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<jats:title>Abstract</jats:title> <jats:p>The mirror-mode structures in the Martian magnetosheath that were observed by Mars Atmosphere and Volatile Evolution during 2015–2018 are analyzed statistically. It is found that most mirror-mode events occurred close to the bow shock. Morphological categorization based on skewness of the magnetic field shows that ∼46.57% of the observed mirror-mode events are peak-like, ∼40.25% are wave-like, and ∼13.18% are dip-like. The mirror-mode structures mostly saturate in a very short time after their formation near the bow shock, which is a result of the high temperature anisotropy and high plasma beta at this location. Carried downstream by the magnetosheath flow, the mirror-mode structures remain in nonlinear saturation states. Meanwhile, the dayside magnetosheath plasma largely deviates from marginal stability, which is a state commonly that is expected in the terrestrial magnetosheath. By flowline tracing in an MHD model, it is found the mirror structures can be divided into two groups: ∼80% of the events that are observed near the bow shock evolve less than 10 s in plasma with high temperature anisotropy and high plasma beta value, keeping in saturated states; the other 20% of the events evolve following a similar process to that at the Earth, undergoing morphology transition in response to the local plasma conditions. However, the dayside magnetosheath is largely in an unstable condition, which prevents the mirror-mode structures from fully evolving into the decaying phase. Our results suggest that energy dispassion through wave-particle interaction might not be sufficient to remove the free energy that is introduced by the solar wind–Mars interaction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use the age measurements of 114 old astrophysical objects (OAO) in the redshift range 0 ≲ <jats:italic>z</jats:italic> ≲ 8 to explore the Hubble tension. The age of the universe at any <jats:italic>z</jats:italic> is inversely proportional to the Hubble constant, <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>, so requiring the universe to be older than the OAO it contains at any <jats:italic>z</jats:italic> will lead to an upper limit on <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>. Assuming flat ΛCDM and setting a Gaussian prior on the matter density parameter Ω<jats:sub>m</jats:sub> = 0.315 ± 0.007 informed by Planck, we obtain a 95% confidence level upper limit of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> &lt; 70.6 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup>, representing a 2<jats:italic>σ</jats:italic> tension with the measurement using the local distance ladder. We find, however, that the inferred upper limit on <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> depends quite sensitively on the prior for Ω<jats:sub>m</jats:sub>, and the Hubble tension between early-time and local measurements of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> may be due in part to the inference of both Ω<jats:sub>m</jats:sub> and <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> in Planck, while the local measurement uses only <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>. The age-redshift data may also be used for cosmological model comparisons. We find that the <jats:italic>R</jats:italic> <jats:sub>h</jats:sub> = <jats:italic>ct</jats:italic> universe accounts well for the data, with a reasonable upper limit on <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>, while Einstein–de Sitter fails to pass the cosmic-age test. Finally, we present a model-independent estimate of the spatial curvature using the ages of 61 galaxies and the luminosity distances of 1048 Pantheon Type Ia supernovae. This analysis suggests that the geometry of the universe is marginally consistent with spatial flatness at a confidence level of 1.6<jats:italic>σ</jats:italic>, characterized as <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{k}={0.43}_{-0.27}^{+0.27}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>k</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.43</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.27</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.27</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac562cieqn1.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observing in six frequency bands from 27 to 280 GHz over a large sky area, the Simons Observatory (SO) is poised to address many questions in Galactic astrophysics in addition to its principal cosmological goals. In this work, we provide quantitative forecasts on astrophysical parameters of interest for a range of Galactic science cases. We find that SO can: constrain the frequency spectrum of polarized dust emission at a level of Δ<jats:italic>β</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub> ≲ 0.01 and thus test models of dust composition that predict that <jats:italic>β</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub> in polarization differs from that measured in total intensity; measure the correlation coefficient between polarized dust and synchrotron emission with a factor of two greater precision than current constraints; exclude the nonexistence of exo-Oort clouds at roughly 2.9<jats:italic>σ</jats:italic> if the true fraction is similar to the detection rate of giant planets; map more than 850 molecular clouds with at least 50 independent polarization measurements at 1 pc resolution; detect or place upper limits on the polarization fractions of CO(2–1) emission and anomalous microwave emission at the 0.1% level in select regions; and measure the correlation coefficient between optical starlight polarization and microwave polarized dust emission in 1° patches for all lines of sight with <jats:italic>N</jats:italic> <jats:sub>H</jats:sub> ≳ 2 × 10<jats:sup>20</jats:sup> cm<jats:sup>−2</jats:sup>. The goals and forecasts outlined here provide a roadmap for other microwave polarization experiments to expand their scientific scope via Milky Way astrophysics.<jats:xref ref-type="fn" rid="apjac5e36fn1"> <jats:sup>37</jats:sup> </jats:xref> <jats:fn id="apjac5e36fn1"> <jats:label> <jats:sup>37</jats:sup> </jats:label> <jats:p>A supplement describing author contributions to this paper can be found at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://simonsobservatory.org/wp-content/uploads/2022/02/SO_GS_Contributions.pdf" xlink:type="simple">https://simonsobservatory.org/wp-content/uploads/2022/02/SO_GS_Contributions.pdf</jats:ext-link>.</jats:p> </jats:fn> </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Close-in giant planets with strong stellar irradiation show atmospheric circulation patterns with strong equatorial jets and global-scale stationary waves. So far, almost all modeling works on atmospheric circulations of such giant planets have mainly considered external radiation alone, without taking into account the role of internal heat fluxes or just treating it in very simplified ways. Here, we study atmospheric circulations of strongly irradiated giant planets by considering the effect of internal forcing, which is characterized by small-scale stochastic interior thermal perturbations, using a three-dimensional atmospheric general circulation model. We show that the perturbation-excited waves can largely modify atmospheric circulation patterns in the presence of relatively strong internal forcing. Specifically, our simulations demonstrate three circulation regimes: a superrotation regime, a midlatitude-jet regime, and a quasi-periodic oscillation regime, depending on the relative importance of external and internal forcings. It is also found that strong internal forcing can cause noticeable modifications of the thermal phase curves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We model here the merger histories of the supermassive black hole (SMBH) population in the late stages of a cosmological simulation of a ∼ 2 × 10<jats:sup>13</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> galaxy group. The gravitational dynamics around the several tens of SMBHs (<jats:italic>M</jats:italic> <jats:sub>•</jats:sub> &gt; 7.5 × 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) hosted by the galaxies in the group is computed at high accuracy using regularized integration with the KETJU code. The 11 SMBHs that form binaries and a hierarchical triplet eventually merge after hardening through dynamical friction, stellar scattering, and gravitational wave (GW) emission. The binaries form at eccentricities of <jats:italic>e</jats:italic> ∼ 0.3–0.9, with one system evolving to a very high eccentricity of <jats:italic>e</jats:italic> = 0.998, and merge on timescales of a few tens to several hundred megayears. During the simulation, the merger-induced GW recoil kicks eject one SMBH remnant from the central host galaxy. This temporarily drives the galaxy off the <jats:italic>M</jats:italic> <jats:sub>•</jats:sub>–<jats:italic>σ</jats:italic> <jats:sub>⋆</jats:sub> relation; however, the galaxy returns to the relation due to subsequent galaxy mergers, which bring in new SMBHs. This showcases a possible mechanism contributing to the observed scatter of the <jats:italic>M</jats:italic> <jats:sub>•</jats:sub>–<jats:italic>σ</jats:italic> <jats:sub>⋆</jats:sub> relation. Finally, we show that pulsar timing arrays and <jats:italic>LISA</jats:italic> would be able to detect parts of the GW signals from the SMBH mergers that occur during the ∼4 Gyr time span simulated with KETJU.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Over the course of the third observing run of the LIGO–Virgo–KAGRA Collaboration, several gravitational-wave (GW) neutron star–black hole (NSBH) candidates have been announced. By assuming that these candidates are real signals with astrophysical origins, we analyze the population properties of the mass and spin distributions for GW NSBH mergers. We find that the primary BH mass distribution of NSBH systems, whose shape is consistent with that inferred from the GW binary BH (BBH) primaries, can be well described as a power law with an index of <jats:inline-formula> <jats:tex-math> <?CDATA $\alpha ={4.8}_{-2.8}^{+4.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac540cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> plus a high-mass Gaussian component peaking at <jats:inline-formula> <jats:tex-math> <?CDATA $\sim {33}_{-9}^{+14}\,{M}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>33</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>M</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="apjac540cieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. The NS mass spectrum could be shaped as a nearly flat distribution between ∼1.0 and 2.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The constrained NS maximum mass agrees with that inferred from NSs in our Galaxy. If GW190814 and GW200210 are NSBH mergers, the posterior results of the NS maximum mass would be always larger than ∼2.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and significantly deviate from that inferred in Galactic NSs. The effective inspiral spin and effective precession spin of GW NSBH mergers are measured to potentially have near-zero distributions. The negligible spins for GW NSBH mergers imply that most events in the universe should be plunging events, which support the standard isolated formation channel of NSBH binaries. More NSBH mergers to be discovered in the fourth observing run would help to more precisely model the population properties of cosmological NSBH mergers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The continuous nanohertz gravitational waves (GWs) from individual supermassive binary black holes (SMBBHs) can be encoded in the timing residuals of pulsar timing arrays (PTAs). For each pulsar, the residuals actually contain an Earth term and a pulsar term, but usually only the Earth term is considered as a signal and the pulsar term is dropped. This leads to parameter-estimation biases (PEBs) for the SMBBHs, and currently there are no convenient evaluations of the PEBs. In this article, we formulate the PEBs for a SMBBH with an eccentric orbit. In our analyses, the unknown phases of pulsar terms are treated as random variables obeying the uniform distribution <jats:italic>U</jats:italic>[0, 2<jats:italic>π</jats:italic>), due to the fact that pulsar distances are generally poorly measured. Our analytical results are in accordance with the numerical work by Zhu et al. at 1.5<jats:italic>σ</jats:italic> level, which implies that our formulae are effective in estimating magnitudes of the PEBs. Additionally, we find that the biases Δ<jats:italic>φ</jats:italic> <jats:sup> <jats:italic>E</jats:italic> </jats:sup> and Δ<jats:italic>e</jats:italic>/<jats:italic>e</jats:italic> for two parameters—that is, Earth-term phase <jats:italic>φ</jats:italic> <jats:sup> <jats:italic>E</jats:italic> </jats:sup> and orbital eccentricity <jats:italic>e</jats:italic>—monotonically decrease as <jats:italic>e</jats:italic> increases, which partly confirms a hypothesis in our previous work. Furthermore, we also calculate the PEBs caused by the recently observed common-spectrum process (CSP). We find that if the strain amplitude of the continuous GW is significantly stronger (three times larger, in our cases) than the stochastic GW background, then the PEBs from pulsar terms are larger than those from the CSP. Our formulae of the PEBs can be conveniently applied in the future PTA data analyses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyzed the unexposed to the sky (outFOV) region of the MOS2 detector on board XMM-Newton covering 15 yr of data amounting to 255 Ms. We show convincing evidence that the origin of the unfocused background in XMM-Newton is due to energetic protons, electrons, and hard X-ray photons. Galactic cosmic rays are the main contributors as shown by the tight correlation (2.6% of total scatter) with the 1 GeV proton data of the SOHO EPHIN detector. Tight correlations are found with a proxy of the Chandra background rate, revealing the common source of background for detectors in similar orbits, and with the data of the EPIC Radiation Monitor, only when excluding Solar energetic particle events. The entrance to the outer electron belts is associated with a sudden increase in the outFOV MOS2 rate and a spectral change. These facts support the fact that MeV electrons can generate an unfocused background signal. The correlation between MOS2 outFOV data and the SOHO EPHIN data reveals a term constant in time and isotropic, similar to the one found in the study of the pn data. The most plausible origin of this component is hard unfocused X-ray photons of the cosmic X-ray background Compton scattering in the detector as supported by the strength of the signal in the two detectors with different thicknesses. Based on this physical understanding, a particle radiation monitor on board the Advanced Telescope for High Energy Astrophysics has been proposed and it is currently under study. It will be able to track different species with the necessary accuracy and precision to guarantee the challenging requirement of 2% reproducibility of the background.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Efforts to discover and characterize habitable zone planets have primarily focused on Sun-like stars and M dwarfs. K stars, however, provide an appealing compromise between these two alternatives that has been relatively unexplored. Understanding the ultraviolet (UV) environment around such stars is critical to our understanding of their planets, as the UV can drastically alter the photochemistry of a planet’s atmosphere. Here we present near-UV and far-UV Hubble Space Telescope's Cosmic Origins Spectrograph observations of 39 K stars at three distinct ages: 40 Myr, 650 Myr, and ≈5 Gyr. We find that the K star (0.6–0.8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) UV flux remains constant beyond 650 Myr before falling off by an order of magnitude by field age. This is distinct from early M stars (0.3–0.6 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), which begin to decline after only a few hundred megayears. However, the rotation–UV activity relation for K stars is nearly identical to that of early M stars. These results may be a consequence of the spin-down stalling effect recently reported for K dwarfs, in which the spin-down of K stars halts for over a gigayear when their rotation periods reach ≈10 days, rather than the continuous spin-down that G stars experience. These results imply that exoplanets orbiting K dwarfs may experience a stronger UV environment than thought, weakening the case for K stars as hosts of potential “super-habitable” planets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the internal distribution of star formation efficiency in IRAS 08339+6517 (hereafter IRAS08), using ∼200 pc resolution CO(2 − 1) observations from NOEMA. The molecular gas depletion time changes by 2 orders-of-magnitude from disk-like values in the outer parts to less than 10<jats:sup>8</jats:sup> yr inside the half-light radius. This translates to a star formation efficiency per freefall time that also changes by 2 orders-of-magnitude, reaching 50%–100%, different than local spiral galaxies and the typical assumption of constant, low star formation efficiencies. Our target is a compact, massive disk galaxy that has a star formation rate 10× above the <jats:italic>z</jats:italic> = 0 main sequence; Toomre <jats:italic>Q</jats:italic> ≈ 0.5−0.7 and high gas velocity dispersion (<jats:italic>σ</jats:italic> <jats:sub>mol</jats:sub> ≈ 25 km s<jats:sup>−1</jats:sup>). We find that IRAS08 is similar to other rotating, starburst galaxies from the literature in the resolved <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{\mathrm{SFR}}\propto {{\rm{\Sigma }}}_{\mathrm{mol}}^{N}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>SFR</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>mol</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac51c8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> relation. By combining resolved literature studies we find that the distance from the main sequence is a strong indicator of the Kennicutt-Schmidt power-law slope, with slopes of <jats:italic>N</jats:italic> ≈ 1.6 for starbursts from 100 to 10<jats:sup>4</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> pc<jats:sup>−2</jats:sup>. Our target is consistent with a scenario in which violent disk instabilities drive rapid inflows of gas. It has low values of Toomre-<jats:italic>Q</jats:italic>, and also at all radii, the inflow timescale of the gas is less than the depletion time, which is consistent with the flat metallicity gradients in IRAS08. We consider these results in light of popular star formation theories; in general observations of IRAS08 find the most tension with theories in which star formation efficiency is a constant. Our results argue for the need of high-spatial-resolution CO observations for a larger number of similar targets.</jats:p>