poor subcluster can cause central-only disturbances as observed in such an off-axis merger.

Keywords: galaxy clusters; intracluster medium; radio galaxies; hydrodynamical simulations
Wide Binaries with White Dwarf or Neutron Star Companions Discovered from Gaia DR3 and LAMOST

The Gaia Data Release 3 (DR3) mission has identified and provided about 440,000 binary systems with orbital solutions, offering a valuable resource for searching binaries including a compact component. By combining the Gaia DR3 data with radial velocities from the LAMOST spectroscopic survey, we identify three wide binaries possibly containing a compact object. For two of these sources with a main-sequence companion, no obvious excess is observed in the blue/red band of the Gaia DR3 XP spectra, and the LAMOST medium-resolution spectra exhibit clear single-lined features. The absence of an additional component from spectral disentangling analysis further suggests the presence of compact objects within these systems. On the other hand, the visible star of the third source is a stripped giant star. In contrast to most binaries including stripped stars, no emission line is detected in the optical spectra. The unseen star could potentially be a massive white dwarf or neutron star, but the possibility of an F-type dwarf star scenario cannot be ruled out. An examination of about 10 binaries containing white dwarfs or neutron stars using both kinematic and chemical methods suggests most of these systems are located in the thin disk of the Milky Way.

Keywords: binary stars; white dwarf stars; neutron stars
Solar-like Dynamos and Rotational Scaling of Cycles from Star-in-a-box Simulations

Magnetohydrodynamic star-in-a-box simulations of convection and dynamos in a solar-like star with different rotation rates are presented. These simulations produce solar-like differential rotation with a fast equator and slow poles and magnetic activity that resembles that of the Sun with equatorward migrating activity at the surface. Furthermore, the ratio of rotation to cycle period is almost constant, as the rotation period decreases in the limited sample considered here. This is reminiscent of the suggested inactive branch of stars from observations and differs from most earlier simulation results from spherical shell models. While the exact excitation mechanism of the dynamos in the current simulations is not yet clear, it is shown that it is plausible that the greater freedom that the magnetic field has due to the inclusion of the radiative core and regions exterior to the star are important in shaping the dynamo.

Keywords: stellar magnetic fields; magnetohydrodynamical simulations; astrophysical fluid dynamics
Precise Positions of Five Major Uranian Satellites During 2008-2014 Based on Gaia EDR3

The five major Uranian satellites (Ariel, Umbriel, Titania, Oberon, and Miranda) were observed by a 1.56 m telescope at Sheshan Station of Shanghai Astronomical Observatory during 2008-2014 and a total of 1915 positions of these five satellites were presented in this paper. Since all five satellites are close to Uranus, their positions are affected by the uneven background, which is caused by the halo of Uranus. The median filtering method is used to remove the influence of the halo of the bright Uranus, which also made the rate of target detection increase by 30%-100%, especially for Miranda. Gaia EDR3 is used as the reference catalog when calculating positions of the five satellites. A comparison between our positions with the theoretical positions of the satellites from IMCCE is given. Such precise positions over a long time will be very helpful to improve the orbit parameters of the five major Uranian satellites. * Released on 2021 March 1st.

Keywords: uranian satellites
Implicit Likelihood Inference of Reionization Parameters from the 21 cm Power Spectrum

The first measurements of the 21 cm brightness temperature power spectrum from the epoch of reionization will very likely be achieved in the near future by radio interferometric array experiments such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA). Standard MCMC analyses use an explicit likelihood approximation to infer the reionization parameters from the 21 cm power spectrum. In this paper, we present a new Bayesian inference of the reionization parameters where the likelihood is implicitly defined through forward simulations using density estimation likelihood-free inference (DELFI). Realistic effects, including thermal noise and foreground avoidance, are also applied to the mock observations from the HERA and SKA. We demonstrate that this method recovers accurate posterior distributions for the reionization parameters, and it outperforms the standard MCMC analysis in terms of the location and size of credible parameter regions. With the minute-level processing time once the network is trained, this technique is a promising approach for the scientific interpretation of future 21 cm power spectrum observation data. Our code 21cmDELFI-PS is publicly available at this link (https://github.com/Xiaosheng-Zhao/21cmDELFI).

Keywords: h i line emission; astrostatistics; bayesian statistics; neural networks; reionization
Virgo Filaments. II. Catalog and First Results on the Effect of Filaments on Galaxy Properties

Virgo is the nearest galaxy cluster; it is thus ideal for studies of galaxy evolution in dense environments in the local universe. It is embedded in a complex filamentary network of galaxies and groups, which represents the skeleton of the large-scale Laniakea supercluster. Here we assemble a comprehensive catalog of galaxies extending up to ~12 virial radii in projection from Virgo to revisit the cosmic-web structure around it. This work is the foundation of a series of papers that will investigate the multiwavelength properties of galaxies in the cosmic web around Virgo. We match spectroscopically confirmed sources from several databases and surveys including HyperLeda, NASA Sloan Atlas, NASA/IPAC Extragalactic Database, and ALFALFA. The sample consists of ~7000 galaxies. By exploiting a tomographic approach, we identify 13 filaments, spanning several megaparsecs in length. Long >17 h -1 Mpc filaments, tend to be thin (<1 h -1 Mpc in radius) and with a low-density contrast (<5), while shorter filaments show a larger scatter in their structural properties. Overall, we find that filaments are a transitioning environment between the field and cluster in terms of local densities, galaxy morphologies, and fraction of barred galaxies. Denser filaments have a higher fraction of early-type galaxies, suggesting that the morphology-density relation is already in place in the filaments, before galaxies fall into the cluster itself. We release the full catalog of galaxies around Virgo and their associated properties.

Keywords: galaxy clusters; virgo cluster; large-scale structure of the universe; astronomy databases; catalogs; surveys
Very Large Array Multiband Radio Imaging of the Triple AGN Candidate SDSS J0849+1114

Kiloparsec-scale triple active galactic nuclei (AGNs), potential precursors of gravitationally bound triple massive black holes (MBHs), are rarely seen objects and believed to play an important role in the evolution of MBHs and their host galaxies. In this work we present a multiband (3.0, 6.0, 10.0, and 15.0 GHz), high-resolution radio imaging of the triple AGN candidate, SDSS J0849+1114, using the Very Large Array. Two of the three nuclei (A and C) are detected at 3.0, 6.0, and 15 GHz for the first time, both exhibiting a steep spectrum over 3-15 GHz (with a spectral index -0.90 ± 0.05 and -1.03 ± 0.04) consistent with a synchrotron origin. Nucleus A, the strongest nucleus among the three, shows a double-sided jet, with the jet orientation changing by ~20° between its inner 1″ and the outer 5.″5 (8.1 kpc) components, which may be explained as the MBH's angular momentum having been altered by merger-enhanced accretion. Nucleus C also shows a two-sided jet, with the western jet inflating into a radio lobe with an extent of 1.″5 (2.2 kpc). The internal energy of the radio lobe is estimated to be 5.0 × 1055 erg, for an equipartition magnetic field strength of ~160 μG. No significant radio emission is detected at all four frequencies for nucleus B, yielding an upper limit of 15, 15, 15, and 18 μJy beam-1 at 3.0, 6.0, 10.0, and 15.0 GHz, based on which we constrain the star formation rate in nucleus B to be ≲0.4 M ⊙ yr-1.

Keywords: active galaxies; galaxy interactions; galaxy nuclei; radio continuum emission
Establishing Earth's Minimoon Population through Characterization of Asteroid 2020 CD3

We report on our detailed characterization of Earth's second known temporary natural satellite, or minimoon, asteroid 2020 CD3. An artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the S or V complex in asteroid taxonomy. The discovery of 2020 CD3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. The estimated diameter of ${1.2}_{-0.2}^{+0.4}$ m and geocentric capture approximately a decade after the first known minimoon, 2006 RH120, are in agreement with theoretical predictions. The capture duration of 2020 CD3 of at least 2.7 yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020 CD3's atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. More discoveries and a detailed characterization of the population can be expected with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.

Keywords: near-earth objects; asteroids; transient sources; astrometry; broad band photometry; earth-moon system; light curves; orbit determination