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<jats:title>Abstract</jats:title> <jats:p>Measurements of the atomic hydrogen (H<jats:sc>i</jats:sc>) properties of high-redshift galaxies are critical to understanding the decline in the star formation rate (SFR) density of the universe after its peak ≈8–11 Gyr ago. Here, we use ≈510 hr of observations with the upgraded Giant Metrewave Radio Telescope to measure the dependence of the average H<jats:sc>i</jats:sc> mass of star-forming galaxies at <jats:italic>z</jats:italic> = 0.74–1.45 on their average stellar mass and redshift by stacking their H<jats:sc>i</jats:sc> 21 cm emission signals. We divide our sample of 11,419 main-sequence galaxies at <jats:italic>z</jats:italic> = 0.74–1.45 into two stellar-mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) subsamples, with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> &gt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> &lt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and obtain clear detections, at &gt;4.6<jats:italic>σ</jats:italic> significance, of the stacked H<jats:sc>i</jats:sc> 21 cm emission in both subsamples. We find that galaxies with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> &gt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which dominate the decline in the cosmic SFR density at <jats:italic>z</jats:italic> ≲ 1, have H<jats:sc>i</jats:sc> reservoirs that can sustain their SFRs for only a short period, 0.86 ± 0.20 Gyr, unless their H<jats:sc>i</jats:sc> is replenished via accretion. We also stack the H<jats:sc>i</jats:sc> 21 cm emission from galaxies in two redshift subsamples, at <jats:italic>z</jats:italic> = 0.74–1.25 and <jats:italic>z</jats:italic> = 1.25–1.45, again obtaining clear detections of the stacked H<jats:sc>i</jats:sc> 21 cm emission signals, at &gt;5.2<jats:italic>σ</jats:italic> significance in both subsamples. We find that the average H<jats:sc>i</jats:sc> mass of galaxies with 〈<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>〉 ≈ 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> declines steeply over a period of ≈1 billion years, from (33.6 ± 6.4) × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at 〈<jats:italic>z</jats:italic>〉 ≈ 1.3 to (10.6 ± 1.9) × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at 〈<jats:italic>z</jats:italic>〉 ≈ 1.0, i.e., by a factor ≳3. We thus find direct evidence that accretion of H<jats:sc>i</jats:sc> onto star-forming galaxies at <jats:italic>z</jats:italic> ≈ 1 is insufficient to replenish their H<jats:sc>i</jats:sc> reservoirs and sustain their SFRs, thus resulting in the decline in the cosmic SFR density 8 billion years ago.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Soft X-ray emissions from solar wind charge exchange (SWCX) are applied in a recently developed approach to study the magnetosphere using panoramic soft X-ray imaging. This study represents the first attempt to distinguish magnetospheric SWCX emissions observed by XMM-Newton during the impact of an interplanetary coronal mass ejection (ICME) and its driven sheath on Earth. In addition, data from the Advanced Composition Explorer (ACE) were available during this same observational period, which is rare in previous studies. Results showed that SWCX emissions peaked during the ICME at approximately 2.3 times the mean of the observation period, although the solar wind flux decreased to a much lower level. A comparison of spectral results with ion data probed by ACE revealed that high ionization states in the ICME effectively enhanced line emission intensity for heavy ions (e.g., Ne, Mg, and Al). Thus, despite a low proton flux, elevated high-valence ion abundance in the ICME favors magnetospheric soft X-ray observations. Furthermore, the fitted X-ray flux of ion line emissions was consistent with elemental abundance ratios determined in situ by ACE, particularly for C<jats:sup>5+</jats:sup>, C<jats:sup>6+</jats:sup>, Ne<jats:sup>9+</jats:sup>, Mg<jats:sup>11+</jats:sup>, and Mg<jats:sup>12+</jats:sup>. This confirms the viability of spectral diagnosis of SWCX emissions as a new method for remotely analyzing high-state ion distributions in solar wind. A time-correlated or two-stage efficiency factor is further suggested to better estimate X-ray intensity during an ICME impact, which was ∼1.7 times higher in the ICME than in the sheath.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ultra-diffuse galaxies that contain a large sample of globular clusters (GCs) offer an opportunity to test the predictions of galactic dynamics theory. NGC5846-UDG1 is an excellent example, with a high-quality sample of dozens of GC candidates. We show that the observed distribution of GCs in NGC5846-UDG1 is suggestive of mass segregation induced by gravitational dynamical friction. We present simple analytic calculations, backed by a series of numerical simulations, that naturally explain the observed present-day pattern of GC masses and radial positions. Subject to some assumptions on the GC population at birth, the analysis supports the possibility that NGC5846-UDG1 resides in a massive dark matter halo. This is an example for the use of GC-rich systems as dynamical (in addition to kinematical) tracers of dark matter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine the radial evolution of correlation lengths perpendicular (<jats:inline-formula> <jats:tex-math> <?CDATA ${\lambda }_{C}^{\perp }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊥</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac73fdieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and parallel (<jats:inline-formula> <jats:tex-math> <?CDATA ${\lambda }_{C}^{\parallel }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac73fdieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) to the magnetic-field direction, computed from solar wind magnetic-field data measured by Parker Solar Probe (PSP) during its first eight orbits, Helios 1, Advanced Composition Explorer (ACE), WIND, and Voyager 1 spacecraft. Correlation lengths are grouped by an interval’s alignment angle; the angle between the magnetic-field and solar wind velocity vectors (Θ<jats:sub>BV</jats:sub>). Parallel and perpendicular angular channels correspond to angles 0° &lt; Θ<jats:sub>BV</jats:sub> &lt; 40° and 50° &lt; Θ<jats:sub>BV</jats:sub> &lt; 90°, respectively. We observe an anisotropy in the inner heliosphere within 0.40 au, with <jats:inline-formula> <jats:tex-math> <?CDATA ${\lambda }_{C}^{\parallel }/{\lambda }_{C}^{\perp }\approx 0.75$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msubsup> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊥</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>≈</mml:mo> <mml:mn>0.75</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac73fdieqn3.gif" xlink:type="simple" /> </jats:inline-formula> at 0.10 au. This anisotropy reduces with increasing heliocentric distance and the correlation lengths roughly isotropize within 1 au. Results from ACE and WIND support a reversal of the anisotropy, such that <jats:inline-formula> <jats:tex-math> <?CDATA ${\lambda }_{C}^{\parallel }/{\lambda }_{C}^{\perp }\approx 1.29$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">∥</mml:mo> </mml:mrow> </mml:msubsup> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊥</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>≈</mml:mo> <mml:mn>1.29</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac73fdieqn4.gif" xlink:type="simple" /> </jats:inline-formula> at 1 au. The ratio does not appear to change significantly beyond 1 au, although the small number of parallel intervals in the Voyager data set precludes unambiguous conclusions from being drawn. This study provides insights regarding the radial evolution of the large, most energetic interacting turbulent fluctuations in the heliosphere. We also emphasize the importance of tracking the changes in sampling direction in PSP measurements as the spacecraft approaches the Sun, when using these data to study the radial evolution of turbulence. This can prove to be vital in understanding the more complex dynamics of the solar wind in the inner heliosphere and can assist in improving related simulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A leading theoretical expectation for the final stages of planet formation is that disk migration should naturally drive orbits into chains of mean motion resonances (MMRs). In order to explain the dearth of MMR chains observed at Gyr ages (&lt;1%), this picture requires such configurations to destabilize and scramble period ratios following disk dispersal. Strikingly, the only two known stars with three or more planets younger than ≲100 Myr, HR 8799 and V1298 Tau, have been suggested to be in such MMR chains, given the orbits’ near-integer period ratios. We incorporate recent transit and radial velocity (RV) observations of the V1298 Tau system, and investigate constraints on the system’s orbital architecture imposed by requiring dynamical stability on timescales much shorter than the system’s age. We show that the recent RV mass measurement of V1298 Tau <jats:italic>b</jats:italic> places it within a factor of 2 of the instability limit, and that this allows us to set significantly lower limits on the eccentricity (<jats:italic>e</jats:italic> <jats:sub> <jats:italic>b</jats:italic> </jats:sub> ≤0.17 at 99.7% confidence). Additionally, we rule out a resonant chain configuration for V1298 Tau at ≳99% confidence. Thus, if the ∼23 Myr old V1298 Tau system did form as a resonant chain, it must have undergone instability and rearrangement shortly after disk dispersal. We expect that similar stability constrained characterization of future young multiplanet systems will be valuable in informing planet formation models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present early-time photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2021aefx. The early-time <jats:italic>u</jats:italic>-band light curve shows an excess flux when compared to normal SNe Ia. We suggest that the early excess blue flux may be due to a rapid change in spectral velocity in the first few days post explosion, produced by the emission of the Ca <jats:sc>ii</jats:sc> H&amp;K feature passing from the <jats:italic>u</jats:italic> to the <jats:italic>B</jats:italic> bands on the timescale of a few days. This effect could be dominant for all SNe Ia that have broad absorption features and early-time velocities over 25,000 km s<jats:sup>−1</jats:sup>. It is likely to be one of the main causes of early excess <jats:italic>u</jats:italic>-band flux in SNe Ia that have early-time high velocities. This effect may also be dominant in the UV filters, as well as in places where the SN spectral energy distribution is quickly rising to longer wavelengths. The rapid change in velocity can only produce a monotonic change (in flux-space) in the <jats:italic>u </jats:italic>band. For objects that explode at lower velocities, and have a more structured shape in the early excess emission, there must also be an additional parameter producing the early-time diversity. More early-time observations, in particular early spectra, are required to determine how prominent this effect is within SNe Ia.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Understanding how matter behaves at the highest densities and temperatures is a major open problem in both nuclear physics and relativistic astrophysics. Our understanding of such behavior is often encapsulated in the so-called high-temperature nuclear equation of state (EOS), which influences compact binary mergers, core-collapse supernovae, and other phenomena. Our focus is on the type (either black hole or neutron star) and mass of the remnant of the core collapse of a massive star. For each six candidates of equations of state, we use a very large suite of spherically symmetric supernova models to generate a sample of synthetic populations of such remnants. We then compare these synthetic populations to the observed remnant population. Our study provides a novel constraint on the high-temperature nuclear EOS and describes which EOS candidates are more or less favored by an information-theoretic metric.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present ALMA 1.3 mm observations of the HD 53143 debris disk—the first infrared or millimeter image produced of this ∼1 Gyr old solar analog. Previous HST STIS coronagraphic imaging did not detect flux along the minor axis of the disk, which could suggest a face-on geometry with two clumps of dust. These ALMA observations reveal a disk with a strikingly different structure. In order to fit models to the millimeter visibilities and constrain the uncertainties on the disk parameters, we adopt a Markov Chain Monte Carlo approach. This is the most eccentric debris disk observed to date with a forced eccentricity of 0.21 ± 0.02, nearly twice that of the Fomalhaut debris disk, and also displays an apocenter glow. Although this eccentric model fits the outer debris disk well, significant interior residuals remain, which may suggest a possible edge-on inner disk, which remains unresolved in these observations. Combined with the observed structure difference between HST and ALMA, these results suggest a potential previous scattering event or dynamical instability in this system. We also note that the stellar flux changes considerably over the course of our observations, suggesting flaring at millimeter wavelengths. Using simultaneous TESS observations, we determine the stellar rotation period to be 9.6 ± 0.1 days.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present evidence that it is unlikely that the streaming instability (SI) can form planetesimals from millimeter grains inside axisymmetric pressure bumps. We conducted the largest simulation of the SI so far (7 million CPU hours), consisting of a large slice of the disk with millimeter grains, a solar-like dust-to-gas ratio (<jats:italic>Z</jats:italic> = 0.01), and the largest pressure bump that does not cause gravitational instability (GI) in the particle layer. We used a high resolution of 1000/<jats:italic>H</jats:italic> to resolve as many SI unstable modes as possible. The simulation produced a long-lived particle overdensity far exceeding the SI criteria (i.e., a critical solid abundance to headwind parameter ratio <jats:italic>Z</jats:italic>/Π) where strong clumping would occur if these conditions were present over an extended region of the disk; yet we observed none. The likely reason is that the time it takes particles to cross the high-<jats:italic>Z</jats:italic>/Π region (<jats:italic>t</jats:italic> <jats:sub>cross</jats:sub>) is shorter than the growth timescale of the SI (<jats:italic>t</jats:italic> <jats:sub>grow</jats:sub>). We propose an added criterion for planetesimal formation by the SI—that <jats:italic>t</jats:italic> <jats:sub>cross</jats:sub> &gt; <jats:italic>t</jats:italic> <jats:sub>grow</jats:sub>. We show that any bump larger than the one in this run would form planetesimals by the GI instead of the SI. Our results significantly restrict the pathways to planet formation: either protoplanetary disks regularly form grains larger than 1 mm, or planetesimals do not form by the SI in axisymmetric pressure bumps. Since bumps large enough to induce the GI are likely Rossby-wave unstable, we propose that millimeter grains may only form planetesimals in vortices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Green Pea galaxies are low-redshift starburst dwarf galaxies, with properties similar to those of the high-redshift galaxies that reionized the universe. We report the first mapping of the spatial distribution of atomic hydrogen (H<jats:sc>i</jats:sc>) in and around a Green Pea, GP J0213+0056 at <jats:italic>z</jats:italic> = 0.0399, using the Giant Metrewave Radio Telescope (GMRT). Like many Green Peas, GP J0213+0056 shows strong H<jats:sc>i</jats:sc> 21 cm emission in single-dish spectroscopy, strong Ly<jats:italic>α</jats:italic> emission, and a high [O<jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic>5007 Å/[O<jats:sc>ii</jats:sc>]<jats:italic>λ</jats:italic>3727 Å luminosity ratio, O32 ≈ 8.8, consistent with a high leakage of Lyman-continuum radiation. Our GMRT H<jats:sc>i</jats:sc> 21 cm images show that the H<jats:sc>i</jats:sc> 21 cm emission in the field of GP J0213+0056 arises from an extended broken-ring structure around the Green Pea, with the strongest emission coming from a region between GP J0213+0056 and a companion galaxy lying ≈4.7 kpc away, and little H<jats:sc>i</jats:sc> 21 cm emission coming from the Green Pea itself. We find that the merger between GP J0213+0056 and its companion is likely to have triggered the starburst, and led to a disturbed H<jats:sc>i</jats:sc> spatial and velocity distribution, which in turn allowed Ly<jats:italic>α</jats:italic> (and, possibly, Lyman-continuum) emission to escape the Green Pea. Our results suggest that such mergers, and the resulting holes in the H<jats:sc>i</jats:sc> distribution, are a natural way to explain the tension between the requirements of cold gas to fuel the starburst and the observed leakage of Ly<jats:italic>α</jats:italic> and Lyman-continuum emission in Green Pea galaxies and their high-redshift counterparts.</jats:p>