adsabs/SciX_UAT_keywords huggingface dataset:
FEASTS Combined with Interferometry. I. Overall Properties of Diffuse H I and Implications for Gas Accretion in Nearby Galaxies

We present a statistical study of the properties of diffuse H I in 10 nearby galaxies, comparing the H I detected by the single-dish telescope FAST (FEASTS program) and the interferometer Very Large Array (THINGS program), respectively. The THINGS observation missed H I with a median of 23% due to the short-spacing problem of interferometry and limited sensitivity. We extract the diffuse H I by subtracting the dense H I, which is obtained from the THINGS data with a uniform flux-density threshold, from the total H I detected by FAST. Among the sample, the median diffuse-H I fraction is 34%, and more diffuse H I is found in galaxies exhibiting more prominent tidal-interaction signatures. The diffuse H I we detected seems to be distributed in disk-like layers within a typical thickness of 1 kpc, different from the more halo-like diffuse H I detected around NGC 4631 in a previous study. Most of the diffuse H I is cospatial with the dense H I and has a typical column density of 1017.7–1020.1 cm‑2. The diffuse and dense H I exhibit a similar rotational motion, but the former lags by a median of 25% in at least the inner disks, and its velocity dispersions are typically twice as high. Based on a simplified estimation of circumgalactic medium properties and assuming pressure equilibrium, the volume density of diffuse H I appears to be constant within each individual galaxy, implying its role as a cooling interface. Comparing with existing models, these results are consistent with a possible link between tidal interactions, the formation of diffuse H I, and gas accretion.

Keywords: interstellar atomic gas; galaxy formation; circumgalactic medium; galaxy evolution
CSST Strong-lensing Preparation: A Framework for Detecting Strong Lenses in the Multicolor Imaging Survey by the China Survey Space Telescope (CSST)

Strong gravitational lensing is a powerful tool for investigating dark matter and dark energy properties. With the advent of large-scale sky surveys, we can discover strong-lensing systems on an unprecedented scale, which requires efficient tools to extract them from billions of astronomical objects. The existing mainstream lens-finding tools are based on machine-learning algorithms and applied to cutout-centered galaxies. However, according to the design and survey strategy of optical surveys by the China Space Station Telescope (CSST), preparing cutouts with multiple bands requires considerable efforts. To overcome these challenges, we have developed a framework based on a hierarchical visual transformer with a sliding window technique to search for strong-lensing systems within entire images. Moreover, given that multicolor images of strong-lensing systems can provide insights into their physical characteristics, our framework is specifically crafted to identify strong-lensing systems in images with any number of channels. As evaluated using CSST mock data based on a semianalytic model named CosmoDC2, our framework achieves precision and recall rates of 0.98 and 0.90, respectively. To evaluate the effectiveness of our method in real observations, we have applied it to a subset of images from the DESI Legacy Imaging Surveys and media images from Euclid Early Release Observations. A total of 61 new strong-lensing system candidates are discovered by our method. However, we also identified false positives arising primarily from the simplified galaxy morphology assumptions within the simulation. This underscores the practical limitations of our approach while simultaneously highlighting potential avenues for future improvements.

Keywords: strong gravitational lensing; astronomy image processing; neural networks; space telescopes
The Outer Edge of the Venus Zone around Main-sequence Stars

A key item of interest for planetary scientists and astronomers is the habitable zone: the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface. However, when observing a system's habitable zone, it is possible that one may instead observe a Venus-like planet. We define "Venus-like" as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includes both incipient and post-runaway greenhouse states. Both the possibility of observing a Venus-like world and the possibility that Venus could represent an end state of evolution for habitable worlds require an improved understanding of the Venus-like planet, specifically the distances where these planets can exist. Understanding this helps us define a "Venus zone"-the region in which Venus-like planets could exist-and assess the overlap with the aforementioned "habitable zone." In this study, we use a 1D radiative-convective climate model to determine the outer edge of the Venus zone for F0V, G2V, K5V, and M3V and M5V stellar spectral types. Our results show that the outer edge of the Venus zone resides at 3.01, 1.36, 0.68, 0.23, and 0.1 au, respectively. These correspond to incident stellar fluxes of 0.8, 0.55, 0.38, 0.32, and 0.3 S ⊙, respectively, where stellar flux is relative to Earth (1.0). These results indicate that there may be considerable overlap between the habitable zone and the Venus zone.

Keywords: venus; carbon dioxide; greenhouse gases; habitable zone
Reverberation Mapping Measurements of Black Hole Masses and Broad-line Region Kinematics in Mrk 817 and NGC 7469

We present the results from a spectroscopic monitoring campaign to obtain reverberation mapping measurements and investigate the broad-line region (BLR) kinematics for active galactic nuclei (AGNs) of Mrk 817 and NGC 7469. This campaign was undertaken with the Lijiang 2.4 m telescope. The median spectroscopic sampling is 2.0 days for Mrk 817 and 1.0 day for NGC 7469. We detect time lags of the broad emission lines, including Hβ, Hγ, He II, and He I for both AGNs, including Fe II for Mrk 817 with respect to the varying AGN continuum at 5100 Å. Investigating the relationship between line widths and time lags of the broad emission lines, we find that the BLR dynamics of Mrk 817 and NGC 7469 are consistent with the virial prediction. We estimate the masses of central supermassive black holes (SMBHs) and the accretion rates of both AGNs. Using the data of this campaign, we construct the velocity-resolved lag profiles of the broad Hγ, Hβ, and He I lines for Mrk 817, which show almost the same kinematic signatures in that the time lags in the red wing are slightly larger than the time lags in the blue wing. For NGC 7469, we only clearly construct the velocity-resolved lag profiles of the broad Hγ and Hβ, which show very similar kinematic signatures to the BLR of Mrk 817. These signatures indicate that the BLR of Keplerian motion in both AGNs seemingly has outflowing components during the monitoring period. We discuss the kinematics of the BLR and the measurements, including SMBH mass and accretion rates.

Keywords: seyfert galaxies; supermassive black holes; reverberation mapping; time domain astronomy
Parker Solar Probe Observations of Proton Beams Simultaneous with Ion-scale Waves

Parker Solar Probe (PSP), NASA's latest and closest mission to the Sun, is on a journey to investigate fundamental enigmas of the inner heliosphere. This paper reports initial observations made by the Solar Probe Analyzer for Ions (SPAN-I), one of the instruments in the Solar Wind Electrons Alphas and Protons instrument suite. We address the presence of secondary proton beams in concert with ion-scale waves observed by FIELDS, the electromagnetic fields instrument suite. We show two events from PSP's second orbit that demonstrate signatures consistent with wave-particle interactions. We showcase 3D velocity distribution functions (VDFs) measured by SPAN-I during times of strong wave power at ion scales. From an initial instability analysis, we infer that the VDFs departed far enough away from local thermodynamic equilibrium to provide sufficient free energy to locally generate waves. These events exemplify the types of instabilities that may be present and, as such, may guide future data analysis characterizing and distinguishing between different wave-particle interactions.

Keywords: solar wind; space plasmas; plasma physics; alfven waves
Comparative Study of Data-driven Solar Coronal Field Models Using a Flux Emergence Simulation as a Ground-truth Data Set

For a better understanding of the magnetic field in the solar corona and dynamic activities such as flares and coronal mass ejections, it is crucial to measure the time-evolving coronal field and accurately estimate the magnetic energy. Recently, a new modeling technique called the data-driven coronal field model, in which the time evolution of magnetic field is driven by a sequence of photospheric magnetic and velocity field maps, has been developed and revealed the dynamics of flare-productive active regions. Here we report on the first qualitative and quantitative assessment of different data-driven models using a magnetic flux emergence simulation as a ground-truth (GT) data set. We compare the GT field with those reconstructed from the GT photospheric field by four data-driven algorithms. It is found that, at minimum, the flux rope structure is reproduced in all coronal field models. Quantitatively, however, the results show a certain degree of model dependence. In most cases, the magnetic energies and relative magnetic helicity are comparable to or at most twice of the GT values. The reproduced flux ropes have a sigmoidal shape (consistent with GT) of various sizes, a vertically standing magnetic torus, or a packed structure. The observed discrepancies can be attributed to the highly non-force-free input photospheric field, from which the coronal field is reconstructed, and to the modeling constraints such as the treatment of background atmosphere, the bottom boundary setting, and the spatial resolution.

Keywords: magnetohydrodynamics; solar active regions; solar corona; solar photosphere; solar magnetic fields; solar magnetic flux emergence; solar flares; solar coronal mass ejections
Wind Roche-lobe Overflow in Low-mass Binaries: Exploring the Origin of Rapidly Rotating Blue Lurkers

Wind Roche-lobe overflow (WRLOF) is a mass-transfer mechanism proposed by Mohamed and Podsiadlowski for stellar binaries wherein the wind acceleration zone of the donor star exceeds its Roche-lobe radius, allowing stellar wind material to be transferred to the accretor at enhanced rates. WRLOF may explain characteristics observed in blue lurkers and blue stragglers. While WRLOF has been implemented in rapid population synthesis codes, it has yet to be explored thoroughly in detailed binary models such as MESA (a 1D stellar evolution code), and over a wide range of initial binary configurations. We incorporate WRLOF accretion in MESA to investigate wide low-mass binaries at solar metallicity. We perform a parameter study over the initial orbital periods and stellar masses. In most of the models where we consider angular momentum transfer during accretion, the accretor is spun up to the critical (or breakup) rotation rate. Then we assume the star develops a boosted wind to efficiently reduce the angular momentum so that it could maintain subcritical rotation. Balanced by boosted wind loss, the accretor only gains ∼2% of its total mass, but can maintain a near-critical rotation rate during WRLOF. Notably, the mass-transfer efficiency is significantly smaller than in previous studies in which the rotation of the accretor is ignored. We compare our results to observational data of blue lurkers in M67 and find that the WRLOF mechanism can qualitatively explain the origin of their rapid rotation, their location on the H-R diagram, and their orbital periods.

Keywords: binary stars; close binary stars; blue straggler stars; stellar evolution; low mass stars; stellar mass loss; stellar winds; wide binary stars
Voyager Observations of Electron Densities in the Very Local Interstellar Medium

The two Voyager spacecraft have now been immersed in the very local interstellar medium for several years. Both spacecraft carry a plasma wave instrument capable of detecting plasma waves that yield electron density through the determination of the electron plasma frequency. Recent observations by Voyager 1 show increases in density at shocks and pressure fronts that are commensurate with increases in the magnetic field at these structures. Voyager 1 has not observed electron plasma oscillations, thought to be a signature of a nearby shock, since 2019, although Voyager 2 continues to observe these as recently as 2022 November. Voyager 1 also detects a faint thermal emission at the electron plasma frequency that shows the evolution of the plasma density as Voyager moves deeper into the medium. Here, we show the most recent observations from both Voyagers showing the increasing densities in the region upstream of the heliopause. We also investigate the fate of solar transients as they move ever deeper into the interstellar medium.

Keywords: interstellar medium; interstellar plasma; interstellar medium wind; space plasmas; astrosphere interstellar medium interactions
The Host Galaxy of the Recoiling Black Hole Candidate in 3C 186: An Old Major Merger Remnant at the Center of a z = 1 Cluster

3C 186, a radio-loud quasar at z = 1.0685, was previously reported to have both velocity and spatial offsets from its host galaxy, and has been considered as a promising candidate for a gravitational wave recoiling black hole triggered by a black hole merger. Another possible scenario is that 3C 186 is in an ongoing galaxy merger, exhibiting a temporary displacement. In this study, we present analyses of new deep images from the Hubble Space Telescope WFC3-IR and Advanced Camera for Surveys, aiming to characterize the host galaxy and test this alternative scenario. We carefully measure the light-weighted center of the host and reveal a significant spatial offset from the quasar core (11.1 ± 0.1 kpc). The direction of the confirmed offset aligns almost perpendicularly to the radio jet. We do not find evidence of a recent merger, such as a young starburst in disturbed outskirts, but only marginal light concentration in F160W at ~30 kpc. The host consists of mature (≳200 Myr) stellar populations and one compact star-forming region. We compare with hydrodynamical simulations and find that those observed features are consistently seen in late-stage merger remnants. Taken together, those pieces of evidence indicate that the system is not an ongoing/young merger remnant, suggesting that the recoiling black hole scenario is still a plausible explanation for the puzzling nature of 3C 186.

Keywords: active galaxies; gravitational waves
No Longer Ballistic, Not Yet Diffusive-the Formation of Cosmic-Ray Small-scale Anisotropies

The arrival directions of TeV-PeV cosmic rays are remarkably uniform due to the isotropization of their directions by scattering on turbulent magnetic fields. Small anisotropies can exist in standard diffusion models, however, only on the largest angular scales. Yet, high-statistics observatories like IceCube and High-Altitude Water Cherenkov Observatory have found significant deviations from isotropy down to small angular scales. Here, we explain the formation of small-scale anisotropies by considering pairs of cosmic rays that get correlated by their transport through the same realization of the turbulent magnetic field. We argue that the formation of small-scale anisotropies is the reflection of the particular realization of the turbulent magnetic field experienced by cosmic rays on timescales intermediate between the early, ballistic regime and the late, diffusive regime. We approach this problem in two different ways: First, we run test particle simulations in synthetic turbulence, covering for the first time the TV rigidities of observations with realistic turbulence parameters. Second, we extend the recently introduced mixing matrix approach and determine the steady-state angular power spectrum. Throughout, we adopt magneto-static, slab-like turbulence. We find excellent agreement between the predicted angular power spectra in both approaches over a large range of rigidities. In the future, measurements of small-scale anisotropies will be valuable in constraining the nature of the turbulent magnetic field in our Galactic neighborhood.

Keywords: galactic cosmic rays; perturbation methods; interstellar magnetic fields; milky way magnetic fields
FAST-ASKAP Synergy: Quantifying Coexistent Tidal and Ram Pressure Strippings in the NGC 4636 Group

Combining new H I data from a synergetic survey of Australian Square Kilometre Array Pathfinder (ASKAP) Widefield ASKAP L-band Legacy All-sky Blind surveY and Five-hundred-meter Aperture Spherical radio Telescope with the Arecibo Legacy Fast ALFA data, we study the effect of ram pressure and tidal interactions in the NGC 4636 group. We develop two parameters to quantify and disentangle these two effects on gas stripping in H I-bearing galaxies: the strength of external forces at the optical-disk edge, and the outside-in extents of H I-disk stripping. We find that gas stripping is widespread in this group, affecting 80% of H I-detected nonmerging galaxies, and that 41% are experiencing both types of stripping. Among the galaxies experiencing both effects, the two types of strengths are independent, while two H I-stripping extents moderately anticorrelate with each other. Both strengths are correlated with H I-disk shrinkage. The tidal strength is related to a rather uniform reddening of low-mass galaxies (M * < 109 M ☉) when tidal stripping is the dominating effect. In contrast, ram pressure is not clearly linked to the color-changing patterns of galaxies in the group. Combining these two stripping extents, we estimate the total stripping extent, and put forward an empirical model that can describe the decrease of H I richness as galaxies fall toward the group center. The stripping timescale we derived decreases with distance to the center, from ~1 Gyr beyond R 200 to ≲10 Myr near the center. Gas depletion happens ~3 Gyr since crossing 2R 200 for H I-rich galaxies, but much quicker for H I-poor ones. Our results quantify in a physically motivated way the details and processes of environmental-effects-driven galaxy evolution, and might assist in analyzing hydrodynamic simulations in an observational way.

Keywords: galaxies; interstellar atomic gas; galaxy evolution; galaxy environments
Filament Eruption from Active Region 13283 Leading to a Fast Halo-CME and an Intense Geomagnetic Storm on 2023 April 23

Using multi-instrument and multiwavelength observations, we studied a coronal mass ejection (CME) that led to an intense geomagnetic storm on 2023 April 23. The eruption occurred on April 21 in solar active region (AR) 13283 near the disk center. The AR was in its decay stage, with fragmented polarities and a preexisting long filament channel a few days before the eruption. The study of the magnetic field evolution suggests that the flux rope (filament) was built up by monotonous helicity accumulation over several days, and furthermore, converging and canceling fluxes led to a change in helicity injection, resulting in an unstable nature of the magnetic flux rope (MFR) and its further eruption. Importantly, the CME morphology revealed that the MFR apex underwent a rotation of up to 56° in clockwise direction owing to its positive helicity. The CME decelerates in the field of view (FOV) of the Large Angle Spectrometric Coronagraph and has a plane-of-sky velocity of 1226 km s‑1 at 20 R ⊙. In the FOV of the Heliospheric Imager, the lateral expansion of the CME is tracked better than the earthward motion. This implies that the arrival time is difficult to assess. The in situ arrival of the interplanetary CME shock was at 07:30 UT on April 23, and a geomagnetic storm commenced at 08:30 UT. The flux rope fitting to the in situ magnetic field observations reveals that the magnetic cloud flux rope orientation is consistent with its near-Sun orientation, which has a strong negative Bz-component. The analysis of this study indicates that the near-Sun rotation of the filament during its eruption to the CME is the key to the negative Bz-component and consequently the intense geomagnetic storm.

Keywords: the sun
The 60 pc Environment of FRB 20180916B

Fast radio burst FRB 20180916B in its host galaxy SDSS J015800.28+654253.0 at 149 Mpc is by far the closest-known FRB with a robust host galaxy association. The source also exhibits a 16.35 day period in its bursting. Here we present optical and infrared imaging as well as integral field spectroscopy observations of FRB 20180916B with the WFC3 camera on the Hubble Space Telescope and the MEGARA spectrograph on the 10.4 m Gran Telescopio Canarias. The 60-90 milliarcsecond (mas) resolution of the Hubble imaging, along with the previous 2.3 mas localization of FRB 20180916B, allows us to probe its environment with a 30-60 pc resolution. We constrain any point-like star formation or H II region at the location of FRB 20180916B to have an Hα luminosity LHα ≲ 1037 erg s-1, and we correspondingly constrain the local star formation rate to be ≲10-4 M⊙ yr-1. The constraint on Hα suggests that possible stellar companions to FRB 20180916B should be of a cooler, less massive spectral type than O6V. FRB 20180916B is 250 pc away (in projected distance) from the brightest pixel of the nearest young stellar clump, which is ∼380 pc in size (FWHM). With the typical projected velocities of pulsars, magnetars, or neutron stars in binaries (60-750 km s-1), FRB 20180916B would need 800 kyr to 7 Myr to traverse the observed distance from its presumed birth site. This timescale is inconsistent with the active ages of magnetars (≲10 kyr). Rather, the inferred age and observed separation are compatible with the ages of high-mass X-ray binaries and gamma-ray binaries, and their separations from the nearest OB associations.

Keywords: magnetars; high mass x-ray binary stars; radio transient sources; hubble space telescope
Extremely Low Mass Ratio Contact Binaries. I. The First Photometric and Spectroscopic Investigations of Ten Systems

The photometric and spectroscopic investigations of ten contact binaries were presented for the first time. It is discovered that the mass ratios of all the ten targets are smaller than 0.15, they are extremely low mass ratio contact binaries. Seven of them are deep contact binaries, two are medium contact binaries, while only one is a shallow contact system. Five of them show the O'Connell effect, and a dark spot on one of the two components can lead to a good fit of the asymmetric light curves. The orbital period studies of the ten binaries reveal that they all exhibit long-term period changes, six of them are increasing, while the others are shrinking. The LAMOST spectra were analyzed by the spectral subtraction method, and all the ten targets exhibit excess emissions in the H α line, indicating chromospheric activity. The evolutionary states of the two components of the ten binaries were studied, and it is found that their evolutionary states are identical to those of the other contact binaries. Based on the study of the relation between orbital angular momentum and total mass, we discovered the ten systems may be at the late evolutionary stage of a contact binary. The initial masses of the two components and the ages of them were obtained. By calculating the instability parameters, we found that the ten contact binaries are relatively stable at present.

Keywords: close binary stars; eclipsing binary stars; contact binary stars; mass ratio; stellar activity; stellar evolution