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<jats:title>Abstract</jats:title> <jats:p>Stellar bow shocks are observed in a variety of interstellar environments and shaped by the conditions of gas in the interstellar medium (ISM). In situ measurements of turbulent density fluctuations near stellar bow shocks are only achievable with a few observational probes, including H<jats:italic>α</jats:italic>-emitting bow shocks and the Voyager Interstellar Mission (VIM). In this paper, we examine density variations around the Guitar Nebula, an H<jats:italic>α</jats:italic> bow shock associated with PSR B2224+65, in tandem with density variations probed by VIM near the boundary of the solar wind and ISM. High-resolution Hubble Space Telescope observations of the Guitar Nebula taken between 1994 and 2006 trace density variations over scales from hundreds to thousands of au, while VIM density measurements made with the Voyager 1 Plasma Wave System constrain variations from thousands of meters to tens of au. The power spectrum of density fluctuations constrains the amplitude of the turbulence wavenumber spectrum near the Guitar Nebula to <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}{C}_{{\rm{n}}}^{2}=-0.8\pm 0.2$?> </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:msubsup> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>0.8</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.2</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2b28ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> m<jats:sup>−20/3</jats:sup> and for the very local ISM probed by Voyager to <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}{C}_{{\rm{n}}}^{2}=-1.57\pm 0.02$?> </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:msubsup> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1.57</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.02</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2b28ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> m<jats:sup>−20/3</jats:sup>. Spectral amplitudes obtained from multiepoch observations of four other H<jats:italic>α</jats:italic> bow shocks also show significant enhancements from values that are considered typical for the diffuse, warm ionized medium, suggesting that density fluctuations near these bow shocks may be amplified by shock interactions with the surrounding medium or selection effects that favor H<jats:italic>α</jats:italic> emission from bow shocks embedded in denser media.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The youngest Galactic supernova remnant, G1.9+0.3, probably the result of a Type Ia supernova, shows surprising anomalies in the distribution of its ejecta in space and velocity. In particular, high-velocity shocked iron is seen in several locations far from the remnant center, in some cases beyond prominent silicon and sulfur emission. These asymmetries strongly suggest a highly asymmetric explosion. We present high-resolution hydrodynamic simulations in two and three dimensions of the evolution from ages of 100 s to hundreds of years of two asymmetric Type Ia models, expanding into a uniform medium. At the age of G1.9+0.3 (about 100 yr), our 2D model shows almost no iron shocked to become visible in X-rays. Only in a much higher-density environment could significant iron be shocked, at which time the model's expansion speed is completely inconsistent with the observations of G1.9+0.3. Our 3D model, evolving the most asymmetric of a suite of Type Ia supernova models from Seitenzahl et al. (2013), shows some features resembling G1.9+0.3. We characterize its evolution with images of composition in three classes: C and O, intermediate-mass elements (IMEs), and iron-group elements (IGEs). From ages of 13 to 1800 yr, we follow the evolution of the highly asymmetric initial remnant as the explosion asymmetries decrease in relative strength, to be replaced by asymmetries due to evolutionary hydrodynamic instabilities. At an age of about 100 yr, our 3D model has comparable shocked masses of C+O, IMEs, and IGEs, with about 0.03 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> each. Evolutionary changes appear to be rapid enough that continued monitoring with the Chandra X-ray Observatory may show significant variations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first analysis of internal coronal mass ejection (CME) structure observed very close to the Sun by the Wide-field Imager for Solar PRobe (WISPR) instrument on board the Parker Solar Probe (PSP). The transient studied here is a CME observed during PSP’s second perihelion passage on 2019 April 2, when PSP was only 40 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> from the Sun. The CME was also well observed from 1 au by the STEREO-A spacecraft, which tracks the event all the way from the Sun to 1 au. However, PSP/WISPR observes internal structure not apparent in the images from 1 au. In particular, two linear features are observed, one bright and one dark. We model these features as two loops within the CME flux rope (FR) channel. The loops can be interpreted as bundles of field lines, with the brightness of the bright loop indicative of lots of mass being loaded into those field lines, and with the dark loop being devoid of such mass loading. It is possible that these loops are actually representative of two independent FR structures within the overall CME outline.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The ZrO B<jats:sup>1</jats:sup>Π—X<jats:sup>1</jats:sup>Σ<jats:sup>+</jats:sup> transition is an important opacity source in the near-infrared and optical spectrum of S-type stars. The 0–0, 0–1, 0–2, 1–0, 1–2, 1–3, 2–0, 2–1, 2–3, 2–4, 3–1, 3–4, and 4–2 bands of the <jats:sup>90</jats:sup>Zr<jats:sup>16</jats:sup>O B<jats:sup>1</jats:sup>Π—X<jats:sup>1</jats:sup>Σ<jats:sup>+</jats:sup> transition are reanalyzed using a high-temperature (2390 K) high-resolution (0.04 cm<jats:sup>−1</jats:sup>) emission spectrum collected at the National Solar Observatory (Kitt Peak). A modern spectroscopic analysis was performed using the PGOPHER program to provide updated spectroscopic constants and to produce a high-precision line list with line strengths based on an ab initio calculation of the transition dipole moment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the role of atomic hydrogen (H <jats:sc>i</jats:sc>) in regulating the size growth of local galaxies. The size of a galaxy, <jats:italic>D</jats:italic> <jats:sub> <jats:italic>r</jats:italic>,25</jats:sub>, is characterized by the diameter at which the <jats:italic>r</jats:italic>-band surface brightness reaches <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{{\rm{r}}}=25.0\,\mathrm{mag}\,{\mathrm{arcsec}}^{-2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>25.0</mml:mn> <mml:mspace width="0.25em" /> <mml:mi>mag</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>arcsec</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2a37ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. We find that the positions of galaxies in the size (<jats:italic>D</jats:italic> <jats:sub> <jats:italic>r</jats:italic>,25</jats:sub>)−stellar-mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) plane strongly depend on their H <jats:sc>i</jats:sc>-to-stellar-mass ratio (<jats:italic>M</jats:italic> <jats:sub>H <jats:sc>i</jats:sc> </jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>). In the H <jats:sc>i</jats:sc>−rich regime, galaxies that are richer in H <jats:sc>i </jats:sc>tend to have larger sizes. Such a trend is not seen in the H <jats:sc>i</jats:sc>–poor regime, suggesting that size growth is barely affected by the H <jats:sc>i</jats:sc> content when it has decreased to a sufficiently low level. An investigation of the relations between size, <jats:italic>M</jats:italic> <jats:sub>H I</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>, and star formation rate (SFR) suggests that size is more intrinsically linked with <jats:italic>M</jats:italic> <jats:sub>H I</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>, rather than SFR. We further examine the H <jats:sc>i</jats:sc>-to-stellar-disk size ratio (<jats:italic>D</jats:italic> <jats:sub>H I</jats:sub>/<jats:italic>D</jats:italic> <jats:sub> <jats:italic>r</jats:italic>,25</jats:sub>) of galaxies and find that at log(<jats:italic>M</jats:italic> <jats:sub>H I</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) &gt; −0.7, <jats:italic>D</jats:italic> <jats:sub>H I</jats:sub>/<jats:italic>D</jats:italic> <jats:sub> <jats:italic>r</jats:italic>,25</jats:sub> is weakly correlated with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>. These findings support a picture in which the H <jats:sc>i</jats:sc>−rich galaxies live in an inside-out disk-growing phase regulated by gas accretion and star formation. The angular momentum of the accreted materials is probably the key parameter in shaping the size of a H <jats:sc>i</jats:sc>−rich galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It has been proposed that the filament environment is closely connected to the pre-processing of galaxies, where their properties may have been changed by environmental effects in the filament before they fell into the galaxy cluster. We present the chemical properties of star-forming dwarf galaxies (SFDGs) in five filamentary structures (Virgo III, Leo Minor, Leo II A, Leo II B, and Canes Venatici) around the Virgo cluster using the Sloan Digital Sky Survey optical spectroscopic data and Galaxy Evolution Explorer ultraviolet photometric data. We investigate the relationship between stellar mass, gas-phase metallicity, and specific star formation rate (sSFR) of the SFDGs in the Virgo filaments in comparison to those in the Virgo cluster and field. We find that, at a given stellar mass, SFDGs in the Virgo filaments show lower metallicity and higher sSFR than those in the Virgo cluster on average. We observe that SFDGs in the Virgo III filament show enhanced metallicities and suppressed star formation activities comparable to those in the Virgo cluster, whereas SFDGs in the other four filaments exhibit similar properties to the field counterparts. Moreover, about half of the galaxies in the Virgo III filament are found to be morphologically transitional dwarf galaxies that are supposed to be on the way to transforming into quiescent dwarf early-type galaxies. Based on the analysis of the galaxy perturbation parameter, we propose that the local environment represented by the galaxy interactions might be responsible for the contrasting features in chemical pre-processing found in the Virgo filaments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The MAMMOTH-1 nebula at <jats:italic>z</jats:italic> = 2.317 is an enormous Ly<jats:italic>α</jats:italic> nebula (ELAN) extending to a ∼440 kpc scale at the center of the extreme galaxy overdensity BOSS 1441. In this paper, we present observations of the CO(3 − 2) and 250 GHz dust-continuum emission from MAMMOTH-1 using the IRAM NOrthern Extended Millimeter Array. Our observations show that CO(3 − 2) emission in this ELAN has not extended widespread emission into the circum- and inter-galactic media. We also find a remarkable concentration of six massive galaxies in CO(3 − 2) emission in the central ∼100 kpc region of the ELAN. Their velocity dispersions suggest a total halo mass of <jats:italic>M</jats:italic> <jats:sub>200<jats:italic>c</jats:italic> </jats:sub> ∼ 10<jats:sup>13.1</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, marking a possible protocluster core associated with the ELAN. The peak position of the CO(3 − 2) line emission from the obscured AGN is consistent with the location of the intensity peak of MAMMOTH-1 in the rest-frame UV band. Its luminosity line ratio between the CO(3 − 2) and CO(1 − 0)<jats:italic>r</jats:italic> <jats:sub>3,1</jats:sub> is 0.61 ± 0.17. The other five galaxies have CO(3 − 2) luminosities in the range of (2.1–7.1) × 10<jats:sup>9</jats:sup> K km s<jats:sup>−1</jats:sup> pc<jats:sup>2</jats:sup>, with the star-formation rates derived from the 250 GHz continuum of (&lt;36)–224 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. Follow-up spectroscopic observations will further confirm more member galaxies and improve the accuracy of the halo mass estimation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Due to the chaotic nature of planetary dynamics, there is a non-zero probability that Mercury’s orbit will become unstable in the future. Previous efforts have estimated the probability of this happening between 3 and 5 billion years in the future using a large number of direct numerical simulations with an <jats:italic>N</jats:italic>-body code, but were not able to obtain accurate estimates before 3 billion years in the future because Mercury instability events are too rare. In this paper we use a new rare-event sampling technique, Quantile Diffusion Monte Carlo (QDMC), to estimate that the probability of a Mercury instability event in the next 2 billion years is approximately 10<jats:sup>−4</jats:sup> in the REBOUND <jats:italic>N</jats:italic>-body code. We show that QDMC provides unbiased probability estimates at a computational cost of up to 100 times less than direct numerical simulation. QDMC is easy to implement and could be applied to many problems in planetary dynamics in which it is necessary to estimate the probability of a rare event.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Chinese CubeSat Mission, Gamma Ray Integrated Detectors (GRID), recently detected its first gamma-ray burst, GRB 210121A, which was jointly observed by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM). This burst is confirmed by several other missions, including Fermi and Insight-HXMT. We combined multimission observational data and performed a comprehensive analysis of the burst’s temporal and spectral properties. Our results show that the burst is relatively special in its high peak energy, thermal-like low-energy indices, and large fluence. By putting it to the <jats:italic>E</jats:italic> <jats:italic> <jats:sub>p</jats:sub> </jats:italic>–<jats:italic>E</jats:italic> <jats:sub> <jats:italic>γ</jats:italic>,iso</jats:sub> relation diagram with assumed distance, we found that this burst can be constrained at the redshift range of [0.3, 3.0]. The thermal spectral component is also confirmed by the direct fit of the physical models to the observed spectra. Interestingly, the physical photosphere model also constrained a redshift of <jats:italic>z</jats:italic> ∼ 0.3 for this burst, which helps us to identify a host galaxy candidate at such a distance within the location error box. Assuming that the host galaxy is real, we found that the burst can be best explained by the photosphere emission of a typical fireball with an initial radius of <jats:italic>r</jats:italic> <jats:sub>0</jats:sub> ∼ 3.2 × 10<jats:sup>7</jats:sup> cm.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical and near-infrared (NIR, <jats:italic>Y</jats:italic>-<jats:italic>, J</jats:italic>-<jats:italic>,</jats:italic> <jats:italic> H-</jats:italic>band) observations of 42 Type Ia supernovae (SNe Ia) discovered by the untargeted intermediate Palomar Transient Factory survey. This new data set covers a broad range of redshifts and host galaxy stellar masses, compared to previous SN Ia efforts in the NIR. We construct a sample, using also literature data at optical and NIR wavelengths, to examine claimed correlations between the host stellar masses and the Hubble diagram residuals. The SN magnitudes are corrected for host galaxy extinction using either a global total-to-selective extinction ratio, <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> = 2.0, for all SNe, or a best-fit <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> for each SN individually. Unlike previous studies that were based on a narrower range in host stellar mass, we do not find evidence for a “mass step,” between the color- and stretch-corrected peak <jats:italic>J</jats:italic> and <jats:italic>H</jats:italic> magnitudes for galaxies below and above <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({M}_{* }/{M}_{\odot })=10$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </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:mn>10</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2f9eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. However, the mass step remains significant (3<jats:italic>σ</jats:italic>) at optical wavelengths (<jats:italic>g</jats:italic>, <jats:italic>r</jats:italic>, <jats:italic>i</jats:italic>) when using a global <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>, but vanishes when each SN is corrected using their individual best-fit <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>. Our study confirms the benefits of the NIR SN Ia distance estimates, as these are largely exempted from the empirical corrections dominating the systematic uncertainties in the optical.</jats:p>