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<jats:title>Abstract</jats:title> <jats:p>The formation of the stellar mass within galaxy cluster cores is a poorly understood process. It features the complicated physics of cooling flows, active galactic nucleus feedback, star formation, and more. Here we study the growth of the stellar mass in the vicinity of the brightest cluster galaxy (BCG) in a <jats:italic>z</jats:italic> = 1.7 cluster, SpARCS1049+56. We synthesize a reanalysis of existing Hubble Space Telescope imaging, a previously published measurement of the star formation rate, and the results of new radio molecular gas spectroscopy. These analyses represent the past, present, and future star formation, respectively, within this system. We show that a large amount of stellar mass—between (2.2 ± 0.5) × 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and (6.6 ± 1.2) × 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> depending on the data processing—exists in a long and clumpy tail-like structure that lies roughly 12 kpc off the BCG. Spatially coincident with this stellar mass is a similarly massive reservoir ((1.0 ± 0.7) × 10<jats:sup>11</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>) of molecular gas that we suggest is the fuel for the immense star formation rate of 860 ± 130 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>, as measured by infrared observations. Hlavacek-Larrondo et al. surmised that massive, runaway cooling of the hot intracluster X-ray gas was feeding this star formation, a process that had not been observed before at high redshift. We conclude, based on the amount of fuel and current stars, that this event may be rare in the lifetime of a cluster, producing roughly 15%–21% of the intracluster light mass in one go, though perhaps a common event for all galaxy clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There exists much uncertainty surrounding interstellar grain-surface chemistry. One of the major reaction mechanisms is grain-surface diffusion for which the binding energy parameter for each species needs to be known. However, these values vary significantly across the literature which can lead to debate as to whether or not a particular reaction takes place via diffusion. In this work we employ Bayesian inference to use available ice abundances to estimate the reaction rates of the reactions in a chemical network that produces glycine. Using this we estimate the binding energy of a variety of important species in the network, by assuming that the reactions take place via diffusion. We use our understanding of the diffusion mechanism to reduce the dimensionality of the inference problem from 49 to 14, by demonstrating that reactions can be separated into classes. This dimensionality reduction makes the problem computationally feasible. A neural network statistical emulator is used to also help accelerate the Bayesian inference process substantially. The binding energies of most of the diffusive species of interest are found to match some of the disparate literature values, with the exceptions of atomic and diatomic hydrogen. The discrepancies between these two species are related to the limitations of the physical and chemical models. However, the use of a dummy reaction of the form H + X <jats:inline-formula> <jats:tex-math> <?CDATA $\longrightarrow $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>⟶</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6606ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> HX is found to somewhat reduce the discrepancy with the binding energy of atomic hydrogen. Using the inferred binding energies in the full gas–grain version of UCLCHEM results in almost all the molecular abundances being recovered.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent gravitational-wave observations showed that binary black hole (BBH) mergers with massive components are more likely to have high effective spins. In the model of isolated binary evolution, BH spins mainly originate from the angular momenta of the collapsing cores before BH formation. Both observations and theories indicate that BHs tend to possess relatively low spins; the origin of fast-spinning BHs remains a puzzle. We investigate an alternative process that stable Case A mass transfer may significantly increase BH spins during the evolution of massive BH binaries. We present detailed binary evolution calculations and find that this process can explain the observed high spins of some massive BBH mergers under the assumption of mildly super-Eddington accretion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A bright hard X-ray coronal source observed at the early stage of solar flares is considered. The plasma density in a quiet corona is not enough to explain the hard X-ray bremsstrahlung radiation. The generally accepted concept of increasing plasma density in the looptop is associated with the effect of evaporation of hot chromosphere plasma. We discuss the increase in plasma density at the looptop at the early stage of a flare, due to magnetic loop contraction during the relaxation of the magnetic field (the so-called collapsing trap model). In this case, the increase in the plasma density at the looptop occurs on a timescale of seconds–tens of seconds, while the process of plasma evaporation increases the plasma density for much longer. The Fokker–Planck kinetic equation for accelerated electrons with a betatron and Fermi terms is solved numerically. We calculate increases in the energy of the accelerated electrons, the energy spectrum, and the pitch-angle anisotropy due to betatron and Fermi first-order acceleration. For a collapse time of 8 s, the total energy of the accelerated electrons increases by ∼20%–200%, depending on the model parameters. The ratio of the looptop/total hard X-ray flux at 29–58 keV increases by 15%–30% in the collapsing trap model. It is shown that this model can explain the appearance of bright coronal hard X-ray sources in the first seconds–tens of seconds after the hard X-ray flux starts growing.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present high spatial resolution (∼0.″4, 2.2 kpc) observations of the CO(6−5), CO(7−6), and [C <jats:sc>i</jats:sc>]<jats:sub>369 <jats:italic>μ</jats:italic>m</jats:sub> lines and dust continuum emission from the interstellar medium (ISM) in the host galaxy of the quasar J0305−3150 at <jats:italic>z</jats:italic> = 6.6. These, together with archival [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> data at a comparable spatial resolution, enable studies of the spatial distribution and kinematics between the ISM in different phases. When comparing the radial profiles of CO, [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>, and the dust continuum, we find that the CO and dust continuum exhibit similar spatial distributions, both of which are less extended than the [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>, indicating that the CO and dust continuum are tracing the same gas component, while the [C <jats:sc>ii</jats:sc>]158 <jats:italic>μ</jats:italic>m is tracing a more extended one. In addition, we derive the radial profiles of the [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>/CO, [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>/far-infrared (FIR), CO/FIR, and dust continuum <jats:italic>S</jats:italic> <jats:sub>98.7 GHz</jats:sub>/<jats:italic>S</jats:italic> <jats:sub>258.1 GHz</jats:sub> ratios. We find a decreasing <jats:italic>S</jats:italic> <jats:sub>98.7 GHz</jats:sub>/<jats:italic>S</jats:italic> <jats:sub>258.1 GHz</jats:sub> ratio with radius, possibly indicating a decrease of dust optical depth with increasing radius. We also detect some of the ISM lines and continuum emission in the companion galaxies previously discovered in the field around J0305−3150. Through comparing the line-to-line and line-to-FIR ratios, we find no significant differences between the quasar and its companion galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the CO(1–0)-to-H<jats:sub>2</jats:sub> conversion factor (<jats:italic>X</jats:italic> <jats:sub>CO</jats:sub>) and the line ratio of CO(2–1)-to-CO(1–0) (<jats:italic>R</jats:italic> <jats:sub>21</jats:sub>) across a wide range of metallicity (0.1 ≤ <jats:italic>Z</jats:italic>/<jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub> ≤ 3) in high-resolution (∼0.2 pc) hydrodynamical simulations of a self-regulated multiphase interstellar medium. We construct synthetic CO emission maps via radiative transfer and systematically vary the <jats:italic>observational </jats:italic>beam size to quantify the scale dependence. We find that the kpc-scale <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> can be overestimated at low <jats:italic>Z</jats:italic> if assuming steady-state chemistry or assuming that the star-forming gas is H<jats:sub>2</jats:sub> dominated. On parsec scales, <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> varies by orders of magnitude from place to place, primarily driven by the transition from atomic carbon to CO. The parsec-scale <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> drops to the Milky Way value of <jats:inline-formula> <jats:tex-math> <?CDATA $2\times {10}^{20}\ {\mathrm{cm}}^{-2}\,{\left({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\right)}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>20</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em" /> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> <mml:mspace width="0.25em" /> <mml:mi>km</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac65fdieqn1.gif" xlink:type="simple" /> </jats:inline-formula> once dust shielding becomes effective, independent of <jats:italic>Z</jats:italic>. The CO lines become increasingly optically thin at lower <jats:italic>Z</jats:italic>, leading to a higher <jats:italic>R</jats:italic> <jats:sub>21</jats:sub>. Most cloud area is filled by diffuse gas with high <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> and low <jats:italic>R</jats:italic> <jats:sub>21</jats:sub>, while most CO emission originates from dense gas with low <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> and high <jats:italic>R</jats:italic> <jats:sub>21</jats:sub>. Adopting a constant <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> strongly over- (under-)estimates H<jats:sub>2</jats:sub> in dense (diffuse) gas. The line intensity negatively (positively) correlates with <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> (<jats:italic>R</jats:italic> <jats:sub>21</jats:sub>) as it is a proxy of column density (volume density). On large scales, <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> and <jats:italic>R</jats:italic> <jats:sub>21</jats:sub> are dictated by beam averaging, and they are naturally biased toward values in dense gas. Our predicted <jats:italic>X</jats:italic> <jats:sub>CO</jats:sub> is a multivariate function of <jats:italic>Z</jats:italic>, line intensity, and beam size, which can be used to more accurately infer the H<jats:sub>2</jats:sub> mass.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Diffusive shock acceleration at collisionless shocks remains the most likely process for accelerating particles in a variety of astrophysical sources. While the standard prediction for strong shocks is that the spectrum of accelerated particles is universal, <jats:italic>f</jats:italic>(<jats:italic>p</jats:italic>) ∝ <jats:italic>p</jats:italic> <jats:sup>−4</jats:sup>, numerous phenomena affect this simple conclusion. In general, the nonlinear dynamical reaction of accelerated particles leads to a concave spectrum, steeper than <jats:italic>p</jats:italic> <jats:sup>−4</jats:sup> at momenta below a few tens of GeV <jats:italic>c</jats:italic> <jats:sup>−1</jats:sup> and harder than the standard prediction at high energies. However, the nonlinear effects become important in the presence of magnetic field amplification, which in turn leads to higher values of the maximum momentum <jats:italic>p</jats:italic> <jats:sub>max</jats:sub>. It was recently discovered that the self-generated perturbations that enhance particle scattering, when advected downstream, move in the same direction as the background plasma, so that the effective compression factor at the shock decreases and the spectrum becomes steeper. We investigate the implications of the excitation of the non-resonant streaming instability on these spectral deformations, the dependence of the spectral steepening on the shock velocity, and the role played by the injection momentum.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Measuring the density of the intergalactic medium using quasar sight lines in the epoch of reionization is challenging due to the saturation of Ly<jats:italic>α</jats:italic> absorption. Near a luminous quasar, however, the enhanced radiation creates a proximity zone observable in the quasar spectra where the Ly<jats:italic>α</jats:italic> absorption is not saturated. In this study, we use 10 high-resolution (<jats:italic>R</jats:italic> ≳ 10,000) <jats:italic>z</jats:italic> ∼ 6 quasar spectra from the extended XQR-30 sample to measure the density field in the quasar proximity zones. We find a variety of environments within 3 pMpc distance from the quasars. We compare the observed density cumulative distribution function (CDF) with models from the Cosmic Reionization on Computers simulation and find a good agreement between 1.5 and 3 pMpc from the quasar. This region is far away from the quasar hosts and hence approaching the mean density of the universe, which allows us to use the CDF to set constraints on the cosmological parameter <jats:italic>σ</jats:italic> <jats:sub>8</jats:sub> = 0.6 ± 0.3. The uncertainty is mainly due to the limited number of high-quality quasar sight lines currently available. Utilizing the more than 200 known quasars at <jats:italic>z</jats:italic> ≳ 6, this method will allow us to tighten the constraint on <jats:italic>σ</jats:italic> <jats:sub>8</jats:sub> to the percent level in the future. In the region closer to the quasar within 1.5 pMpc, we find that the density is higher than predicted in the simulation by 1.23 ± 0.17, suggesting that the typical host dark matter halo mass of a bright quasar (<jats:italic>M</jats:italic> <jats:sub>1450</jats:sub> &lt; −26.5) at <jats:italic>z</jats:italic> ∼ 6 is <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}({M}_{h}/{M}_{\odot })={12.5}_{-0.7}^{+0.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>12.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac658dieqn1.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>With the ever-increasing detection of sulfur-bearing molecules and the high abundance and refractory nature of aluminum, the [Al, S, O<jats:sub>2</jats:sub>] isomers may play an important role in the gas-phase chemistry of circumstellar envelopes and the chemistry on the surface of dust grains. High-level theoretical exploration of the [Al, S, O<jats:sub>2</jats:sub>] molecular system yielded five isomers, and predictions of their rotational, vibrational, and electronic spectroscopic properties are provided to inform experimental and observational searches. Cis-AlOSO and diamond isomers are isoenergetic and connected via a very small (∼1 kcal mol<jats:sup>−1</jats:sup>) transition-state barrier. These isomers may act as intermediates along the chemical pathway between Al + SO<jats:sub>2</jats:sub> and AlO + SO. Other isomers OAlOS and SAlO<jats:sub>2</jats:sub> are stable relative to their corresponding dissociation asymptotes. Large permanent dipole moments of 2.521 D (cis-AlOSO), 1.239 D (diamond), and 5.401 D (OAlOS) predict strong rotational transitions and indicate these molecules as prime candidates for experimental study. Due to the low transition-state barrier, mixing of the vibrational levels is anticipated, complicating the vibrational spectrum. Electronic spectroscopy may be used as a means to differentiate between the two isomers. Strong electronic transitions are predicted to occur in the 200–300 nm range for cis-AlOSO and diamond. Simulated electronic absorption spectra provide a starting point for experimental characterization and spectral deconvolution of these isomers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ion escape from the atmosphere to space is one of the most likely reasons to account for the evolution of the Martian climate. Based on three-dimensional multifluid magnetohydrodynamic simulations, we investigated the impact of the magnetic inclination angle on O<jats:sup>+</jats:sup> escape at low altitudes of 275–1000 km under the typical solar wind conditions. Numerical results showed that an outward ion velocity in the direction opposite to the electromagnetic (EM) force results in weak outward flux and leads to ions becoming trapped by the horizontal magnetic field lines at the local horizontal magnetic equator. Much of the EM force can be attributed to the Hall electric force. In the region of high absolute magnetic inclination angle, the outward ion velocity has the same direction as the EM force, which increases the outward flux and causes ions to diffuse upward along open magnetic field lines to higher altitude. In addition, the EM force is mainly provided by the electron pressure gradient force and the motional electric force. Global results for the magnetic inclination angle indicate that the strong crustal field regions in the southern hemisphere are mainly occupied by magnetic field lines with high absolute magnetic inclination angle, while horizontal field lines are dominant in the northern hemisphere, which leads to a higher O<jats:sup>+</jats:sup> escape rate in the Martian southern hemisphere than in the northern, from altitudes of 275 to 1000 km. This is a significant advance in understanding the impact and mechanism of the Martian magnetic field directions on ion escape.</jats:p>