adsabs/SciX_UAT_keywords huggingface dataset:
Probing the Cold Neutral Medium through H I Emission Morphology with the Scattering Transform

Neutral hydrogen (H I) emission exhibits complex morphology that encodes rich information about the physics of the interstellar medium. We apply the scattering transform (ST) to characterize the H I emission structure via a set of compact and interpretable coefficients, and find a connection between the H I emission morphology and H I cold neutral medium (CNM) phase content. Where H I absorption measurements are unavailable, the H I phase structure is typically estimated from the emission via spectral line decomposition. Here, we present a new probe of the CNM content using measures that are solely derived from H I emission spatial information. We apply the ST to GALFA-H I data at high Galactic latitudes ( $\left|b\right|\gt 30^\circ $ ), and compare the resulting coefficients to CNM fraction measurements derived from archival H I emission and absorption spectra. We quantify the correlation between the ST coefficients and the measured CNM fraction (f CNM), finding that the H I emission morphology encodes substantial f CNM-correlating information and that ST-based metrics for small-scale linearity are particularly predictive of f CNM. This is further corroborated by the enhancement of the I 857/N HI ratio with larger ST measures of small-scale linearity. These results are consistent with the picture of regions with higher CNM content being more populated by small-scale filamentary H I structures. Our work illustrates a physical connection between the H I morphology and phase content, and suggests that future phase decomposition methods can be improved by making use of both H I spectral and spatial information.

Keywords: interstellar medium; cold neutral medium; h i line emission; astrostatistics; wavelet analysis
TXS 0128+554: A Young Gamma-Ray-emitting Active Galactic Nucleus with Episodic Jet Activity

We have carried out a Chandra X-ray and multifrequency radio Very Long Baseline Array study of the active galactic nucleus (AGN) TXS 0128+554, which is associated with the Fermi γ-ray source 4FGL J0131.2+5547. The AGN is unresolved in a target 19.3 ks Chandra image, and its spectrum is well fit by a simple absorbed power-law model, with no distinguishable spectral features. Its relatively soft X-ray spectrum compared to other compact symmetric objects (CSOs) may be indicative of a thermal emission component, for which we were able to obtain an upper temperature limit of kT = 0.08 keV. The compact radio morphology and measured advance speed of 0.32 c ± 0.07 c indicate a kinematic age of only 82 yr ± 17 yr, placing TXS 0128+554 among the youngest members of the CSO class. The lack of compact, inverted spectrum hotspots and an emission gap between the bright inner jet and outer radio lobe structure indicate that the jets have undergone episodic activity, and were relaunched a decade ago. The predicted γ-ray emission from the lobes, based on an inverse Compton-emitting cocoon model, is three orders of magnitude below the observed Fermi-LAT flux. A comparison to other Fermi-detected and non-Fermi-detected CSOs with redshift z < 0.1 indicates that the γ-ray emission likely originates in the inner jet/core region, and that nearby, recently launched AGN jets are primary candidates for detection by the Fermi-LAT instrument.

Keywords: x-ray active galactic nuclei; radio jets; active galactic nuclei; jets; relativistic jets; gamma-ray astronomy; radio galaxies; radio lobes; extragalactic radio sources; very long baseline interferometry
Magnetic-buoyancy-induced Mixing in AGB Stars: Presolar SiC Grains

Isotope ratios can be measured in presolar SiC grains from ancient asymptotic giant branch (AGB) stars at permil-level (0.1%) precision. Such precise grain data permit derivation of more stringent constraints and calibrations on mixing efficiency in AGB models than traditional spectroscopic observations. In this paper we compare SiC heavy-element isotope ratios to a new series of FRUITY models that include the effects of mixing triggered by magnetic fields. Based on 2D and 3D simulations available in the literature, we propose a new formulation, upon which the general features of mixing induced by magnetic fields can be derived. The efficiency of such a mixing, on the other hand, relies on physical quantities whose values are poorly constrained. We present here our calibration by comparing our model results with the heavy-element isotope data of presolar SiC grains from AGB stars. We demonstrate that the isotopic compositions of all measured elements (Ni, Sr, Zr, Mo, Ba) can be simultaneously fitted by adopting a single magnetic field configuration in our new FRUITY models.

Keywords: circumstellar dust; stellar abundances; stellar magnetic fields; asymptotic giant branch stars; stellar rotation; chemically peculiar stars; magnetohydrodynamics
Characteristics of Electron Pitch-angle Distribution in the Flapping Magnetotail

The configuration, local motions, and related physics processes of the terrestrial magnetotail have been well studied, playing a key role in magnetotail dynamics. But characteristics of electron pitch-angle distribution (PAD), and the formation mechanisms, at different regions in the flapping magnetotail were not pointed out. Here, we study a current sheet crossing event detected by the Magnetospheric Multiscale Mission inside a magnetotail, and investigate the electron PAD of the event in detail. When the spacecraft are out of the current sheet, low-energy and high-energy electrons present field-aligned PAD and cigar-type PAD, respectively. This difference shows different motions of electrons. We proposed two possible explanation mechanisms: crossing a newly dipolarized magnetotail, or crossing the exhaust region of the reconnection region, and we discussed them in the paper adequately. Based on the dipolarized mechanism, for the first time, we point out that bouncing electrons could be the indicator of a newly dipolarized magnetotail. In addition, four other current sheet crossing cases with similar signatures are observed. Our study improves the understanding of current sheet dynamics and magnetotail configuration physics.

Keywords: magnetic fields; planetary magnetospheres; space plasmas; plasma physics
Formation of a Magnetic Cloud from the Merging of Two Successive Coronal Mass Ejections

On 2022 March 28 two successive coronal mass ejections (CMEs) were observed by multiple spacecraft and resulted in a magnetic cloud (MC) at 1 au. We investigate the propagation and interaction properties of the two CMEs correlated with the MC using coordinated multipoint remote sensing and in situ observations from Solar Orbiter, STEREO-A, Solar and Heliospheric Observatory, and Wind. The first CME was triggered by a filament eruption with a high inclination angle. Roughly 9 hr later, the second CME originating from the same active region erupted with a smaller tilt angle and faster speed compared to the first one. The second CME overtook the preceding CME and formed a merged front at approximately 75 R ☉, which developed into a complex ejecta at 1 au. The descending speed and low proton temperature inside the complex ejecta suggest that the two CMEs have fully merged before reaching 1 au, leading them to begin expanding rather than compressing against each other. The complex ejecta appears to have the magnetic field and plasma signatures of an MC, although there is a discontinuity in the magnetic field implying previous interactions. The cross section of the complex ejecta, reconstructed from in situ data using a Grad–Shafranov technique, exhibits a right-handed flux rope structure. These results highlight that an MC-like complex ejecta lacking interaction features could arise from the complete merging of two CMEs.

Keywords: solar coronal mass ejections; solar-terrestrial interactions; solar wind
Global Simulations of the Vertical Shear Instability with Nonideal Magnetohydrodynamic Effects

The mechanisms of angular momentum transport and the level of turbulence in protoplanetary disks (PPDs) are crucial for understanding many aspects of planet formation. In recent years, it has been realized that the magneto-rotational instability tends to be suppressed in PPDs due to nonideal magnetohydrodynamic (MHD) effects, and the disk is primarily laminar with accretion driven by magnetized disk winds. In parallel, several hydrodynamic mechanisms have been identified that likely also generate vigorous turbulence and drive disk accretion. In this work, we study the interplay between MHD winds in PPDs with the vertical shear instability (VSI), one of the most promising hydrodynamic mechanisms, through 2D global nonideal MHD simulations with ambipolar diffusion (AD) and ohmic resistivity. For typical disk parameters, MHD winds can coexist with the VSI with accretion primarily wind-driven accompanied by vigorous VSI turbulence. The properties of the VSI remain similar to the unmagnetized case. The wind and overall field configuration are not strongly affected by the VSI turbulence, showing a modest level of variability and corrugation of the midplane current sheet. Weak AD strength or the enhanced coupling between gas and magnetic fields weakens the VSI. The VSI is also weakened with increasing magnetization, and characteristic VSI corrugation modes transition to low-amplitude breathing mode oscillations with strong magnetic fields.

Keywords: protoplanetary disks; magnetohydrodynamics; astrophysical fluid dynamics
EMPRESS. VI. Outflows Investigated in Low-mass Galaxies with M ∗ = 104-107 M ⊙: Weak Feedback in Low-mass Galaxies?

We study emission line profiles of 21 nearby low-mass (M * = 104-107 M ⊙) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These low-mass galaxies are actively star-forming systems with high specific star formation rates of ~100-1000 Gyr-1 that are well above the star formation main sequence and its extrapolation. We identify broad-line components of Hα and [O III]λ5007 emission in 14 out of the 21 galaxies that cannot be explained by the MagE instrumental profile or the natural broadening of line emission. We conduct double-Gaussian profile fitting to the emission of the 14 galaxies, and find that the broad-line components have line widths significantly larger than those of the narrow-line components, indicative of galactic outflows. The broad-line components have moderately large line widths of ~100 km s-1. We estimate the maximum outflow velocities v max and obtain values of ≃60-200 km s-1, which are found to be comparable to or slightly larger than the escape velocities. Positive correlations of v max with star formation rates, stellar masses, and circular velocities extend down into this low-mass regime. Broad- to narrow-line flux ratios (BNRs) are generally found to be smaller than those of massive galaxies. The small v max and BNRs suggest that the mass-loading factors η can be as small as 0.1-1 or below, in contrast to the large η of energy-driven outflows predicted by numerical simulations.

Keywords: dwarf galaxies; galaxy winds; stellar feedback; galaxy evolution
The GBT Diffuse Ionized Gas Survey (GDIGS): Survey Overview and First Data Release

The Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) traces ionized gas in the Galactic midplane by measuring 4-8 GHz radio recombination line (RRL) emission. The nominal survey zone is 32°3 > ℓ > - 5°, ∣b∣ < 0°5, but coverage extends above and below the plane in select fields and additionally includes the areas around W47 (ℓ ≃ 37°5) and W49 (ℓ ≃ 43°). GDIGS simultaneously observes 22 Hnα (15 usable), 25 Hnβ (18 usable), and 8 Hnγ RRLs (all usable), as well as multiple molecular line transitions (including those of ${{\rm{H}}}_{2}^{13}\mathrm{CO}$ , H2CO, and CH3OH). Here, we describe the GDIGS survey parameters and characterize the RRL data, focusing primarily on the Hnα data. We produce sensitive data cubes by averaging the usable RRLs, after first smoothing to a common spectral resolution of 0.5 km s-1 and a spatial resolution of 2'65 for Hnα, 2'62 for Hnβ, and 2'09 for Hnγ. The average spectral noise per spaxel in the Hnα data cubes is ∼10 mK (∼5 mJy beam-1). This sensitivity allows GDIGS to detect RRLs from plasma throughout the inner Galaxy. The GDIGS Hnα data are sensitive to emission measures EM ≳ 1100 cm-6 pc, which corresponds to a mean electron density <ne> ≳ 30 cm-3 for a 1 pc path length or <ne> ≳ 1 cm-3 for a 1 kpc path length.

Keywords: warm ionized medium; interstellar plasma; h ii regions; interstellar line emission
Two-injection Scenario for the Hard X-Ray Excess Observed in Mrk 421

An interesting result that was recently reported for Mrk 421 is the detection of a significant excess at hard X-ray energies, which could provide useful information to investigate particle acceleration and emission mechanisms in the relativistic jet. Considering a two-injection scenario, we develop a self-consistent one-zone leptonic model to understand the origin of the hard X-ray excess in Mrk 421 during the period of extremely low X-ray and very high-energy flux in 2013 January. In the model, two populations of mono-energetic ultra-relativistic electrons are injected into the emission region, which is a magnetized plasmoid propagating along the blazar jet. We numerically calculate the emitting electron energy distribution by solving a kinetic equation that incorporates both shock acceleration and stochastic acceleration processes. Moreover, we infer analytic expressions relating the electrons' acceleration, cooling, escape, and injection to the observed spectra and variability. In particular, for the injection luminosity, we derive a new approximate analytical expression for the case of continual injection with a mono-energetic distribution. Based on a comparison between the theoretical predictions and the observed SED, we conclude that the hard X-ray excess that was observed in Mrk 421 may be due to the synchrotron radiation emitted by an additional electron population, which is co-spatial with an electron population producing simultaneous optical/UV, soft X-ray, and γ-ray emissions. Therefore, stochastic acceleration may play a major role in producing the observed X-ray spectrum.

Keywords: bl lacertae objects
Recovery of High-energy Low-frequency Quasiperiodic Oscillations from Black Hole X-Ray Binary MAXI J1535–571 with a Hilbert–Huang Transform Method

We propose a method based on the Hilbert–Huang transform (HHT) to recover the high-energy waveform of low-frequency quasiperiodic oscillations (QPOs). Based on the method, we successfully obtain the modulation of the phase-folded light curve above 170 keV using the QPO phase reconstructed at lower energies in MAXI J1535–571 with Insight-HXMT observations. A comprehensive simulation study is conducted to demonstrate that such modulation indeed originates from the QPO. Thus, the highest energies turn out to significantly exceed the upper limit of ∼100 keV for QPOs reported previously using the Fourier method, marking the first opportunity to study QPO properties above 100 keV in this source. Detailed analyses of these high-energy QPO profiles reveal different QPO properties between the 30–100 and 100–200 keV energy ranges: the phase lag remains relatively stable, and the amplitude slightly increases below ∼100 keV, whereas above this threshold, soft phase lags and a decrease in amplitude are observed. Given the reports of a hard-tail detection in broad spectroscopy, we propose that the newly discovered QPO properties above 100 keV are dominated by the hard-tail component, possibly stemming from a relativistic jet. Our findings also indicate a strong correlation between the QPOs originating from the jet and corona, supporting the scenario of jet–corona coupling precession. We emphasize that our proposed HHT-based method can serve as an efficient manner in expanding the high-energy band for studying QPOs, thereby enhancing our understanding of their origin.

Keywords: accretion; black hole physics; x-ray binary stars
The Effect of Chemisorption on the Chemical Evolution of Star-forming Regions

We have studied the production of simple molecules on interstellar dust grains involving strong bonding via chemisorption on a graphite surface. Two classes of chemical simulations were run: models under isothermal conditions at temperatures from 150 to 400 K at 25 K intervals, and warm-up models starting at 10 K. For the isothermal models, physisorption does not occur appreciably, whereas for the warm-up models, it dominates at the lower temperatures before thermal desorption becomes rapid. We have made several simple approximations to determine what role, if any, chemisorption can play in the surface chemistry that occurs at temperatures above which icy mantles no longer cover the surface of dust grains. Our major finding is that the importance of chemisorption is greatly dependent on the efficiency of adsorption. Models having the lowest adsorption barrier show maximum abundances of chemisorbed species. Species such as CO, which are very efficiently formed in the gas phase at almost all temperatures (10-400 K), will not be strongly impacted by the existence of chemisorbed species. However, chemisorbed CO can achieve a reasonably high abundance (∼10-6). Species such as C2H2 and NH3, which are less efficiently formed compared with CO in the gas phase, may show a change in their gas-phase abundance due to chemisorption. Several examples of this class of species can also show reasonably high abundances on grain surfaces due to chemisorption when the adsorption barrier is low.

Keywords: astrochemistry; interstellar medium; interstellar molecules; molecule formation; interstellar dust
The Ionized- and Cool-gas Content of the BR1202-0725 System as Seen by MUSE and ALMA

We present Multi Unit Spectroscopic Explorer (MUSE) observations of the gas-rich major merger BR1202-0725 at z ∼ 4.7, which constitutes one of the most overdense fields known in the early universe. We utilize these data in conjunction with existing Atacama Large Millimeter/submillimeter Array (ALMA) observations to compare and contrast the spatially resolved ionized- and cool-gas content of this system, which hosts a quasar (QSO), a submillimeter galaxy (SMG), the two known optical companion Lyα emitters ("LAE 1" and "LAE 2"), and an additional companion discovered in this work "LAE 3" just 5″ to the north of the QSO. We find that QSO BR1202-0725 exhibits a large Lyα halo, covering ≈55 pkpc on-sky at surface-brightness levels of SB ≥ 1 × 10-17 erg s-1 cm-2 arcsec-2. In contrast, the SMG, of similar far-infrared luminosity and star formation rate (SFR), does not exhibit such a Lyα halo. The QSO's halo exhibits high velocity widths (∼1000 km s-1) but the gas motion is to some extent kinematically coupled with the previously observed [C II] bridge between the QSO and the SMG. We note that the object known in the literature as LAE 2 shows no local peak of Lyα emission, rather, its profile is more consistent with being part of the QSO's extended Lyα halo. The properties of LAE 3 are typical of high-redshift LAEs; we measure FLyα(LAE 3) = 0.24 ± 0.03 × 10-16 erg s-1 cm-2, corresponding to SFRLyα ≈ 5.0 ± 0.5 M⊙ yr-1. The velocity width is Δv(LAE 3) ≈ 400 km s-1, and the equivalent width is EW0( $\mathrm{Ly}{\alpha }_{5\sigma }^{\mathrm{lim}})\geqslant 34.05$ Å, consistent with star formation being the primary driver of Lyα emission. We also note a coherent absorption feature at ∼-400 km s-1 in spectra from at least three objects; the QSO, LAE 1, and LAE 2, which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.

Keywords: broad-absorption line quasar; quasars
70 Years of Chromospheric Solar Activity and Dynamics

From 1915 to 1985 the monitoring program of the Mount Wilson Observatory, one of the Observatories of the Carnegie Institution of Washington, has taken over 35,000 daily images (spectroheliograms) of the Sun in the chromospheric resonance line of Ca II K. This important database constitutes a unique resource for a variety of retrospective analyses of the state of solar magnetism on multidecadal timescales. These observations may also hold the key for untangling some of the mysteries behind the solar dynamo, which in turn could result in a better predictive capability for current dynamo models. We describe here a procedure to calibrate and rescale these images so that homogeneous Carrington synoptic maps can be derived for the whole period covered by these observations. Temporal variations in full-disk chromospheric activity clearly show the signature of the 11 yr solar cycle, but no evidence is found for a statistically significant north/south hemispheric asymmetry. Using a feature-tracking technique we were also able to obtain the average solar rotation profile. We find no indication of any detectable periodicity in the temporal behavior of the orthogonalized rotation rate coefficients, suggesting the global chromospheric dynamics has not changed during the 70 years investigated in this work. We found also no significant evidence in our analysis for a hemispheric asymmetry in rotation rates.

Keywords: solar activity
Relating Streamer Flows to Density and Magnetic Structures at the Parker Solar Probe

The physical mechanisms that produce the slow solar wind are still highly debated. Parker Solar Probe's (PSP's) second solar encounter provided a new opportunity to relate in situ measurements of the nascent slow solar wind with white-light images of streamer flows. We exploit data taken by the Solar and Heliospheric Observatory, the Solar TErrestrial RElations Observatory (STEREO), and the Wide Imager on Solar Probe to reveal for the first time a close link between imaged streamer flows and the high-density plasma measured by the Solar Wind Electrons Alphas and Protons (SWEAP) experiment. We identify different types of slow winds measured by PSP that we relate to the spacecraft's magnetic connectivity (or not) to streamer flows. SWEAP measured high-density and highly variable plasma when PSP was well connected to streamers but more tenuous wind with much weaker density variations when it exited streamer flows. STEREO imaging of the release and propagation of small transients from the Sun to PSP reveals that the spacecraft was continually impacted by the southern edge of streamer transients. The impact of specific density structures is marked by a higher occurrence of magnetic field reversals measured by the FIELDS magnetometers. Magnetic reversals are associated with much stronger density variations inside than outside streamer flows. We tentatively interpret these findings in terms of magnetic reconnection between open magnetic fields and coronal loops with different properties, providing support for the formation of a subset of the slow wind by magnetic reconnection.

Keywords: slow solar wind; solar coronal streamers; solar coronal transients