adsabs/SciX_UAT_keywords huggingface dataset:
Remarkable Correspondence of the Sagittarius A* Submillimeter Variability with a Stellar-wind-fed Accretion Flow Model

We compare the 230 GHz near-horizon emission from Sagittarius A* to simulations representing three classes of accretion flows. Using the structure function to capture the variability statistics of the light curve, we find a noticeable discrepancy between the observations and models based on torus-fed accretion disks, whether those disks bring in a small or large amount of net magnetic flux. On the other hand, the simulations that are fed more realistically by stellar winds match the observed structure function very well. We describe the differences between models, arguing that feeding by stellar winds may be a critical component in constructing theoretical models for accretion in the Galactic Center.

Keywords: supermassive black holes; low-luminosity active galactic nuclei; galactic center; magnetohydrodynamics; astrophysical fluid dynamics; astrophysical black holes; accretion; general relativity; stellar winds; magnetohydrodynamical simulations
Decomposing the Origin of TeV-PeV Emission from the Galactic Plane: Implications of Multimessenger Observations

High-energy neutrino and γ-ray emission has been observed from the Galactic plane, which may come from individual sources and/or diffuse cosmic rays. We evaluate the contribution of these two components through the multimessenger connection between neutrinos and γ-rays in hadronic interactions. We derive maximum fluxes of neutrino emission from the Galactic plane using γ-ray catalogs, including 4FGL, HGPS, 3HWC, and 1LHAASO, and measurements of the Galactic diffuse emission by Tibet ASγ and LHAASO. We find that the IceCube Galactic neutrino flux is larger than the contribution from all resolved sources when excluding promising leptonic sources such as pulsars, pulsar wind nebulae, and TeV halos. Our result indicates that the Galactic neutrino emission is likely dominated by the diffuse emission by the cosmic-ray sea and unresolved hadronic γ-ray sources. In addition, the IceCube flux is comparable to the sum of the flux of nonpulsar sources and the LHAASO diffuse emission especially above ~30 TeV. This implies that the LHAASO diffuse emission may dominantly originate from hadronic interactions, either as the truly diffuse emission or unresolved hadronic emitters. Future observations of neutrino telescopes and air-shower γ-ray experiments in the Southern hemisphere are needed to accurately disentangle the source and diffuse emission of the Milky Way.

Keywords: neutrino astronomy; high-energy cosmic radiation
A Catalog of Holes and Shells in the Interstellar Medium of the LITTLE THINGS Dwarf Galaxies

We present a catalog of holes and shells in the neutral atomic hydrogen (H I) of 41 gas-rich dwarf galaxies in LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey). We analyzed their properties as part of an investigation into the relation between star formation and structures and kinematics in the H I of small galaxies. We confirmed 306 holes between 38 pc (our resolution limit) and 2.3 kpc, with expansion velocities up to 30 km s-1. The global star formation rates (SFRs) measured by Hα and far-UV (FUV) emission are consistent with those estimated from the energy required to create the cataloged holes in our sample. Although we found no obvious correlation between global SFRs and the H I surface and volume porosities of our sample, two of the four galaxies with the lowest porosity and the two galaxies with the highest porosity have no recent star formation as measured by Hα and FUV emission.

Keywords: dwarf irregular galaxies; hi shells; interstellar medium; star formation
Observations of Whistler-mode Waves and Large-amplitude Electrostatic Waves Associated with a Dipolarization Front in the Bursty Bulk Flow

Plasma jets and jet fronts are common phenomena in planetary magnetospheres. They are usually associated with many plasma waves and can play a key role in the energy conversion, the excitation of wave emissions, particle acceleration, and the evolution of many astrophysical phenomena, which are major issues in the study of helio-terrestrial space physics. In this paper, we carefully investigated the properties of the whistler-mode wave and large-amplitude electrostatic wave in a plasma jet (bursty bulk flow (BBF)) using the Magnetospheric Multiscale mission data on the Earth's magnetosphere. At the leading part of the BBF, intense whistler-mode waves were observed inside the ion mirror-mode structures, which should be excited by the perpendicular temperature anisotropy of trapping electrons. A small-scale dipolarization front (DF) was then observed at the center of this BBF as a boundary between the leading and trailing parts of the BBF. Behind the DF, both an ion mirror-mode structure and whistler-mode waves disappear, while a large-amplitude electrostatic wave was detected and was associated with the cold ions at the trailing part of the BBF. The electrostatic wave is supposed to be generated by ion beam instability. These results will significantly improve the understanding of the kinetic process associated with the important boundary layer DF within plasma jets. The corresponding wave-particle interaction in space and the plasma environment can be further understood.

Keywords: space plasmas; plasma jets
First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPR

We present a comprehensive analysis aimed at proving the hypothesis that a train of small-scale features observed by the Wide-field Imager (WISPR) onboard the Parker Solar Probe (PSP) are the signature of a Kelvin–Helmholtz instability (KHI). These features were seen near the flank of a Coronal Mass Ejection (CME) wake between 7.5 R ⊙ and 9.5 R ⊙, lasting for about 30 minutes. The CME was a slow event, associated with a streamer blowout. We analyzed the size of the eddies and found growth during their evolution while maintaining separation distances and alignment typical of Kelvin–Helmholtz vortexes. We then assessed the magnetic field conditions that would make the observation of such an instability plausible. Two methods were used to cross-check our findings. The measured thickness of the boundary layer supports KHI candidacy, and the estimated linear growth rate suggests nonlinear saturation within the expected timescale. We conclude that a KHI is a plausible explanation for the observed features, and therefore that such instabilities might exist in the low and middle solar corona (within ∼15 R ⊙) and can be detected in white light observations. Their observation, however, might be rare due to stringent conditions like the observer's proximity, suitable viewing circumstances, magnetic field topology, and flow properties. This study highlights the unique capability of PSP/WISPR in observing such phenomena, especially as PSP perihelia reach closer distances to the Sun.

Keywords: the sun; solar corona; solar wind; solar coronal mass ejections; heliosphere
Can Galaxy Evolution Mimic Cosmic Reionization?

Lyα emitting galaxies are powerful tools to probe the late stages of cosmic reionization. The observed sudden drop in Lyα fraction at z > 6 is often interpreted as a sign of reionization, since the intergalactic medium (IGM) is more neutral and opaque to Lyα photons. Crucially, this interpretation of the observations is only valid under the assumption that galaxies themselves experience a minimal evolution at these epochs. By modeling Lyα radiative transfer effects in and around galaxies, we examine whether a change in the galactic properties can reproduce the observed drop in the Lyα fraction. We find that an increase in the galactic neutral hydrogen content or a reduction in the outflow velocity toward higher redshift both lead to a lower Lyα escape fraction, and can thus mimic an increasing neutral fraction of the IGM. We furthermore find that this change in galactic properties leads to systematically different Lyα spectra which can be used to differentiate the two competing effects. Using the CANDELSz7 survey measurements which indicate slightly broader lines at z ∼ 6, we find that the scenario of a mere increase in the galactic column density toward higher z is highly unlikely. We also show that a decrease in outflow velocity is not ruled out by existing data but leads to more prominent blue peaks at z > 6. Our results caution using Lyα observations to estimate the IGM neutral fraction without accounting for the potential change in the galactic properties, e.g., by mapping out the evolution of Lyα spectral characteristics.

Keywords: reionization; galaxy evolution; lyman-alpha galaxies; intergalactic medium; radiative transfer
The On-axis Jetted Tidal Disruption Event AT2022cmc: X-Ray Observations and Broadband Spectral Modeling

AT2022cmc was recently reported as the first on-axis jetted tidal disruption event (TDE) discovered in the last decade, and the fourth on-axis jetted TDE candidate known so far. In this work, we present NuSTAR hard X-ray (3–30 keV) observations of AT2022cmc, as well as soft X-ray (0.3–6 keV) observations obtained by NICER, Swift, and XMM-Newton. Our analysis reveals that the broadband X-ray spectra can be well described by a broken power law with f ν ∝ ν ‑0.5 (f ν ∝ ν ‑1) below (above) the rest-frame break energy of E bk ∼ 10 keV at the observer frame t obs = 7.8 and 17.6 days since discovery. At t obs = 36.2 days, the X-ray spectrum is consistent with either a single power law or a broken power law. By modeling the spectral energy distribution from radio to hard X-ray across the three NuSTAR observing epochs, we find that the submillimeter/radio emission originates from external shocks at large distances ≳1017 cm from the black hole, the UV/optical light comes from a thermal envelope with radius ∼1015 cm, and the X-ray emission is consistent with synchrotron radiation powered by energy dissipation at intermediate radii within the (likely magnetically dominated) jet. We constrain the bulk Lorentz factor of the jet to be of the order 10–100. Our interpretation differs from the model proposed by Pasham et al. where both the radio and X-rays come from the same emitting zone in a matter-dominated jet. Our model for the jet X-ray emission has broad implications on the nature of relativistic jets in other sources such as gamma-ray bursts.

Keywords: relativistic jets; tidal disruption; black hole physics; x-ray transient sources; supermassive black holes; high energy astrophysics
Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects. II

This is the second paper of a series presenting our search for magnetic cataclysmic variables (mCVs) among candidates selected mostly from the Catalina Real-Time Transient Survey. We present the identification spectra, obtained at the SOAR Telescope, as well as magnitudes and Gaia distances for 45 objects. Of these, 39 objects are identified as CVs, from which 8 targets show observational characteristics of mCVs, being 7 polars and 1 intermediate polar. The remaining 31 CVs in our sample are probably non-magnetic systems, in low (22 systems) or high (9 systems) accretion states. Six targets of the sample are not CVs (5 active galactic nuclei and 1 T Tauri star). Among the 8 objects with mCV spectra, 6 are new classifications. Three polars were observed in low-accretion state, either revealing photospheric features of the secondary star and allowing the estimation of their spectral type, or presenting Hβ Zeeman components associated to the white dwarf (WD) magnetic field. In addition to the results obtained in the first paper of the series, and depending on the confirmation of these classifications by observational follow-up, our results would increase the sample of known polars by about 9%.

Keywords: cataclysmic variable stars; dwarf novae; interacting binary stars; magnetic variable stars; am herculis stars; dq herculis stars; spectroscopy
Mapping Physical Conditions in Neighboring Hot Cores: NOEMA Studies of W3(H2O) and W3(OH)

The complex chemistry that occurs in star-forming regions can provide insight into the formation of prebiotic molecules at various evolutionary stages of star formation. To study this process, we present millimeter-wave interferometric observations of the neighboring hot cores W3(H2O) and W3(OH) carried out using the NOEMA interferometer. We have analyzed distributions of six molecules that account for most observed lines across both cores and have constructed physical parameter maps for rotational temperature, column density, and velocity field with corresponding uncertainties. We discuss the derived spatial distributions of these parameters in the context of the physical structure of the source. We propose the use of HCOOCH3 as a new temperature tracer in W3(H2O) and W3(OH) in addition to the more commonly used ${\mathrm{CH}}_{3}\mathrm{CN}$ . By analyzing the physically derived parameters for each molecule across both W3(H2O) and W3(OH), the work presented herein further demonstrates the impact of physical environment on hot cores at different evolutionary stages.

Keywords: astrochemistry; star forming regions; interferometry; h ii regions
Is Jet Re-orientation the Elusive Trigger for Star Formation Suppression in Radio Galaxies?

Jet re-orientation associated with the time evolution of radio quasars explains the formation of X-shaped radio galaxies and their preference for isolated environments. But since X-shaped radio galaxies are generally not found in dense environments (e.g., groups/clusters), the jet re-orientation phenomenon for radio galaxies in groups and clusters has been ignored. We take a closer look at the re-orientation of FRI jets with respect to FRII jets, and find that it may constitute the as-yet unidentified trigger for star formation suppression in radio galaxies. We show how the recently explored radio "red geyser" galaxies can be interpreted in this context and ultimately reveal a deeper understanding of why FRII radio galaxies are on one side of the star formation enhancement/suppression divide compared to FRI radio galaxies.

Keywords: star formation; relativistic jets
The Konus-Wind Catalog of Gamma-Ray Bursts with Known Redshifts. II. Waiting-Mode Bursts Simultaneously Detected by Swift/BAT

In the second part of The Konus-Wind Catalog of Gamma-Ray Bursts with Known Redshifts (the first part: Tsvetkova et al. 2017; T17), we present the results of a systematic study of gamma-ray bursts (GRBs) with reliable redshift estimates detected simultaneously by the Konus-Wind (KW) experiment (in the waiting mode) and by the Swift/BAT (BAT) telescope during the period from 2005 January to the end of 2018. By taking advantage of the high sensitivity of BAT and the wide spectral band of KW, we were able to constrain the peak spectral energies, the broadband energy fluences, and the peak fluxes for the joint KW-BAT sample of 167 weak, relatively soft GRBs (including four short bursts). Based on the GRB redshifts, which span the range 0.04 ≤ z ≤ 9.4, we estimate the rest frame, isotropic-equivalent energy, and peak luminosity. For 14 GRBs with reasonably constrained jet breaks, we provide the collimation-corrected values of the energetics. This work extends the sample of KW GRBs with known redshifts to 338 GRBs, the largest set of cosmological GRBs studied to date over a broad energy band. With the full KW sample, accounting for the instrumental bias, we explore GRB rest-frame properties, including hardness-intensity correlations, GRB luminosity evolution, luminosity and isotropic-energy functions, and the evolution of the GRB formation rate, which we find to be in general agreement with those reported in T17 and other previous studies.

Keywords: gamma-ray bursts
MUSUBI (MegaCam Ultra-deep Survey: u*-band Imaging) Data for the COSMOS and SXDS Fields

The Subaru Hyper Suprime-Cam (HSC) Strategic Survey is the latest-generation multiband optical imaging survey for galaxy evolution and structure formation. The "Ultra-deep" component of the HSC survey provides grizy broadband images over ~3.4 deg2 to detection limits of ~26-28 AB, along with narrowband images, in the COSMOS and SXDS fields. These images provide an unprecedented combination of depths and area coverage, for studies of galaxies up to z ~ 7. However, the lack of coverage at <4000 Å implies an incomplete sampling of the rest-frame UV at z ≲ 3, which is critically needed for understanding the buildup of stellar mass in later cosmic time. We conducted a multiyear CFHT u*-band imaging campaign in the two HSC Ultra-deep fields with CFHT MegaCam. By including shallower archival data, we reached 5σ depths of u* = 28.1 and 28.4 (AB) at the centers of the COSMOS and SXDS fields, respectively, and u* = 27.7 and 27.8 in the central 1 deg2 fields. The image quality is ≳ 0.″90, fairly good for the u* band. Both the photometric and astrometric quality of our data are excellent. We show that the combination of our u*-band and HSC data can lead to high-quality photometric redshifts at z = 0-3, and robust measurements of rest-frame UV on galaxies at 0.4 < z < 0.6 for distinguishing green-valley galaxies from star-forming and quiescent galaxies. We publicly release our reduced u*-band images and reference catalogs, which can be used readily for scientific studies.

Keywords: ultraviolet surveys; galaxy evolution; galaxy formation; high-redshift galaxies; astronomy databases; observational cosmology; green valley galaxies
Analytical and Numerical Studies of Central Galactic Outflows Powered by Tidal Disruption Events: A Model for the Fermi Bubbles?

Capture and tidal disruption of stars by the supermassive black hole in the Galactic center (GC) should occur regularly. The energy released and dissipated by these processes will affect both the ambient environment of the GC and the Galactic halo. The single star of a super-Eddington eruption generates a subsonic outflow with an energy release of more than 1052 erg, which still is not high enough to push shock heated gas into the halo. Only routine tidal disruption of stars near the GC can provide enough cumulative energy to form and maintain large-scale structures like the Fermi Bubbles. The average rate of disruption events is expected to be 10-4 ∼ 10-5 yr-1, providing the average power of energy release from the GC into the halo of $\dot{W}\sim 3\times {10}^{41}$ erg s-1, which is needed to support the Fermi Bubbles. The GC black hole is surrounded by molecular clouds in the disk, but their overall mass and filling factor are too low to significantly stall the shocks from tidal disruption events. The de facto continuous energy injection on timescales of megayears will lead to the propagation of strong shocks in a density stratified Galactic halo and thus create elongated bubble-like features that are symmetric to the Galactic midplane.

Keywords: galactic center; interstellar clouds; galactic winds; tidal disruption; superbubbles; gamma-rays; cosmic rays
Discovery of a Large-scale H I Plume in the NGC 7194 Group

We present the discovery of a new H I structure in the NGC 7194 group from the observations using the Karl G. Jansky Very Large Array. NGC 7194 group is a nearby (z ~ 0.027) small galaxy group with five quiescent members. The observations reveal a 200 kpc long H I plume that spans the entire group with a total mass of M H I = 3.4 × 1010 M ⊙. The line-of-sight velocity of the H I gas gradually increases from south (7200 km s-1) to north (8200 km s-1), and the local velocity dispersion is up to 70 km s-1. The structure is not spatially coincident with any member galaxies but it shows close associations with a number of blue star-forming knots. Intragroup H I gas is not rare, but this particular structure is still one of the unusual cases in the sense that it does not show any clear connection with sizable galaxies in the group. We discuss the potential origins of this large-scale H I gas in the NGC 7194 group and its relation with the intergalactic star-forming knots. We propose that this H I feature could have originated from tidal interactions among group members or the infall of a late-type galaxy into the group. Alternatively, it might be leftover gas from flyby intruders.

Keywords: neutral hydrogen clouds; galaxy groups; star forming regions
JWST Reveals Excess Cool Water near the Snow Line in Compact Disks, Consistent with Pebble Drift

Previous analyses of mid-infrared water spectra from young protoplanetary disks observed with the Spitzer-IRS found an anticorrelation between water luminosity and the millimeter dust disk radius observed with ALMA. This trend was suggested to be evidence for a fundamental process of inner disk water enrichment proposed decades ago to explain some properties of the solar system, in which icy pebbles drift inward from the outer disk and sublimate after crossing the snow line. Previous analyses of IRS water spectra, however, were uncertain due to the low spectral resolution that blended lines together. We present new JWST-MIRI spectra of four disks, two compact and two large with multiple radial gaps, selected to test the scenario that water vapor inside the snow line is regulated by pebble drift. The higher spectral resolving power of MIRI-MRS now yields water spectra that separate individual lines, tracing upper level energies from 900 to 10,000 K. These spectra clearly reveal excess emission in the low-energy lines in compact disks compared to large disks, demonstrating an enhanced cool component with T ≈ 170-400 K and equivalent emitting radius R eq ≈ 1-10 au. We interpret the cool water emission as ice sublimation and vapor diffusion near the snow line, suggesting that there is indeed a higher inward mass flux of icy pebbles in compact disks. Observation of this process opens up multiple exciting prospects to study planet formation chemistry in inner disks with JWST.

Keywords: protoplanetary disks; exoplanet formation; molecular spectroscopy; young stellar objects; classical t tauri stars; infrared spectroscopy; circumstellar disks; planet formation; star formation; pre-main sequence stars
Demographics of Hierarchical Black Hole Mergers in Dense Star Clusters

With about one hundred mergers of binary black holes (BBHs) detected via gravitational waves by the LIGO-Virgo-KAGRA (LVK) Collaboration, our understanding of the darkest objects in the universe has taken unparalleled steps forward. While most of the events are expected to consist of black holes (BHs) directly formed from the collapse of massive stars, some may contain the remnants of previous BBH mergers. In the most massive globular clusters and in nuclear star clusters, successive mergers can produce second- (2G) or higher-generation BHs, and even form intermediate-mass BHs (IMBHs). Overall, we predict that up to ~10%, ~1%, or ~0.1% of the BBH mergers have one component being a 2G, 3G, or 4G BH, respectively. Assuming that ~500 BBH mergers will be detected in O4 by LVK, this means that ~50, ~5, or ~0.5 events, respectively, will involve a 2G, 3G, or 4G BH, if most sources are produced dynamically in dense star clusters. With their distinctive signatures of higher masses and spins, such hierarchical mergers offer an unprecedented opportunity to learn about the BH populations in the densest stellar systems and to shed light on the elusive IMBHs that may form therein.

Keywords: astrophysical black holes; black holes; stellar mass black holes; intermediate-mass black holes; gravitational wave astronomy; gravitational wave detectors; gravitational wave sources; gravitational waves