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<jats:title>Abstract</jats:title> <jats:p>Environmental effects are crucial to the understanding of the evolution of galaxies in dense environments, such as galaxy clusters. Using the large field of view of SITELLE, the unique imaging Fourier transform spectrograph at the Canada–France–Hawaii Telescope, we are able to obtain 2D spectral information for a large and complete sample of cluster galaxies out to the infall region. We describe a pipeline developed to identify emission-line galaxies (ELGs) from the datacube using cross-correlation techniques. We present results based on the spatial offsets between the emission-line regions and stellar continua in ELGs from two <jats:italic>z</jats:italic> ∼ 0.25 galaxy clusters, Abell 2390 and A2465. We find a preference for the offsets to be pointed away from the cluster center. Combining the two clusters, there is a 3<jats:italic>σ</jats:italic> excess for high-velocity galaxies within the virial radius to have the offsets pointed away from the cluster center. Assuming the offset is a proxy for the velocity vector of a galaxy, as expected from ram pressure stripping, this excess indicates that ram pressure stripping occurs most effectively during the first passage of an infalling galaxy, leading to the quenching of its star formation. We also find that, outside the virial region, the continuum-normalized H<jats:italic>α</jats:italic> line flux for infalling galaxies with large offsets is on average lower than those with small or no measurable offset, further supporting ram pressure as a dominant quenching mechanism during the initial infall stages.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use photometry and proper motions from Gaia DR2 to determine the blue straggler star (BSS) populations of 16 old (1–10 Gyr), nearby (<jats:italic>d</jats:italic> &lt; 3500 pc) open clusters. We find that the fractional number of BSS compared to red giant branch stars increases with age, starting near zero at 1 Gyr and flattening to ∼0.35 by 4 Gyr. Fitting stellar evolutionary tracks to these BSSs, we find that their mass distribution peaks at a few tenths of a solar mass above the main-sequence turnoff. BSSs more than 0.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> above the turnoff make up only ∼25% of the sample, and BSSs more than 1.0 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> above the turnoff are rare. We compare this to Compact Object Synthesis and Monte Carlo Investigation Code<jats:monospace /> population synthesis models of BSSs formed via mass transfer. We find that standard population synthesis assumptions dramatically under-produce the number of BSS in old open clusters. We also find that these models overproduce high-mass BSSs relative to lower-mass BSSs. The expected number of BSSs formed through dynamics do not fully account for this discrepancy. We conclude that in order to explain the observed BSS populations from Roche lobe overflow, mass transfer from giant donors must be more stable than assumed in canonical mass-transfer prescriptions, and including nonconservative mass transfer is important in producing realistic BSS masses. Even with these modifications, it is difficult to achieve the large number of BSSs observed in the oldest open clusters. We discuss some additional physics that may explain the large number of observed blue stragglers among old stellar populations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigenmode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the ohmic resistivity and the other being the resonant absorption of SSKMs in the cusp and Alfvén continua. We find that the relative importance of the two mechanisms depends sensitively on the magnetic Reynolds number (<jats:italic>R</jats:italic> <jats:sub>m</jats:sub>). Resonant absorption is the sole damping mechanism for realistically large values of <jats:italic>R</jats:italic> <jats:sub>m</jats:sub>, and the cusp resonance in general dominates the Alfvén one unless the axial wavenumbers are at the lower end of the observationally relevant range. We also find that the thin-boundary approximation holds only when the TL-width-to-radius ratios are much smaller than nominally expected. The ohmic resistivity is far more important for realistically small <jats:italic>R</jats:italic> <jats:sub>m</jats:sub>. Even in this case, SSKMs are only marginally damped, with damping-time-to-period ratios reaching ∼10 in the parameter range we examine.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use Atacama Large Millimeter/submillimeter Array CO (2–1) observations of six low-redshift Palomar-Green quasars to study the distribution and kinematics of the molecular gas of their host galaxies at kiloparsec-scale resolution. While the molecular gas content, molecular gas fraction, and star formation rates are similar to those of nearby massive, star-forming galaxies, the quasar host galaxies possess exceptionally compact, disky molecular gas distributions with a median half-light radius of 1.8 kpc and molecular gas mass surface densities ≳22 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> pc<jats:sup>−2</jats:sup>. While the overall velocity field of the molecular gas is dominated by regular rotation out to large radii, with ratio of rotation velocity to velocity dispersion ≳9, the nuclear region displays substantial kinematic complexity associated with small-scale substructure in the gas distribution. A tilted-ring analysis reveals that the kinematic and photometric position angles are misaligned on average by ∼ 34° ± 26° and provides evidence of kinematic twisting. These observations provide tantalizing clues to the detailed physical conditions of the circumnuclear environments of actively accreting supermassive black holes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present near-IR (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2020oi in the galaxy M100 and the broad-lined SN Ic SN 2020bvc in UGC 9379, using Gemini, Las Cumbres Observatory, Southern Astrophysical Telescope, and other ground-based telescopes. The NIR spectrum of SN 2020oi at day 63 since the explosion shows strong CO emissions and a rising <jats:italic>K</jats:italic>-band continuum, which is the first unambiguous dust detection from an SN Ic. Non-LTE CO modeling shows that CO is still optically thick and that the lower limit to the CO mass is 10<jats:sup>−3</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The dust temperature is 810 K, and the dust mass is ∼10<jats:sup>−5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We explore the possibilities that the dust is freshly formed in the ejecta, heated dust in the preexisting circumstellar medium, and an infrared echo. The light curves of SN 2020oi are consistent with a STELLA model with canonical explosion energy, 0.07 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> Ni mass, and 0.7 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ejecta mass. A model of high explosion energy of 10<jats:sup>52</jats:sup> erg, 0.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> Ni mass, and 6.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ejecta mass with the circumstellar matter reproduces the double-peaked light curves of SN 2020bvc. We observe temporal changes of absorption features of the IR Ca <jats:sc>ii</jats:sc> triplet, S <jats:sc>i</jats:sc> at 1.043 <jats:italic>μ</jats:italic>m, and Fe <jats:sc>ii</jats:sc> at 5169 Å. The blueshifted lines indicate high velocities, up to 60,000 km s<jats:sup>−1</jats:sup> for SN 2020bvc and 20,000 km s<jats:sup>−1</jats:sup> for SN 2020oi, and the expansion velocity rapidly declines before the optical maximum. We present modeled spectral signatures and diagnostics of CO and SiO molecular bands between 1.4 and 10 <jats:italic>μ</jats:italic>m.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the quest to solve the long-standing coronal heating problem, it was suggested half a century ago that coronal loops could be heated by waves. Despite the accumulating observational evidence of the possible importance of coronal waves, still no 3D MHD simulations exist that show significant heating by MHD waves. Here we report on the first 3D coronal loop model that heats the plasma against radiative cooling. The coronal loop is driven at the footpoint by transverse oscillations, and subsequently the induced Kelvin–Helmholtz instability deforms the loop cross section and generates small-scale structures. Wave energy is transferred to smaller scales where it is dissipated, overcoming the internal energy losses by radiation. These results open up a new avenue to address the coronal heating problem.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The H<jats:sub>2</jats:sub> molecule has two nuclear spin isomers, the so-called ortho and para isomers. Nuclear spin conversion (NSC) between these states is forbidden in the gas phase. The energy difference between the lowest ortho and para states is as large as 14.7 meV, corresponding to ∼170 K. Therefore, each state of H<jats:sub>2</jats:sub> differently affects not only the chemistry but also the macroscopic gas dynamics in space; thus, the ortho-to-para abundance ratio (OPR) of H<jats:sub>2</jats:sub> has significant impacts on various astronomical phenomena. For a long time, the OPR of nascent H<jats:sub>2</jats:sub> upon formation on dust grains has been assumed to have a statistical value of 3 and to gradually equilibrate in the gas phase at the temperature of the circumstances. Recently, the NSC of H<jats:sub>2</jats:sub> was experimentally revealed to occur on water ice at very low temperatures and thus incorporated into gas–dust chemical models. However, H<jats:sub>2</jats:sub> molecules should form well before dust grains are coated by water ice. Information about how the OPR of H<jats:sub>2</jats:sub> behaves on bare silicate dust before ice-mantle formation is lacking. Knowing the influence of the OPR of H<jats:sub>2</jats:sub> is desirable, if the OPR changes even on a bare silicate surface within an astronomically meaningful timescale. We report the first laboratory measurements of the NSC of H<jats:sub>2</jats:sub> physisorbed on amorphous silicate (Mg<jats:sub>2</jats:sub>SiO<jats:sub>4</jats:sub>) at temperatures up to 18 K. The conversion was found to occur very rapidly.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Atacama Large Millimeter/submillimeter Array [C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m line and far-infrared (FIR) continuum emission observations toward HSC J120505.09−000027.9 (J1205−0000) at <jats:italic>z</jats:italic> = 6.72 with a beam size of ∼0.″8 × 0.″5 (or 4.1 kpc × 2.6 kpc), the most distant red quasar known to date. Red quasars are modestly reddened by dust and are thought to be in rapid transition from an obscured starburst to an unobscured normal quasar, driven by powerful active galactic nucleus (AGN) feedback that blows out a cocoon of interstellar medium. The FIR continuum of J1205−0000 is bright, with an estimated luminosity of <jats:italic>L</jats:italic> <jats:sub>FIR</jats:sub> ∼ 3 × 10<jats:sup>12</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>. The [C <jats:sc>ii</jats:sc>] line emission is extended on scales of <jats:italic>r</jats:italic> ∼ 5 kpc, greater than that of the FIR continuum. The line profiles at the extended regions are complex and broad (FWHM ∼ 630–780 km s<jats:sup>−1</jats:sup>). Although it is not practical to identify the nature of this extended structure, possible explanations include (i) companion/merging galaxies and (ii) massive AGN-driven outflows. For the case of (i), the companions are modestly star-forming (∼10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>) but are not detected by our Subaru optical observations (<jats:italic>y</jats:italic> <jats:sub>AB,5<jats:italic>σ</jats:italic> </jats:sub> = 24.4 mag). For the case of (ii), our lower limit to the cold neutral outflow rate is ∼100 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. The outflow kinetic energy and momentum are both much lower than predicted in energy-conserving wind models, suggesting that the AGN feedback in this quasar is not capable of completely suppressing its star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Forbush decreases (Fds) in galactic cosmic ray intensity are related to interplanetary coronal mass ejections (ICMEs). The parallel diffusion of particles is reduced because the magnetic turbulence level in the sheath region bounded by the ICME’s leading edge and shock is high. In the sheath and magnetic cloud (MC) energetic particles would feel an enhanced magnetic focusing effect caused by the strong inhomogeneity of the background magnetic field. Therefore, particles would be partially blocked in the sheath–MC structure. Here, we study two-step Fds by considering the magnetic turbulence and background magnetic field in the sheath–MC structure with diffusion coefficients calculated using theoretical models, to reproduce the Fd associated with the ground-level enhancement event on 2000 July 14 by solving the focused transport equation. The sheath and MC are set to spherical caps that are portions of spherical shells with enhanced background magnetic field. The magnetic turbulence levels in the sheath and MC are set to higher and lower than those in ambient solar wind, respectively. In general, the simulation result conforms to the main characteristics of the Fd observation, such as the pre-increase precursor, amplitude, total recovery time, and two-step decrease of the flux at the arrival of the sheath and MC. It is suggested that the sheath plays an important role in the amplitude of the Fd while the MC contributes to the formation of the second-step decrease and prolonged recovery time. It is also inferred that both magnetic turbulence and background magnetic field in the sheath–MC structure are important for reproducing the observed two-step Fd.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>By analyzing the magnetosheath measurements from the Magnetospheric Multiscale Spacecraft, we obtain statistical results for the contribution of magnetic reconnection (MR) events at electron scales to the energy dissipation of coherent structures in shocked turbulent plasmas. The partial variance of increments (PVI) method is employed to find coherent structures in the magnetic field data. We consider criteria to further identify MR events, such as reversal of magnetic field components, significant energy dissipation, and evident electron outflow velocity. Statistically, for most MR events, their PVI values are larger than those of other types of coherent structures, and their energy dissipations are also stronger. However, due to the relatively small number of MR events, their contribution to coherent structures’ energy dissipation is relatively trivial. If the dissipation of non-coherent structures is taken into account, MR’s contribution to energy dissipation would be even less. Hence, we suggest that MR events, though having strong dissipation locally, are not the major contributor to energy dissipation in the turbulent magnetosheath. After analyzing the features of non-MR current sheets, we propose that these are mainly coherent structures inherent to kinetic Alfvén fluctuations.</jats:p>