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<jats:title>Abstract</jats:title> <jats:p>We study the stellar and gas kinematics of the brightest group galaxies (BGGs) in dynamically relaxed and unrelaxed galaxy groups for a sample of 154 galaxies in the SAMI galaxy survey. We characterize the dynamical state of the groups using the luminosity gap between the two most luminous galaxies and the BGG offset from the luminosity centroid of the group. We find that the misalignment between the rotation axis of gas and stellar components is more frequent in the BGGs in unrelaxed groups, although with quite low statistical significance. Meanwhile, galaxies whose stellar dynamics would be classified as “regular rotators” based on their kinemetry are more common in relaxed groups. We confirm that this dependency on group dynamical state remains valid at fixed stellar mass and Sérsic index. The observed trend could potentially originate from a differing BGG accretion history in virialized and evolving groups. Among the halo relaxation probes, the group BGG offset appears to play a stronger role than the luminosity gap on the stellar kinematic differences of the BGGs. However, both the group BGG offset and luminosity gap appear to roughly equally drive the misalignment between the gas and stellar component of the BGGs in one direction. This study offers the first evidence that the dynamical state of galaxy groups may influence the BGG's stellar and gas kinematics, and we call for further studies using a larger sample with higher signal-to-noise.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We carry out a series of deep Karl G. Jansky Very Large Array (VLA) <jats:italic>S</jats:italic>-band observations of a sample of 21 quasars at <jats:italic>z</jats:italic> ∼ 6. The new observations expand the searches of radio continuum emission to the optically faint quasar population at the highest redshift with rest-frame <jats:inline-formula> <jats:tex-math> <?CDATA $4400\,\mathring{\rm A} $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4400</mml:mn> <mml:mspace width="0.25em" /> <mml:mi>Å</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd3a8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> luminosities down to <jats:inline-formula> <jats:tex-math> <?CDATA $3\times {10}^{11}\ {L}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>11</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em" /> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd3a8ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. We report the detections of two new radio-loud quasars: CFHQS J2242+0334 (hereafter J2242+0334) at <jats:italic>z</jats:italic> = 5.88 and CFHQS J0227−0605 (hereafter J0227−0605) at <jats:italic>z</jats:italic> = 6.20, detected with 3 GHz flux densities of <jats:inline-formula> <jats:tex-math> <?CDATA $87.0\pm 6.3\ \mu \mathrm{Jy}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>87.0</mml:mn> <mml:mo>±</mml:mo> <mml:mn>6.3</mml:mn> <mml:mspace width="0.33em" /> <mml:mi>μ</mml:mi> <mml:mi>Jy</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd3a8ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA $55.4\pm 6.7\ \mu \mathrm{Jy}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>55.4</mml:mn> <mml:mo>±</mml:mo> <mml:mn>6.7</mml:mn> <mml:mspace width="0.33em" /> <mml:mi>μ</mml:mi> <mml:mi>Jy</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd3a8ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>, respectively. Their radio loudnesses are estimated to be 54.9 ± 4.7 and 16.5 ± 3.2, respectively. To better constrain the radio-loud fraction (RLF), we combine the new measurements with the archival VLA <jats:italic>L</jats:italic>-band data as well as available data from the literature, considering the upper limits for non-detections and possible selection effects. The final derived RLF is 9.4 ± 5.7% for the optically selected quasars at <jats:italic>z</jats:italic> ∼ 6. We also compare the RLF to that of the quasar samples at low redshift and check the RLF in different quasar luminosity bins. The RLF for the optically faint objects is still poorly constrained due to the limited sample size. Our results show no evidence of significant quasar RLF evolution with redshift. There is also no clear trend of RLF evolution with quasar UV/optical luminosity due to the limited sample size of optically faint objects with deep radio observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present continued radio and X-ray observations of the previously relativistic tidal disruption event (TDE) Swift J164449.3+573451 (Sw 1644+57) extending to about 9.4 yr post disruption, as part of ongoing campaigns with the Jansky Very Large Array (VLA) and the Chandra X-ray observatory. We find that the X-ray emission has faded below detectable levels, with an upper limit of ≲3.5 × 10<jats:sup>−15</jats:sup> erg cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> in a 100 ks observation, while the radio emission continues to be detected and steadily fade. Both are consistent with forward shock emission from a non-relativistic outflow, although we find that the radio spectral energy distribution is better fit at these late times with an electron power-law index of <jats:italic>p</jats:italic> ≈ 3 (as opposed to <jats:italic>p</jats:italic> ≈ 2.5 at earlier times). With the revised spectral index we find <jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub> ≈ 0.01 using the radio and X-ray data, and a density of ≈0.04 cm<jats:sup>3</jats:sup> at a radius of <jats:italic>R</jats:italic> ≈ 0.65 pc (<jats:italic>R</jats:italic> <jats:sub>sch</jats:sub> ≈ 2 × 10<jats:sup>6</jats:sup> <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>) from the black hole. The energy scale of the blastwave is ≈10<jats:sup>52</jats:sup> erg. We also report detections of Sw 1644+57 at 3 GHz from the first two epochs of the VLA Sky Survey (VLASS), and find that ∼10<jats:sup>2</jats:sup> off-axis Sw 1644+57-like events to <jats:italic>z</jats:italic> ∼ 0.5 may be present in the VLASS data. Finally, we find that Sw 1644+57 itself will remain detectable for decades at radio frequencies, although observations at sub-GHz frequencies will become increasingly important to characterize its dynamical evolution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the present paper, we describe a theoretical model of the generation of harmonic emissions of type III solar radio bursts. The goal of our study is to fully take into account the most efficient physical processes involved in the generation of harmonic electromagnetic emission via nonlinear coupling of Langmuir waves in randomly inhomogeneous plasma of solar wind (<jats:inline-formula> <jats:tex-math> <?CDATA $l+{l}^{{\prime} }\to t$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd2bdieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). We revisit the conventional mechanism of coalescence of primarily generated and back-scattered Langmuir waves in quasihomogeneous plasma. Additionally, we propose and investigate another mechanism that generates harmonic emission only in a strongly inhomogeneous plasma: the nonlinear coupling of incident and reflected Langmuir waves inside localized regions with enhanced plasma density (clumps), in the close vicinity of the reflection point. Both mechanisms imply the presence of strong density fluctuations in plasma. We use the results of a probabilistic model of beam–plasma interaction and evaluate the efficiency of energy transfer from Langmuir waves to harmonic emission. We infer that harmonic emissions from a quasihomogeneous plasma are significantly more intense than found in previous studies. The efficiency of Langmuir wave conversion into electromagnetic harmonic emission is expected to be higher at large heliospheric distances for the mechanism operating in quasihomogeneous plasma and at small heliocentric distances for the one operating in inhomogeneous plasma. The evaluation of emission intensity in quasihomogeneous plasma may also be applied for type II solar radio bursts. The radiation pattern in both cases is quadrupolar, and we show that emission from density clumps may efficiently contribute to the visibility of harmonic radio emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hydrogen column densities inferred from X-ray absorption are typically 5–30 times larger than the neutral atomic hydrogen column densities derived from <jats:italic>λ</jats:italic>21 cm H <jats:sc>I</jats:sc> absorption toward radio-loud active galactic nuclei (AGN). Some part of the difference is ascribed to uncertainty in the spin temperature <jats:italic>T</jats:italic> <jats:sub>sp</jats:sub> = 100 K that is often used to convert <jats:italic>λ</jats:italic>21 cm H <jats:sc>I</jats:sc> absorption to <jats:italic>N</jats:italic>(H <jats:sc>I</jats:sc>). Here we propose another way to infer the gas column from H <jats:sc>I</jats:sc> absorption. In our Galaxy there is a nearly linear correlation between the inteferometrically measured integrated <jats:italic>λ</jats:italic>21 cm absorption ϒ<jats:sub>H I</jats:sub> and reddening, ϒ<jats:sub>H I</jats:sub> ∝ <jats:italic>E</jats:italic>(<jats:italic>B</jats:italic>–<jats:italic>V</jats:italic>)<jats:sup>1.10</jats:sup> for ϒ<jats:sub>H I</jats:sub> ≳ 0.7 km s<jats:sup>−1</jats:sup> or <jats:italic>E</jats:italic>(<jats:italic>B</jats:italic>–<jats:italic>V</jats:italic>) ≳ 0.04 mag. Scaling <jats:italic>E</jats:italic>(<jats:italic>B</jats:italic>–<jats:italic>V</jats:italic>) then provides the total gas column density <jats:italic>N</jats:italic>(H) from the same dust column that is responsible for optical obscuration and X-ray absorption, without calculating <jats:italic>N</jats:italic>(H <jats:sc>I</jats:sc>). Values of <jats:italic>N</jats:italic>(H) so derived typically exceed <jats:italic>N</jats:italic>(H <jats:sc>I</jats:sc>) by a factor 4 because the ubiquitous Galactic <jats:italic>λ</jats:italic>21 cm H <jats:sc>I</jats:sc> absorption samples only a portion of the interstellar gas. If the well-studied case of Hydra-A is a guide, even very large disparities in X-ray and <jats:italic>λ</jats:italic>21 cm gas column densities can be explained by resolving the core radio continuum and inferring <jats:italic>N</jats:italic>(H) from <jats:italic>λ</jats:italic>21 cm absorption. Milky Way conditions are often invoked in discussion of obscured AGN, so the empirical relationship seen in the Milky Way should be a relevant benchmark.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Extreme ultraviolet emission line profiles often show asymmetries, in the form of wing enhancements, during solar flares. Various explanations, ranging from magnetic disturbances to non-Maxwellian electron distributions to plasma turbulence have been proposed to explain these features. Plasma dynamics in a single loop can also satisfactorily explain line asymmetry. However, the presence of sub-resolution structures, confirmed by increasingly high-resolution observations, and observational difficulties in isolating a monolithic loop from nearby loops, necessitate detailed modeling efforts to investigate the effect of superposed dynamics on some line asymmetries. In the present work, we design multiloop models, representative of three possible loop configurations, to study how the resultant Fe <jats:sc>xxiii</jats:sc> spectral line profiles differ in each case and examine the differences between these multiloop models and the single loop model. We also briefly explore the role of a constant time delay in heating successive sub-loops on the spectral line shape. We find that for a multiloop model with sub-loops of the same length, heating time delay is an important factor that alters the line profile shape from the single loop case. Whereas, multiloop models with sub-loops of varied lengths predict significantly different line profiles, such as asymmetric lines for longer durations and with large blueshifts, without the necessity of introducing time delays.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the detection of the host galaxy of a damped Ly<jats:italic>α</jats:italic> system (DLA) with log <jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) [cm<jats:sup>−2</jats:sup>] = 21.0 ± 0.10 at <jats:italic>z</jats:italic> ≈ 3.0091 toward the background quasar SDSS J011852+040644 using the Palomar Cosmic Web Imager at the Hale (P200) telescope. We detect Ly<jats:italic>α</jats:italic> emission in the dark core of the DLA trough at a 3.3<jats:italic>σ</jats:italic> confidence level, with Ly<jats:italic>α</jats:italic> luminosity of <jats:italic>L</jats:italic> <jats:sub>Ly<jats:italic>α</jats:italic> </jats:sub> = (3.8 ± 0.8) × 10<jats:sup>42</jats:sup> erg s<jats:sup>−1</jats:sup>, corresponding to a star formation rate of ≳2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> (considering a lower limit on Ly<jats:italic>α</jats:italic> escape fraction <jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }\sim 2 \% $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>Ly</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>∼</mml:mo> <mml:mn>2</mml:mn> <mml:mo>%</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd1d5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) as typical for Lyman break galaxies at these redshifts. The Ly<jats:italic>α</jats:italic> emission is blueshifted with respect to the systemic redshift derived from metal absorption lines by 281 ± 43 km s<jats:sup>−1</jats:sup>. The associated galaxy is at very small impact parameter of ≲12 kpc from the background quasar, which is in line with the observed anticorrelation between column density and impact parameter in spectroscopic searches tracing the large-scale environments of DLA host galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ice dust grains composed of water, methanol, and ethanol are successfully produced in a laboratory plasma experiment operating at astrophysically relevant temperatures. Both methanol- and ethanol-ice grains grow in an elongated and branched way similar to water-ice grains formed in a plasma. The experiment reveals that methanol- and ethanol-ice grains grow faster, larger, and more branched (spikier) than water-ice grains. The observed growth features seem to be related to the fact that more source molecules and monomer grains can exist in the system at the same temperature. The observed morphology is in agreement with the characteristics of the diffusion-limited aggregation. We also find that larger and more branched ice grains form when the ambient gas pressure is low or the mass of the ambient gas is light, indicating that the aggregation of small grains is enhanced under these conditions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We applied the revised M subdwarf classification criteria discussed in Zhang et al. to Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR7 and combined the result with the M subdwarf sample from Savcheva et al. to construct a new M subdwarf sample for further study. The atmospheric parameters for each object were derived from fitting to the PHOENIX grid, and the sources with available astrometry and photometry from Gaia DR2 were combined for further analysis. The relationship between the gravity and metallicity was explored according to the locus both in the color–absolute magnitude diagram and the reduced proper motion diagram. Objects that have both the largest gravity and the lowest metallicity are located away from the main-sequence cloud and may be considered as the intrinsic M subdwarfs, which can be classified as luminosity class VI. Another group of objects whose spectra show typical M subdwarf characteristics have lower gravity and relatively moderate metal deficiency and occupy part of the ordinary M dwarf region in both diagrams. The Galactic <jats:italic>U</jats:italic>, <jats:italic>V</jats:italic>, <jats:italic>W</jats:italic> space velocity components and their dispersion show that the local Galactic halo population sampled in the solar neighborhood is represented by objects of high gravity and an inconspicuous bimodal metallicity distribution, with a fraction of prograde orbits. The other M subdwarfs seem to belong in part to the thick disk component, with a significant fraction of thin disk, moderately metal-poor objects intricately mixed with them. However, selection effects, especially the favored anticenter direction of investigation in the LAMOST subsample, as well as contamination by multiplicity and parameter coupling, could play important roles and need to be investigated further.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Active region (AR) 12673 has produced many M-class and several X-class flares, one of which being an X9.3 flare, which is recorded as the largest solar flare in solar cycle 24. We studied the evolution of the three-dimensional flare-productive magnetic field within AR 12673, using a time series of nonlinear force-free field extrapolations of every 12 hr from 2017 September 4 00:00 UT to 6 00:00 UT. Our analysis found that three magnetic flux ropes (MFRs) formed by September 4, one of which produced the X9.3 flare on September 6. One MFR has positive magnetic twist, which is a different sign from the other two MFRs. Since the temporal evolution of the magnetic flux of the MFR accumulating the positive twist is consistent with the profile of the GOES X-ray flux well observed from September 4 to 6, we suggest that the formation of the MFR having the positive twist is closely related to the occurrence of the M-class flares, including an M5.5 flare. We further found a magnetic null in the magnetic field surrounding the MFRs, in particular above the MFR having positive twist before the M5.5 flare, which is the largest M-flare observed during this period. By comparing with Atmospheric Imaging Assembly 1600 Å images, we found that the footpoints of the overlying field lines are anchored to the area where the brightening was initially observed. Therefore, we suggest that reconnection induced by the torus instability of the positively twisted MFR at the null possibly drove the M5.5 flare.</jats:p>