adsabs/SciX_UAT_keywords huggingface dataset:
The Large Magellanic Cloud's 30 kpc Bow Shock and Its Impact on the Circumgalactic Medium

The interaction between the supersonic motion of the Large Magellanic Cloud (LMC) and the circumgalactic medium (CGM) is expected to result in a bow shock that leads the LMC's gaseous disk. In this letter, we use hydrodynamic simulations of the LMC's recent infall to predict the extent of this shock and its effect on the Milky Way's (MW) CGM. The simulations clearly predict the existence of an asymmetric shock with a present-day standoff radius of ~6.7 kpc and a transverse diameter of ~30 kpc. Over the past 500 Myr, ~8% of the MW's CGM in the southern hemisphere should have interacted with the shock front. This interaction may have had the effect of smoothing over inhomogeneities and increasing mixing in the MW CGM. We find observational evidence of the existence of the bow shock in recent Hα maps of the LMC, providing a potential explanation for the envelope of ionized gas surrounding the LMC. Furthermore, the interaction of the bow shock with the MW CGM may also explain the observations of ionized gas surrounding the Magellanic Stream. Using recent orbital histories of MW satellites, we find that many satellites have likely interacted with the LMC shock. Additionally, the dwarf galaxy Ret2 is currently sitting inside the shock, which may impact the interpretation of the reported gamma-ray excess in Ret2. This work highlights how bow shocks associated with infalling satellites are an underexplored yet potentially very important dynamical mixing process in the circumgalactic and intracluster media.

Keywords: large magellanic cloud; circumgalactic medium; hydrodynamical simulations
Hidden Companions to Nearby Intermediate-mass Stars. I. Discovery of a 0.82M ⊙, 15 au Companion to the Resolved 0.4 au Spectroscopic Binary in HIP 67199

Further discoveries and detailed studies of close binaries of intermediate-mass stars in hierarchical triple systems are needed in order to understand their formation. Here we report the discovery of a 0.82M ⊙ companion to the intermediate mass spectroscopic binary HIP 67199 at a projected separation of 150 mas ↔ 15 au based on a VLTI/GRAVITY observation. In addition, the spectroscopic binary was spatially resolved with a projected separation 1.70 mas ↔ 0.18 au and inferred masses 1.84M ⊙ + 1.72M ⊙. Further observations can determine the amplitude of eccentricity oscillations in the inner system induced by the third star. HIP 67199 is a potential progenitor for a double white dwarf hiding within the glow of a main-sequence companion. *Based on observations collected at the European Southern Observatory, Chile, Program ID 102.D-0817(C)

Keywords: multiple stars; a stars; optical interferometry
Intermittency and q-Gaussian Distributions in the Magnetic Field of the Very Local Interstellar Medium (VLISM) Observed by Voyager 1 and Voyager 2

Voyager 1 (V1) observed q-Gaussian distributions of 1 hr increments of the components the magnetic field ${\boldsymbol{B}}$ throughout the very local interstellar medium (VLISM) on scales on the order of 1 year, from 2013 through 2019, excluding the disturbed regions near two shocks. The intermittency of the components of B is described by q from the q-Gaussian distributions of 1 hr increments B as well as by the kurtosis K derived from the time series of the increments of ${\boldsymbol{B}}$ . Farther than ∼5 au from the heliopause, Voyager 1 observed larger intermittency in the fluctuations of the predominantly transverse component BN and in the nearly longitudinal component BT of ${\boldsymbol{B}}$ . The average values of q for the BN component and transverse BT component for these data in the VLISM are q = 1.32 ± 0.03 and q = 1.22 ± 0.03, respectively. The corresponding average values of the kurtosis are K = 7.2 and K = 4.9. Voyager 2 (V2) crossed the heliopause on 2018 November 5. Near the heliopause, in 2019, V2 observed large intermittency in 1 hr increments of the compressive component BT and smaller intermittency in BN. The Voyager 2 observations give q = 1.51 ± 0.06 and q = 1.17 ± 0.06 for the BN and BT components of B, respectively, as well as K = 7.2 and K = 12.3, respectively. The intermittency in BT and BN, observed by V2 near the heliopause was significantly larger than that observed by V1 when it was near the heliopause.

Keywords: interstellar medium; interstellar magnetic fields
Diffusive Shock Acceleration in N Dimensions

Collisionless shocks are often studied in two spatial dimensions (2D) to gain insights into the 3D case. We analyze diffusive shock acceleration for an arbitrary number $N\in {\mathbb{N}}$ of dimensions. For a nonrelativistic shock of compression ratio ${ \mathcal R }$ , the spectral index of the accelerated particles is ${s}_{{\rm{E}}}=1+N/({ \mathcal R }-1);$ this curiously yields, for any N, the familiar ${s}_{{\rm{E}}}=2$ (I.e., equal energy per logarithmic particle energy bin) for a strong shock in a monatomic gas. A precise relation between ${s}_{{\rm{E}}}$ and the anisotropy along an arbitrary relativistic shock is derived and is used to obtain an analytic expression for ${s}_{{\rm{E}}}$ in the case of isotropic angular diffusion, affirming an analogous result in 3D. In particular, this approach yields ${s}_{{\rm{E}}}=(1+\sqrt{13})/2\simeq 2.30$ in the ultrarelativistic shock limit for N = 2, and ${s}_{{\rm{E}}}(N\to \infty )=2$ for any strong shock. The angular eigenfunctions of the isotropic-diffusion transport equation reduce in 2D to elliptic cosine functions, providing a rigorous solution to the problem; the first function upstream already yields a remarkably accurate approximation. We show how these and additional results can be used to promote the study of shocks in 3D.

Keywords: high energy astrophysics; shocks; magnetic fields; cosmic rays
Exploring Low-mass Black Holes through Tidal Disruption Events in the Early Universe: Perspectives in the Era of the JWST, Roman Space Telescope, and LSST Surveys

The James Webb Space Telescope (JWST) has recently uncovered the presence of low-luminosity active galactic nuclei (AGNs) at z = 4–11. Spectroscopic observations have provided estimates of the nuclear black hole (BH) masses for these sources, extending the low-mass boundary down to M • ∼ 106–7 M ⊙. Despite this breakthrough, the observed lowest mass of BHs is still ≳1–2 orders of magnitude heavier than the predicted mass range of their seed population, thereby leaving the initial mass distribution of massive BHs poorly constrained. In this paper, we focus on UV-to-optical (in the rest frame) flares of stellar tidal disruption events (TDEs) embedded in low-luminosity AGNs as a tool for exploring low-mass BH populations with ≲104–6 M ⊙. We provide an estimate of the TDE rate over z = 4–11, associated with the properties of JWST-detected AGN host galaxies, and we find that deep and wide survey programs with JWST and the Roman Space Telescope (RST) can detect and identify TDEs up to z ≃ 4–7. The predicted detection numbers of TDEs at z > 4 in 1 yr are ${{ \mathcal N }}_{\mathrm{TDE}}\sim 2\mbox{--}10\,(0.2\mbox{--}2)$ for the JADES-Medium (and COSMOS-Web) survey with JWST and ${{ \mathcal N }}_{\mathrm{TDE}}\sim 2\mbox{--}10\,(8\mbox{--}50)$ for the deep (and wide) tiers of the High Latitude Time Domain Survey with RST. We further discuss survey strategies for hunting for transient high-redshift TDEs in wide-field surveys with RST, as well as a joint observation campaign with the Vera C. Rubin Observatory for enhancing the detection number. The high-redshift TDE search will give us a unique opportunity to probe the mass distribution of early BH populations.

Keywords: supermassive black holes; quasars; galaxy formation; high-redshift galaxies; tidal disruption
Characteristic Timescales for the Dayside Martian Ionosphere: Chemistry, Diffusion, and Magnetization

Different boundaries could be defined in a planetary ionosphere where the dominant process in function switches from one to the other. Identifying these boundaries and understanding their variations are hence crucial for disentangling the complexity of the ionosphere. Focusing on Mars, we perform a data-driven analysis of various boundaries and the associated time constants based on the multi-instrument measurements made by the Mars Atmosphere and Volatile Evolution mission during six campaigns that sample broadly different internal and external conditions. The boundaries we investigate include the photochemical equilibrium (PCE) boundary, the magnetic frozen boundary, the ion collision boundary, and the ion gyration boundary. Our analysis reveals systematic solar cycle and diurnal variations in that all boundaries tend to be elevated at enhanced solar activity and on the dayside and duskside of Mars. The variations with the magnetic environment are not observed for all boundaries except for the PCE boundary that exhibits an obvious elevation in strongly magnetized regions. Finally, our analysis suggests interesting species-dependent variations of different boundaries. In particularly, the PCE boundary shows the largest variability among all, with reduced boundary locations for all terminal species (NO+, HCO+, ${{\rm{O}}}_{2}^{+}$ , and H3O+) and one extra nonterminal species (CO2 +) owing to different chemical properties rendered by different ions.

Keywords: planetary ionospheres; solar-planetary interactions; mars
AGN STORM 2. V. Anomalous Behavior of the C IV Light Curve of Mrk 817

An intensive reverberation mapping campaign of the Seyfert 1 galaxy Mrk 817 using the Cosmic Origins Spectrograph on the Hubble Space Telescope revealed significant variations in the response of broad UV emission lines to fluctuations in the continuum emission. The response of the prominent UV emission lines changes over an ∼60 day duration, resulting in distinctly different time lags in the various segments of the light curve over the 14 month observing campaign. One-dimensional echo-mapping models fit these variations if a slowly varying background is included for each emission line. These variations are more evident in the C IV light curve, which is the line least affected by intrinsic absorption in Mrk 817 and least blended with neighboring emission lines. We identify five temporal windows with a distinct emission-line response, and measure their corresponding time delays, which range from 2 to 13 days. These temporal windows are plausibly linked to changes in the UV and X-ray obscuration occurring during these same intervals. The shortest time lags occur during periods with diminishing obscuration, whereas the longest lags occur during periods with rising obscuration. We propose that the obscuring outflow shields the broad UV lines from the ionizing continuum. The resulting change in the spectral energy distribution of the ionizing continuum, as seen by clouds at a range of distances from the nucleus, is responsible for the changes in the line response. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program GO-16196.

Keywords: active galaxies; active galactic nuclei; seyfert galaxies; galaxy nuclei
The Accurate Mass Distribution of M87, the Giant Galaxy with Imaged Shadow of Its Supermassive Black Hole, as a Portal to New Physics

The very careful Event Horizon Telescope estimate of the mass of the supermassive black hole at the center of the giant cD galaxy M87, allied with recent high-quality photometric and spectroscopic measurements, yields a proper dark/luminous mass decomposition from the galaxy center to its virial radius. That provides us with decisive information on crucial cosmological and astrophysical issues. The dark and the standard matter distributions in a wide first time detected galaxy region under the supermassive black hole gravitational control. The well-known supermassive black hole mass versus stellar dispersion velocity relationship at the highest galaxy masses implies an exotic growth of the former. This may be the first case in which one can argue that the supermassive black hole mass growth was also contributed by the dark matter component. A huge dark matter halo core in a galaxy with inefficient baryonic feedback is present and consequently constrains the nature of the dark halo particles. The unexplained entanglement between dark/luminous structural properties, already emerged in disk systems, also appears.

Keywords: dark matter distribution; supermassive black holes; dark matter
Star-forming Clumps in Local Luminous Infrared Galaxies

We present HST narrowband near-infrared imaging of Paα and Paβ emission of 48 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey. These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extranuclear clumps) and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs the star-forming clumps have radii ranging from ∼90 to 900 pc and star formation rates (SFRs) of ∼1 × 10-3 to 10 M⊙ yr-1, with median values for extranuclear clumps of 170 pc and 0.03 M⊙ yr-1. The detected star-forming clumps are young, with a median stellar age of 8.7 Myr, and have a median stellar mass of 5 × 105 M⊙. The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at z = 1-3. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10% to 90%. If local LIRGs are similar to these simulated galaxies, we expect that future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs.

Keywords: interacting galaxies; star forming regions; luminous infrared galaxies
Shear Measurement with Poorly Resolved Images

Weak lensing studies typically require excellent seeing conditions for the purpose of maximizing the number density of well-resolved galaxy images. It is interesting to ask to what extent the seeing size limits the usefulness of the astronomical images in weak lensing. In this work, we study this issue with the data of the DECam Legacy Survey, which is a part of the target selection program for the Dark Energy Spectroscopic Instrument. Using the Fourier_Quad shear measurement pipeline, we demonstrate that images with relatively poor seeing conditions (~1.″5) can still yield accurate shear estimators. We do not find any correlation between systematic shear error and the image resolution.

Keywords: gravitational lensing; gravitational lensing shear; weak gravitational lensing
Distribution of Merging and Post-merger Galaxies in Nearby Galaxy Clusters

We study the incidence and spatial distribution of galaxies that are currently undergoing gravitational merging (M) or that have signs of being post-merger (PM) in six galaxy clusters (A754, A2399, A2670, A3558, A3562, and A3716) within the redshift range of 0.05 ≲ z ≲0.08. To this aim, we obtained Dark Energy Camera mosaics in the ${u}^{{\prime} }$ , ${g}^{{\prime} }$ , and ${r}^{{\prime} }$ bands covering up to 3 × R 200 of the clusters, reaching 28 mag arcsec‑2 surface brightness limits. We visually inspect ${u}^{{\prime} }$ ${g}^{{\prime} }$ ${r}^{{\prime} }$ color-composite images of volume-limited (M r < ‑20) cluster member galaxies to identify whether galaxies are of M or PM type. We find 4% M-type and 7% PM-type galaxies in the galaxy clusters studied. By adding spectroscopic data and studying the projected phase-space diagram (PPSD) of the projected clustocentric radius and the line-of-sight velocity, we find that PM-type galaxies are more virialized than M-type galaxies, having a 1%–5% higher fraction within the escape-velocity region, while the fraction of M-type was ∼10% higher than the PM type in the intermediate environment. Similarly, on a substructure analysis, M types were found in groups in the outskirts, while PM-type populated groups were found in ubiquitous regions of the PPSD. Adopting literature-derived dynamical state indicator values, we observed a higher abundance of M types in dynamically relaxed clusters. This finding suggests that galaxies displaying post-merger features within clusters likely merged in low-velocity environments, including clusters outskirts and dynamically relaxed clusters.

Keywords: abell clusters; galaxy clusters; galaxy mergers; interacting galaxies; galaxy evolution
Candidate z ∼ 2.5 Lyman Continuum Sources in the GOODS Fields

We use the wealth of deep archival optical spectroscopy on the GOODS-South field from Keck, the VLT, and other facilities to select candidate high-redshift Lyman continuum (LyC) leakers in the Hubble Deep UV Legacy Survey (HDUV) data set. We select sources at $2.35\lt z\lt 3.05$ , where the HST/WFC3 F275W filter probes only the redshifted LyC. We find five moderately F275W-bright sources (four detected at $\gtrsim 3\sigma $ significance) in this redshift range. However, two of these show evidence in their optical spectra of contamination by foreground galaxies along the line of sight. We then perform an F275W error-weighted sum of the fluxes of all 129 galaxies at $2.35\lt z\lt 3.05$ in both the GOODS-N and GOODS-S HDUV areas to estimate the total ionizing flux. The result is dominated by just five candidate F275W-bright LyC sources. Lastly, we examine the contributions to the metagalactic ionizing background, finding that, at the sensitivity of the HDUV F275W data and allowing for the effects of LyC transmission in the intergalactic medium (IGM), star-forming galaxies can match the UV flux required to maintain an ionized IGM at $z\sim 2.5$ .

Keywords: high-redshift galaxies; galaxy evolution; observational cosmology; galaxy formation; galaxy distances; active galaxies
Orbital Dynamics Landscape near the Most Distant Known Trans-Neptunian Objects

The most distant known trans-Neptunian objects (TNOs), those with perihelion distance above 38 au and semimajor axis above 150 au, are of interest for their potential to reveal past, external, or present but unseen perturbers. Realizing this potential requires understanding how the known planets influence their orbital dynamics. We use a recently developed Poincaré mapping approach for orbital phase space studies of the circular planar restricted three-body problem, which we have extended to the case of the 3D restricted problem with N planetary perturbers. With this approach, we explore the dynamical landscape of the 23 most distant TNOs under the perturbations of the known giant planets. We find that, counter to common expectations, almost none of these TNOs are far removed from Neptune's resonances. Nearly half (11) of these TNOs have orbits consistent with stable libration in Neptune's resonances; in particular, the orbits of TNOs 148209 and 474640 overlap with Neptune's 20:1 and 36:1 resonances, respectively. Five objects can be ruled currently nonresonant, despite their large orbital uncertainties, because our mapping approach determines the resonance boundaries in angular phase space in addition to semimajor axis. Only three objects are in orbital regions not appreciably affected by resonances: Sedna, 2012 VP113 and 2015 KG163. Our analysis also demonstrates that Neptune's resonances impart a modest (few percent) nonuniformity in the longitude of perihelion distribution of the currently observable distant TNOs. While not large enough to explain the observed clustering, this small dynamical sculpting of the perihelion longitudes could become relevant for future, larger TNO data sets.

Keywords: trans-neptunian objects; kuiper belt; detached objects; resonant kuiper belt objects; celestial mechanics; orbital resonances
Crustal Magnetic Fields Do Not Lead to Large Magnetic-field Amplifications in Binary Neutron Star Mergers

The amplification of magnetic fields plays an important role in explaining numerous astrophysical phenomena associated with binary neutron star mergers, such as mass ejection and the powering of short gamma-ray bursts. Magnetic fields in isolated neutron stars are often assumed to be confined to a small region near the stellar surface, while they are normally taken to fill the whole star in numerical modeling of mergers. By performing high-resolution, global, and high-order general-relativistic magnetohydrodynamic simulations, we investigate the impact of a purely crustal magnetic field and contrast it with the standard configuration consisting of a dipolar magnetic field with the same magnetic energy but filling the whole star. While the crust configurations are very effective in generating strong magnetic fields during the Kelvin-Helmholtz-instability stage, they fail to achieve the same level of magnetic-field amplification of the full-star configurations. This is due to the lack of magnetized material in the neutron-star interiors to be used for further turbulent amplification and to the surface losses of highly magnetized matter in the crust configurations. Hence, the final magnetic energies in the two configurations differ by more than 1 order of magnitude. We briefly discuss the impact of these results on astrophysical observables and how they can be employed to deduce the magnetic topology in merging binaries.

Keywords: neutron stars; magnetars; magnetic fields; magnetohydrodynamical simulations; magnetohydrodynamics
Are There Transit Timing Variations for the Exoplanet Qatar-1b?

Motivated by the unsettled conclusion on whether there are any transit timing variations (TTVs) for the exoplanet Qatar-1b, 10 new transit light curves are presented and a TTV analysis with a baseline of 1400 epochs is performed. Because the linear model provides a good fit with a reduced chi-square of ${\chi }_{\mathrm{red}}^{2}=2.59$ and the false-alarm probabilities of the possible TTV frequencies are as large as 35%, our results are consistent with a null-TTV model. Nevertheless, a new ephemeris with a reference time of T0 = 2455647.63360 ± 0.00008 (BJD) and a period of P = 1.4200236 ± 0.0000001 (day) is obtained. In addition, the updated orbital semimajor axis and planetary radius in units of stellar radius are provided, and the lower limit of the modified stellar tidal quality factor is also determined.

Keywords: exoplanet astronomy; transit photometry