adsabs/SciX_UAT_keywords huggingface dataset:
The Black Hole Mass of NGC 4151 from Stellar Dynamical Modeling

The mass of a supermassive black hole (MBH) is a fundamental property that can be obtained through observational methods. Constraining MBH through multiple methods for an individual galaxy is important for verifying the accuracy of different techniques and for investigating the assumptions inherent in each method. However, there exist only a few galaxies where multiple MBH measurement techniques can be applied. NGC 4151 is one of these rare galaxies for which multiple methods can be used: stellar and gas dynamical modeling because of its proximity (D = 15.8 ± 0.4 Mpc from Cepheids), and reverberation mapping because of its active accretion. In this work, we reanalyzed H-band integral field spectroscopy of the nucleus of NGC 4151 from Gemini NIFS, improving the analysis at several key steps. We then constructed a wide range of axisymmetric dynamical models with the new orbit-superposition code FORSTAND. One of our primary goals is to quantify the systematic uncertainties in MBH arising from different combinations of the deprojected density profile, inclination, intrinsic flattening, and mass-to-light ratio. As a consequence of uncertainties on the stellar luminosity profile arising from the presence of the active galactic nucleus, our constraints on MBH are rather weak. Models with a steep central cusp are consistent with no black hole; however, in models with more moderate cusps, the black hole mass lies within the range of 0.25 × 107 M⊙ ≲ MBH ≲ 3 × 107 M⊙. This measurement is somewhat smaller than the earlier analysis presented by Onken et al. but agrees with previous MBH values from gas dynamical modeling and reverberation mapping. Future dynamical modeling of reverberation data, as well as IFU observations with JWST, will aid in further constraining the mass of the central supermassive black hole in NGC 4151.

Keywords: active galaxies; seyfert galaxies; supermassive black holes
Synchronizing the EMRIs and IMRIs in AGN Accretion Disks

Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals (IMRIs) are important gravitational-wave (GW) sources for the Laser Interferometer Space Antenna (LISA). So far, their formation and evolution have been considered to be independent. However, recent theories suggest that stellar-mass black holes (sBHs) and intermediate-mass black hole (IMBHs) can coexist in the accretion disk of an active galactic nucleus (AGN), which indicates that EMRIs and IMRIs may form in the same place. Motivated by the fact that a gas giant migrating in a protoplanetary disk could trap planetesimals close to its orbit, in this paper we study a similar interaction between a gap-opening IMBH in an AGN disk and the sBHs surrounding it. We analyze the torques imposed on the sBHs by the disk and also by the IMBH, and show that the sBHs can be trapped by the IMBH if they are inside the orbit of the IMBH. We then implement the torques in our numerical simulations to study the migration of an outer IMBH and an inner sBH, which are both embedded in an AGN disk. We find that their migration is synchronized until they reach a distance of about 10 Schwarzschild radii from the central supermassive black hole, where the pair break up due to strong GW radiation. This result indicates that LISA may detect an EMRI and an IMRI within several years from the same AGN. This GW source will bring rich information about the formation and evolution of sBHs and IMBHs in AGNs.

Keywords: active galactic nuclei; intermediate-mass black holes; stellar mass black holes; gravitational waves
The Tail of Late-forming Dwarf Galaxies in ΛCDM

We use a robust analytical model together with a high-resolution hydrodynamical cosmological simulation to demonstrate that in a Lambda cold dark matter (ΛCDM) universe, a small fraction of dwarf galaxies inhabiting dark matter (DM) halos in the mass range 3 × 109 ≲ M200/M⊙ ≲ 1010 form unusually late (z < 3) compared to the bulk population of galaxies. These galaxies originate from the interplay between the stochastic growth of DM halos and the existence of a time-dependent DM halo mass below which galaxies do not form. The formation epoch of the simulated late-forming galaxies traces remarkably well the time when their host DM halos first exceeded a nontrivial (but well-understood) time-dependent critical mass, thus making late-forming dwarfs attractive cosmological probes with constraining power over the past growth history of their host halos. The agreement between our model and the simulation results demonstrates that the population of simulated late-forming dwarfs is a robust cosmological outcome and largely independent of the specific galaxy formation model included in the simulations provided: (1) the universe underwent cosmic reionization before ${z}_{\mathrm{re}}\sim 8;$ (2) star formation proceeds in gas that self-gravitates; and (3) galaxy formation is largely restricted to atomic-cooling halos before zre. The scarcity of massive late-forming dwarfs expected in ΛCDM implies that the great majority of bright, metal-poor, and actively star-forming dwarfs observed in our local universe-the most obvious candidates for these late-forming galaxies-cannot be undergoing their formation for the first time at the present day in a ΛCDM universe.

Keywords: dwarf galaxies; compact dwarf galaxies; galaxy formation; reionization
Multiwavelength View of the Close-by GRB 190829A Sheds Light on Gamma-Ray Burst Physics

We monitored the position of the close-by (about 370 Mpc) gamma-ray burst GRB 190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) observations with the European VLBI Network and the Very Long Baseline Array, carrying out a total of nine observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of a few milliarcseconds. From a state-of-the art analysis of these data, we obtained valuable limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modeling of the multiwavelength light curves with a forward-plus-reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the HESS data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the multiwavelength, high-cadence coverage of the afterglow, inherent degeneracies in the afterglow model are broken to a large extent, allowing us to capture some unique physical insights; we find a low prompt emission efficiency of ≲10-3, a low fraction of relativistic electrons in the forward shock downstream χ e < 13% (90% credible level), and a rapid decay of the magnetic field in the reverse shock downstream after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometry is not sufficiently tight as to exclude any off-axis viewing angle, but we can exclude the line of sight to have been more than ~2° away from the border of the gamma-ray-producing region based on compactness arguments.

Keywords: gamma-ray bursts; very long baseline interferometry; shocks; relativistic jets; relativistic aberration
The Challenge to MOND from Ultra-faint Dwarf Galaxies

Modified Newtonian dynamics (MOND) at low acceleration has been astonishingly powerful at explaining the rotation curve of galaxies and the relation between the baryonic content of the galaxies and their observed circular velocity, known as the baryonic TullyFisher relationship. It is known that MOND fails at explaining the observed velocity dispersion of the ultra-faint dwarf galaxies (UFDs) with the justification that UFDs are more prone to tidal disruption in MOND compared to cold dark matter model. We show that (i) the ratio of tidal to internal acceleration in UFDs is extremely low, (ii) there is no correlation between the deviation of UFDs from MONDs prediction as a function of tidal susceptibility, and (iii) recent constraints from Gaia proper motion analysis on the orbital parameters of the UFDs exacerbate the challenge to MOND. In particular, Gaia data indicate that Ursa Major I is experiencing a recent infall into the Milky Ways halo, and its inconsistency with MOND at the 7 level cannot be attributed to being an early infall satellite. Moreover, the new data from Gaia DR2 show Willman I to have the least eccentric orbit of all UFDs, and its deviation from MOND at the 4 level cannot be attributed to a highly eccentric orbit as previously suggested. Finally, given that Tuc III is the only UFD observed to show tidal features, Reticulum II and Segue I are two other UFDs that potentially challenge MOND as they have comparable Galactocentric distances to Tuc III while showing no tidal features.

Keywords: cold dark matter; modified newtonian dynamics; dwarf galaxies
Polar Dust Emission in Quasar IR SEDs and Its Correlation with Narrow-line Regions

Polar dust has been found to play an important role in the mid-infrared emission of nearby Seyfert nuclei. If and how often polar dust exists among the quasar population is unknown due to the lack of spatially resolved observations. In this Letter, we report correlations between the prominence of active galactic nucleus (AGN) forbidden line emission (commonly associated with the narrow-line region) and the dust mid-IR energy output among the archetypal Palomar-Green quasar sample and other bright type-1 AGNs drawn from the Sloan Digital Sky Survey, Spitzer, and Wide-field Infrared Survey Explorer (WISE) archives. The AGN mid-IR color differences traced by WISE W2 (~4.6 μm)-W3 (~12 μm) and W2 (~4.6 μm)-W4 (~22 μm), and near-IR to mid-IR spectral energy distributions (SEDs) constrained with the Two Micron All Sky Survey, WISE, and Spitzer data have clear trends with the relative strength of the forbidden line regions traced by the optical [O III] and mid-IR [O IV] emission lines. These observations indicate that, where the lines are strong, a large fraction of the AGN emission at λ ≳ 5 μm comes from dust in the forbidden line regions. We find that the widely quoted universal AGN template is a result of averaging quasar SEDs with different levels of polar dust emission above the torus output and that the typical intrinsic IR SED of compact torus dust emission alone falls with increasing wavelength past 5 μm (in νF ν ). In addition, the association of polar dust with the forbidden lines suggests an alternative to the receding torus hypothesis for the decrease in infrared output with increasing AGN luminosity.

Keywords: active galactic nuclei; dust continuum emission; quasars; spectral energy distribution
Bi-lognormal Distribution of Sunspot Group Areas

We use daily observations from the Royal Greenwich Observatory and Kislovodsk Mountain Astronomical Station of Pulkovo Observatory to study the distribution properties of sunspot areas. To mitigate the poor statistics in the distribution of small areas, we introduce a "precision randomization" approach based on the assumption that all measured areas have a random component within the measurement uncertainty of 1 millionth of the solar hemisphere (M.S.H.). We confirm the presence of two distinct components in the distribution of sunspots previously reported by several authors, and show that the area distribution is described by the sum of two lognormal distributions responsible for small and large groups (sunspots), respectively. We also demonstrate that the area of the main spots in the groups correlates well with the total area of the group, and, thus, the findings derived for the total group areas are equally applicable to the main spots of groups.

Keywords: sunspots
A High-Eccentricity Warm Jupiter Orbiting TOI-4127

We report the discovery of TOI-4127 b, which is a transiting, Jupiter-sized exoplanet on a long-period ( $P={56.39879}_{-0.00010}^{+0.00010}$ days) and a high-eccentricity orbit around a late F-type dwarf star. This warm Jupiter was first detected and identified as a promising candidate from a search for single-transit signals in TESS Sector 20 data, and was later characterized as a planet following two subsequent transits (TESS Sectors 26 and 53) and follow-up ground-based RV observations with the NEID and SOPHIE spectrographs. We jointly fit the transit and RV data to constrain the physical ( ${R}_{p}={1.096}_{-0.032}^{+0.039}{R}_{{\rm{J}}}$ , ${M}_{p}={2.30}_{-0.11}^{+0.11}{M}_{{\rm{J}}}$ ) and orbital parameters of the exoplanet. Given its high orbital eccentricity ( $e={0.7471}_{-0.0086}^{+0.0078}$ ), TOI-4127 b is a compelling candidate for studies of warm Jupiter populations and of hot Jupiter formation pathways. We show that the present periastron separation of TOI-4127 b is too large for high-eccentricity tidal migration to circularize its orbit, and that TOI-4127 b is unlikely to be a hot Jupiter progenitor unless it is undergoing angular momentum exchange with an undetected outer companion. Although we find no evidence for an external companion, the available observational data are insufficient to rule out the presence of a perturber that can excite eccentricity oscillations and facilitate tidal migration.

Keywords: exoplanet astronomy; exoplanet dynamics; transit photometry; radial velocity; elliptical orbits
Detailed Model of the Growth of Fluffy Dust Aggregates in a Protoplanetary Disk: Effects of Nebular Conditions

The coagulation of dust aggregates plays an important role in the formation of planets and is of key importance to the evolution of protoplanetary disks (PPDs). The characteristics of dust, such as the diversity of particle size, porosity, charge, and the manner in which dust couples to turbulent gas, affect the collision outcome and the rate of dust growth. Here we present a numerical model of the evolution of the dust population within a PPD which incorporates all of these effects. The probability that any two particles collide depends on the particle charge, cross-sectional area, and their relative velocity. The actual collision outcome is determined by a detailed collision model that takes into account the aggregate morphology, trajectory, orientation, and electrostatic forces acting between charged grains. Our model is applicable to the epoch of time during which hit-and-stick is the primary collision outcome, the duration of which varies greatly depending on the environment. The data obtained in this research reveal the characteristics of dust populations in different environments at the end of the hit-and-stick growth, which establishes the foundation for the onset of the next growth stage where bouncing, mass transfer, and fragmentation become important. For a given level of turbulence, neutral and weakly charged particles collide more frequently and grow faster than highly charged particles. In general, the epoch of hit-and-stick growth is much shorter in high turbulence than it is in regions with low turbulence or highly charged grains. In addition, highly charged particles grow to a larger size before reaching the bouncing barrier, especially in environments with low turbulence, and exhibit "runaway" growth, in which a few large particles grow quickly by accreting smaller particles while the rest of the population grows very slowly. In general, highly charged aggregates have a more compact structure and are comprised of larger monomers than neutral/weakly charged aggregates. The differences in the particle structure/composition not only affect the threshold velocities for bouncing and fragmentation, but also change the scattering and absorption opacity of dust, influencing the appearance of PPDs.

Keywords: protoplanetary disks; space plasmas; circumstellar dust
Predicting the Redshift of γ-Ray-loud AGNs Using Supervised Machine Learning

Active galactic nuclei (AGNs) are very powerful galaxies characterized by extremely bright emissions coming from their central massive black holes. Knowing the redshifts of AGNs provides us with an opportunity to determine their distance to investigate important astrophysical problems, such as the evolution of the early stars and their formation, along with the structure of early galaxies. The redshift determination is challenging because it requires detailed follow-up of multiwavelength observations, often involving various astronomical facilities. Here we employ machine-learning algorithms to estimate redshifts from the observed γ-ray properties and photometric data of γ-ray-loud AGNs from the Fourth Fermi-LAT Catalog. The prediction is obtained with the Superlearner algorithm using a LASSO-selected set of predictors. We obtain a tight correlation, with a Pearson correlation coefficient of 71.3% between the inferred and observed redshifts and an average Δznorm = 11.6 × 10-4. We stress that, notwithstanding the small sample of γ-ray-loud AGNs, we obtain a reliable predictive model using Superlearner, which is an ensemble of several machine-learning models.

Keywords: active galactic nuclei
Identification of an [α/Fe]—Enhanced Thick Disk Component in an Edge-on Milky Way Analog

The Milky Way disk consists of two prominent components—a thick, alpha-rich, low-metallicity component and a thin, metal-rich, low-alpha component. External galaxies have been shown to contain thin- and thick-disk components, but whether distinct components in the [α/Fe]-[Z/H] plane exist in other Milky Way-like galaxies is not yet known. We present Very Large Telescope (VLT)—Multi Unit Spectroscopic Explorer (MUSE) observations of UGC 10738, a nearby, edge-on Milky Way-like galaxy. We demonstrate through stellar population synthesis model fitting that UGC 10738 contains alpha-rich and alpha-poor stellar populations with similar spatial distributions to the same components in the Milky Way. We discuss how the finding that external galaxies also contain chemically distinct disk components may act as a significant constraint on the formation of the Milky Way's own thin and thick disk.

Keywords: galaxy evolution; milky way evolution; disk galaxies; galaxy stellar content
Application of The Wind-driven Model to a Sample of Tidal Disruption Events

An origin of the optical/ultraviolet (UV) radiation from tidal disruption events (TDEs) has recently been discussed for different scenarios, but observational support is generally lacking. In this Letter, we test the applicability of the "wind-driven model" for a sample of UV/optical TDEs. With the model, we aim to derive the physical properties of the optical/UV TDEs, such as mass-loss rates and characteristic radii. The model assumes optically thick continuous outflows like stellar winds, and one key question arises: how is the wind-launched radius connected to physical processes in TDEs? Here we propose one possibility: through a comparison between the escape velocities estimated from their black hole masses and the wind velocities estimated from observed line widths, the outflow is launched from the self-interaction radius (RSI) where the stellar debris stretched by the tidal force intersects. We show that the escape velocities at RSI are roughly consistent with the wind velocities. By applying the model to a sample of optical/UV TDE candidates, we find that explosive mass ejections (≳10 M⊙ yr-1) from RSI (∼1014 cm) can explain the observed properties of TDEs around peak luminosity. We also apply the same framework to a peculiar transient, AT2018cow. This model suggests that AT2018cow is likely a TDE induced by an intermediate-mass black hole (MBH ∼ 104 M⊙).

Keywords: transient sources; tidal disruption; stellar winds
The First Light Curve Modeling and Orbital Period Change Investigation of Nine Contact Binaries around the Short-period Cutoff

In this paper, we present the first light curve synthesis and orbital period change analysis of nine contact binaries around the short-period limit. It is found that all these systems are W-subtype contact binaries. One of them is a medium contact system while the others are shallow contact ones. Four of them manifest obvious O'Connell effect explained by a dark spot or hot spot on one of the component stars. Third light was detected in three systems. By investigating orbital period variations, we found that four of the targets display a secular period decrease while the others exhibit a long-term period increase. The secular period decrease is more likely caused by angular-momentum loss while the long-term period increase is due to mass transfer from the less massive component to the more massive one. Based on the statistic of 19 ultrashort-period contact binaries with known orbital period changes, we found that seven of them display long-term decrease (three of them also exhibit cyclic variations), ten of them manifest long-term increase while two of them only show cyclic variation, and that most of them are shallow contact binaries supporting the long timescale angular-momentum loss theory suggested by Stepien. For the three deep contact systems, we found that they are probably triple systems. The tertiary companion plays an essential role during their formation and evolution.

Keywords: close binary stars; eclipsing binary stars; stellar evolution
Hot Plasma Flows and Oscillations in the Loop-top Region During the 2017 September 10 X8.2 Solar Flare

In this study, we investigate motions in the hot plasma above the flare loops during the 2017 September 10 X8.2 flare event. We examine the region to the south of the main flare arcade, where there is data from the Interface Region Imaging Spectrograph (IRIS) and the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. We find that there are initial blueshifts of 20-60 km s-1 observed in this region in the Fe XXI line in IRIS and the Fe XXIV line in EIS, and that the locations of these blueshifts move southward along the arcade over the course of about 10 minutes. The cadence of IRIS allows us to follow the evolution of these flows, and we find that at each location where there is an initial blueshift in the Fe XXI line, there are damped oscillations in the Doppler velocity with periods of ∼400 s. We conclude that these periods are independent of loop length, ruling out magnetoacoustic standing modes as a possible mechanism. Microwave observations from the Expanded Owens Valley Solar Array (EOVSA) indicate that there are nonthermal emissions in the region where the Doppler shifts are observed, indicating that accelerated particles are present. We suggest that the flows and oscillations are due to motions of the magnetic field that are caused by reconnection outflows disturbing the loop-top region.

Keywords: active solar corona; solar flares; solar magnetic reconnection
Reverse Shock Revisited in Cassiopeia A with Chandra

Using data from the Chandra X-ray Observatory, we revisit the reverse shock in the supernova remnant (SNR) Cassiopeia A. Based on spectroscopy of a series of annuli in the northwest (NW) and southeast (SE), we get the radial profiles of the S/Si Kα line flux ratio and Fe Kα line centroid energy. They both show monotonic increase, confirming that the Si- and Fe-rich ejecta are heated by the reverse shock. The abrupt change of the S and Si line flux ratio is clearly observed in Cassiopeia A, leading to the determination of the reverse-shock location (∼1.'71 0.'16 and ∼1.'35 0.'18 in the NW and SE, with respect to the central source). By comparing the radial profiles of the S and Si line flux, we find that the reverse shock is moving outward in the frame of the observer, and the velocities are ∼3950 ± 210 km s‑1 and ∼2900 ± 260 km s‑1 in the NW and SE, respectively. In contrast, the velocities become ∼1150 km s‑1 (NW) and ∼1300 km s‑1 (SE) in the ejecta frame. Our measured reverse-shock velocities are quite consistent with those obtained from the X-ray and/or optical images. They therefore supply a cross-check of the accuracy for the two available methods for measuring the reverse-shock velocity in SNRs. Both the location and the velocity of the reverse shock show apparent asymmetry, suggesting that the asymmetric explosion of the progenitor plays a key role in the interaction between the reverse shock and the ejecta, ultimately shaping the complex features observed in SNRs.

Keywords: supernova remnants; interstellar medium; x-ray astronomy; shocks