adsabs/SciX_UAT_keywords huggingface dataset:
'Oumuamua's Rotation with the Mechanical Torque Produced by Interstellar Medium

The first interstellar object 'Oumuamua was discovered in 2017. When 'Oumuamua travels in interstellar space, it keeps colliding with the interstellar medium (ISM). Given a sufficiently long interaction time, its rotation state may change significantly because of the angular momentum transfer with the interstellar medium. Using generated Gaussian random spheres with dimension ratios 6:1:1 and 5:5:1, this paper explores the ISM torque curve and proposes that ISM collision may account for 'Oumuamua's tumbling with the simple constant-torque analytical method. The statistic results show that the asymptotic obliquities distribute mostly at 0° and 180° and most cases spin down at the asymptotic obliquity, indicating that the ISM collision effect is similar to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect with zero heat conductivity assumed. Given a long time of deceleration of the spin rate, an initial major-axis rotation may evolve into tumbling motion under ISM torque. Using a constant-torque analytical model, the timescales of evolving into tumbling for the sample of 200 shapes are found to range from several gigayears to tens of gigayears, highly dependent on the chosen shape. The mean value is about 8.5 ± 0.5 Gyr for prolate shapes and 7.3 ± 0.4 Gyr for oblate shapes. Rotation of asteroids in the Oort cloud might also be dominated by the ISM collision effect since the YORP effect is quite weak at such a long distance from the Sun. Although this paper assumes an ideal mirror reflection and a constant relative velocity of 'Oumuamua, the results still show the importance of the ISM collision effect.

Keywords: asteroids; diffuse interstellar clouds; oort cloud objects
Black Hole Polarimetry I. A Signature of Electromagnetic Energy Extraction

In 1977, Blandford and Znajek showed that the electromagnetic field surrounding a rotating black hole can harvest its spin energy and use it to power a collimated astrophysical jet, such as the one launched from the center of the elliptical galaxy M87. Today, interferometric observations with the Event Horizon Telescope (EHT) are delivering high-resolution, event-horizon-scale, polarimetric images of the supermassive black hole M87* at the jet launching point. These polarimetric images offer an unprecedented window into the electromagnetic field structure around a black hole. In this paper, we show that a simple polarimetric observable-the phase ∠β 2 of the second azimuthal Fourier mode of the linear polarization in a near-horizon image-depends on the sign of the electromagnetic energy flux and therefore provides a direct probe of black hole energy extraction. In Boyer-Lindquist coordinates, the Poynting flux for axisymmetric electromagnetic fields is proportional to the product B ϕ B r . The phase ∠β 2 likewise depends on the ratio B ϕ /B r , thereby enabling an observer to determine the direction of electromagnetic energy flow in the near-horizon environment experimentally. Data from the 2017 EHT observations of M87* are consistent with electromagnetic energy outflow. Currently envisioned multifrequency observations of M87* will achieve higher dynamic range and angular resolution, and hence deliver measurements of ∠β 2 closer to the event horizon as well as better constraints on Faraday rotation. Such observations will enable a definitive test for energy extraction from the black hole M87*.

Keywords: black holes; relativistic jets; accretion; very long baseline interferometry; magnetohydrodynamics; supermassive black holes; magnetohydrodynamical simulations; event horizons; black hole physics
Can the Parker Solar Probe Detect a CME-flare Current Sheet?

A current sheet (CS) is the central structure in the disrupting magnetic configuration during solar eruptions. More than 90% of the free magnetic energy (the difference between the energy in the nonpotential magnetic field and that in the potential one) stored in the coronal magnetic field beforehand is converted into the heating and kinetic energy of the plasma, as well as accelerating charged particles, by magnetic reconnection occurring in the CS. However, the detailed physical properties and fine structures of the CS are still unknown, since there is no relevant information obtained via in situ detections. The Parker Solar Probe (PSP) may provide us with such information should it traverse a CS in an eruption. The perihelion of PSP's final orbit is located at about 10 solar radii from the center of the Sun, so it can observe the CS at a very close distance, or even traverse the CS, which would provide us with a unique opportunity to look into the fine properties and structures of the CS, helping to reveal the detailed physics of large-scale reconnection that would have been impossible before. We evaluate the probability that PSP can traverse a CS, and examine the orbit of a PSP-like spacecraft that has the highest probability to traverse a CS.

Keywords: solar coronal mass ejections; solar magnetic reconnection; heliocentric orbit
A Theoretical Framework for the Mass Distribution of Gas Giant Planets Forming through the Core Accretion Paradigm

This paper constructs a theoretical framework for calculating the distribution of masses for gas giant planets forming via the core accretion paradigm. Starting with known properties of circumstellar disks, we present models for the planetary mass distribution over the range 0.1MJ ≤ Mp < 10MJ. If the circumstellar disk lifetime is solely responsible for the end of planetary mass accretion, the observed (nearly) exponential distribution of disk lifetime would imprint an exponential falloff in the planetary mass function. This result is in apparent conflict with observations, which suggest that the mass distribution has a (nearly) power-law form of ${dF}/{{dM}}_{{\rm{p}}}\sim {M}_{{\rm{p}}}^{-p}$ , with an index of p ≈ 1.3, over the relevant planetary mass range (and for stellar masses ∼0.5-2M⊙). The mass accretion rate onto the planet depends on the fraction of the (circumstellar) disk accretion flow that enters the Hill sphere, and on the efficiency with which the planet captures the incoming material. Models for the planetary mass function that include distributions for these efficiencies, with uninformed priors, can produce nearly power-law behavior, consistent with current observations. The disk lifetimes, accretion rates, and other input parameters depend on the mass of the host star. We show how these variations lead to different forms for the planetary mass function for different stellar masses. Compared to stars with masses M* = 0.5-2M⊙, stars with smaller masses are predicted to have a steeper planetary mass function (fewer large planets).

Keywords: exoplanet formation; exoplanet astronomy
Constraining the Venus Interior Structure with Future VERITAS Measurements of the Gravitational Atmospheric Loading

The complex dynamics of the Venus atmosphere produces a periodic mass redistribution pattern that creates a time-variable modulation of the gravity field of Venus. This gravity signal depends on the net transport of mass across the globe and on the response of the solid body to the normal loading of its crust imparted by the atmosphere. In this work, we explore the possibility of measuring this phenomenon with VERITAS, a NASA Discovery-class mission. By simulating the gravity science experiment, we explore the possibility of measuring the response of Venus to the atmospheric loading, parametrized by the loading Love numbers ( ${k}_{l}^{{\prime} }$ ), and assess the dependence of these parameters on fundamental interior structure properties. Using the most recent models of Venus' interior, we compute the Venus Love numbers in a compressible viscoelastic setting and compare them with the predicted uncertainty of the VERITAS measurements. We show that VERITAS will measure ${k}_{2}^{{\prime} }$ at the 4% level and that this measurement could possibly help to distinguish between different equally plausible interior structure models, especially allowing us to distinguish different rheological laws. We also show that a measurement campaign such as the VERITAS gravity science investigation has the potential of measuring ${k}_{2}^{{\prime} }$ not only at the loading forcing frequency, but also at the tidal frequency, ultimately providing a way to probe the response of the planet at different forcing periods.

Keywords: atmospheric tides; venus; orbit determination; planetary interior; planetary probes; planetary dynamics; planetary science
Nature of Supersonic Turbulence and Density Distribution Function in the Multiphase Interstellar Medium

Supersonic flows in the interstellar medium (ISM) are believed to be a key driver of the molecular cloud formation and evolution. Among molecular clouds' properties, the ratio between the solenoidal and compressive modes of turbulence plays important roles in determining the star formation efficiency. We use numerical simulations of supersonic converging flows of the warm neutral medium (WNM) resolving the thermal instability to calculate the early phase of molecular cloud formation, and we investigate the turbulence structure and the density probability distribution function (density PDF) of the multiphase ISM. We find that both the solenoidal and compressive modes have their power spectrum similar to the Kolmogorov spectrum. The solenoidal (compressive) modes account for ≳80% (≲20%) of the total turbulence power. When we consider both the cold neutral medium (CNM) and the thermally unstable neutral medium (UNM) up to T ≲ 400 K, the density PDF follows the lognormal distribution, whose width ${\sigma }_{s}^{}$ is well explained by the known relation from the isothermal turbulence as ${\sigma }_{s}^{}=\mathrm{ln}(1\,+{b}^{2}{{ \mathcal M }}^{2})$ (where b is the parameter representing the turbulence mode ratio and ${ \mathcal M }$ is the turbulent Mach number). The density PDF of the CNM component alone (T ≤ 50 K), however, exhibits a narrower ${\sigma }_{s}^{}$ by a factor of ~2. These results suggest that observational estimations of b based on the CNM density PDF requires the internal turbulence within each CNM clump but not the interclump relative velocity, the latter of which is instead powered by the WNM/UNM turbulence.

Keywords: interstellar medium; warm neutral medium; cold neutral medium; interstellar dynamics
Radio Emission of Nearby Early-type Galaxies in the Low and Very Low Radio Luminosity Range

We analyze radio continuum emission of early-type galaxies with dynamical measurements of central supermassive black hole (SMBH) masses and well-characterized large-scale environments, but regardless of the exact level of the nuclear activity. The 1.4 GHz radio fluxes collected with ~arcmin resolution for 62 nearby targets (distances ≲153 Mpc) correspond to low and very low monochromatic luminosities of L r ~ 1035-1041 erg s-1. We quantify possible correlations between the radio properties with the main parameters of SMBHs, host galaxies, and hot gaseous halos, finding a general bimodality in the radio luminosity distribution, with the borderline between radio-bright and radio-dim populations at $\mathrm{log}{L}_{{\rm{r}}}/{L}_{\mathrm{Edd}}\simeq -8.5$ . We analyze the far-infrared data for the targets, finding that all radio-bright and over a half of the radio-dim sources are overluminous in radio wavelengths with respect to the far-infrared-radio correlation. High-resolution radio maps reveal that the overwhelming majority of radio-dim sources is unresolved on the arcsecond scale, while the bulk of radio-bright sources display extended jets and lobes of low- and intermediate-power radio galaxies; these jets dominate the radio emission of radio-bright objects. Regarding the origin of the radio emission of radio-dim sources, we discuss two main possibilities. One possibility is the advection-dominated accretion flow model, in which the radio and nuclear X-ray radiative outputs at very low accretion rates are both dominated by unresolved jets. The other possibility is that the radio-dim sources, unlike the radio-bright ones, are characterized by low values of SMBH spins, so that their radio emission is not related to the jets, but instead is due to a combination of star-forming processes and previous nuclear outbursts.

Keywords: radio active galactic nuclei; radio galaxies; radio cores; early-type galaxies; radio jets
Multiple Stellar Populations of Globular Clusters from Homogeneous Ca-CN-CH-NH Photometry. VII. Metal-poor Populations in 47 Tucanae (NGC 104)

We present new large field-of-view (~1°×1°) Ca-CN photometry of the prototypical metal-rich globular cluster 47 Tucanae (NGC 104). Our results are the following. (1) The populational number ratios of the red giant branch (RGB) and red horizontal branch (RHB) are in excellent agreement: n(CN-w):n(CN-s) = 30:70 (±1-2), where the CN-w and CN-s stand for the CN-weak and CN-strong populations, respectively. Both the CN-s RGB and RHB populations are more centrally concentrated than those of CN-w populations are. (2) Our photometric metallicities of individual RGB stars in each population can be well described by bimodal distributions with two metallicity peaks, [Fe/H] ~-0.72 and -0.92 dex, where the metal-poor components occupy ~13% of the total RGB stars. The metal-poor populations are more significantly centrally concentrated than the metal-rich populations, showing a similar result that we found in M3. (3) The RGB bump V magnitudes of individual populations indicate that there is no difference in the helium abundance between the two metal-poor populations, while the helium enhancement of ΔY ~0.02-0.03 is required between the the two metal-rich populations. (4) The RHB morphology of 47 Tuc appears to support our idea of the bimodal metallicity distribution of the cluster. We suggest that 47 Tuc could be another example of merger remnants of two globular clusters, similar to M3 and M22. * Based on observations made with the Cerro Tololo Inter-American Observatory (CTIO) 1 m telescope, which is operated by the SMARTS consortium. †This work presents results from the European Space Agency space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement. The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia.

Keywords: stellar populations; population ii stars; hertzsprung russell diagram; globular star clusters; chemical abundances; stellar evolution; red giant branch; red giant bump; horizontal branch stars
Merging Things Together: Merger Pair Analysis from the IllustrisTNG Simulation Suite

Expanding on the work of Snyder et al., we present merger pair analysis of mock surveys from the IllustrisTNG suite of 3D cosmological simulations. Our results, shown in the context of previous work with Illustris-1, are consistent with a flattening of the pair fraction curve at a redshift of z = 2.

Keywords: galaxy mergers; extragalactic astronomy; astronomical simulations
Accretion-driven Sources in Spatially Resolved Lyα Emitters

Lyα emission is a standard tracer of starburst galaxies at high redshift. However, a number of local Lyα emitters (LAEs) are X-ray sources, suggesting a possible origin of Lyα photons other than young, hot stars, and which may be active at much later ages relative to the parent starburst. Resolved, nearby LAEs offer the opportunity to discriminate between diffuse X-ray emission arising from supernova-heated gas, high-mass X-ray binaries (HMXBs), or low-luminosity active galactic nuclei (LLAGN). We examine archival X-ray imaging from Chandra and XMM-Newton for 11 galaxies with spatially resolved Lyα imaging to determine the luminosity, morphology, and spectral hardness of the X-ray sources. The data are consistent with 9 of the 12, bright Lyα sources being driven by luminous, > ${10}^{40}\ \mathrm{erg}\ {{\rm{s}}}^{-1}$ X-ray sources. Half of the eight Chandra sources are unresolved. The data suggest that nuclear activity, whether from LLAGN or nuclear starbursts, may play an important role in Lyα emission. Our results also suggest a significant link between Lyα emission and HMXBs, ultraluminous X-ray sources, and/or LLAGN, which would imply that Lyα may be generated over timescales 1-2 orders of magnitude longer than produced by photoionization from OB stars. This highlights a critical need to quantify the relative contributions of different sources across cosmic time, to interpret Lyα observations and the resulting properties of distant galaxies.

Keywords: ultraviolet sources; extragalactic astronomy; high energy astrophysics; starburst galaxies; emission line galaxies; lyman-alpha galaxies; low-luminosity active galactic nuclei; x-ray active galactic nuclei
Exploration of Icy Ocean Worlds Using Geophysical Approaches

Geophysics-focused missions and improved geophysical data sets are critical for the future exploration of icy ocean worlds. Of particular interest is the exploration of the Galilean moon, Europa, and the Saturnian moons, Titan and Enceladus. These bodies likely have geologically active surfaces and may harbor habitable subsurface environments. Placing any candidate signatures for life in context requires further knowledge of the interior of these worlds. While the surfaces of these bodies have been mapped, their interiors remain poorly understood. Geophysical approaches such as geodesy, seismology, ice-penetrating radar and altimetry measurements, and electromagnetometry would provide critical information regarding the interior of these icy ocean worlds. The approaches described below would answer key science questions regarding ice shell and ocean dynamics, internal structure and interior layer thicknesses, near-surface structure, and how material from the deep interior might be exchanged with the surface. Here we outline the geophysical environments of Enceladus, Europa, and Titan; some outstanding science questions that remain to be addressed; and examples of the geophysical approaches that can provide the context to better understand icy ocean worlds.

Keywords: geodesics; magnetohydrodynamics; lunar seismology; galilean satellites; saturnian satellites; ocean planets
Role of Small-scale Impulsive Events in Heating the X-Ray Bright Points of the Quiet Sun

Small-scale impulsive events, known as nanoflares, are thought to be one of the prime candidates that can keep the solar corona hot at its multimillion-Kelvin temperature. Individual nanoflares are difficult to detect with the current generation of instruments; however, their presence can be inferred through indirect techniques such as Differential Emission Measure (DEM) analysis. Here, we employ this technique to investigate the possibility of nanoflare heating of the quiet corona during the minimum of solar cycle 24. We estimate the DEM of disk-integrated quiet Sun and X-ray bright points (XBP) using the observations from XSM on board the Chandrayaan-2 orbiter and AIA on board the Solar Dynamic Observatory. XBPs are found to be the dominant contributor to disk-integrated X-rays, with a radiative flux of ~2 × 105 erg cm-2 s-1. XBPs consist of small-scale loops associated with bipolar magnetic fields. We simulate such XBP loops using the EBTEL hydrodynamic code. The lengths and magnetic field strengths of these loops are obtained through a potential field extrapolation of the photospheric magnetogram. Each loop is assumed to be heated by random nanoflares having an energy that depends on the loop properties. The composite nanoflare energy distribution for all the loops has a power-law slope close to -2.5. The simulation output is then used to obtain the integrated DEM. It agrees remarkably well with the observed DEM at temperatures above 1 MK, suggesting that the nanoflare distribution, as predicted by our model, can explain the XBP heating.

Keywords: solar coronal heating; x-ray bright point; solar flares; solar coronal loops; solar x-ray emission; quiet solar corona; quiet sun
Observations and Simulations of Radio Emission and Magnetic Fields in Minkowski's Object

We combine new data from the Karl G. Jansky Very Large Array with previous radio observations to create a more complete picture of the ongoing interactions between the radio jet from galaxy NGC 541 and the star-forming system known as Minkowski's Object (MO). We then compare those observations with synthetic radio data generated from a new set of magnetohydrodynamic simulations of jet-cloud interactions specifically tailored to the parameters of MO. The combination of radio intensity, polarization, and spectral index measurements all convincingly support the interaction scenario and provide additional constraints on the local dynamical state of the intracluster medium and the time since the jet-cloud interaction first began. In particular, we show that only a simulation with a bent radio jet can reproduce the observations.

Keywords: galaxy jets; magnetohydrodynamical simulations; radio galaxies; tailed radio galaxies; jets
Highly Resolved Topography and Illumination at Mercury's South Pole from MESSENGER MDIS NAC

Mercury's south polar region is of particular interest since Arecibo radar measurements show many high-reflectance regions consistent with ice deposits. However, current elevation information in Mercury's southern hemisphere is not sufficient to perform detailed modeling of the illumination and thermal conditions at these radar-bright locations and to constrain properties of the volatiles potentially residing there. In this work, we leverage previously existing elevation maps of Mercury's surface from stereo-photogrammetry at 665 m pix-1, Mercury Dual Imaging System Narrow Angle Camera images, and Shape-from-Shading tools from the Ames Stereo Pipeline, to provide the first high-resolution topographic maps of the south pole with a resolution of 250 m pix-1 poleward of 75°S. We show that the increased resolution and level of detail provided by our new elevation model allow for a more realistic recovery of illumination conditions in Mercury's south polar region, thus opening the way to future thermal analyses and for the characterization of potential ice and volatile deposits. We compare both the old and new topographic models to the Mercury Dual Imaging System Narrow Angle Camera images to show the higher level of fidelity with our products, and we assess the improved consistency of derived permanently shadowed regions with reflectance measurements by Arecibo's antennas.

Keywords: mercury (planet); remote sensing; planetary polar regions; planetary surfaces; surface ices
Identifying Changing-look AGNs Using Variability Characteristics

Changing-look (CL) active galactic nuclei (AGNs), characterized by the appearance/disappearance of broad emission lines in the span of a few years, present a challenge for the AGN unified model, whereby the Type 1 versus Type 2 dichotomy results from orientation effects alone. We present a systematic study of a large sample of spectroscopically classified AGNs, using optical variability data from the Zwicky Transient Facility (ZTF) as well as follow-up spectroscopy data. We demonstrate that Type 1 and Type 2 AGNs can be neatly separated on the basis of the variability metric σ QSO, which quantifies the resemblance of a light curve to a damped random walk model. For a small subsample, however, the ZTF light curves are inconsistent with their previous classification, suggesting the occurrence of a CL event. Specifically, we identify 35 (12) turn-on (turn-off) CL AGN candidates at z < 0.35. Based on follow-up spectroscopy, we confirm 17 (4) turn-on (turn-off) CL AGNs out of 21 (5) candidates, representing a high success rate for our method. Our results suggest that the occurrence rate of CL AGNs is ∼0.3% over timescales of 5–20 yr, and confirm that the CL transition typically occurs at an Eddington ratio of ≲0.01.

Keywords: quasars; active galactic nuclei