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<jats:title>Abstract</jats:title> <jats:p>Type Ia supernovae (SNe Ia) are believed to be a thermonuclear explosion of a white dwarf, but the mass of their progenitors is still an open problem. In near-Chandrasekhar-mass (near-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub>) models of SNe Ia, the central density reaches ≳10<jats:sup>9</jats:sup> g cm<jats:sup>−3</jats:sup>. The electron chemical potential becomes higher than the <jats:italic>Q</jats:italic>-values of electron capture (EC) transitions between <jats:italic>fp</jats:italic>-shell nuclei, so a portion of the available electrons is captured by iron group elements and thus neutron-rich isotopes are formed. Since EC reaction rates are sensitive to the density, the degree of neutronization is a key to distinguish near- and sub-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> models. In order to compare observations and theoretical models, an accurate treatment of EC reactions is necessary. In previous theoretical works, however, effects of electron screening on ECs are ignored. Screening lowers EC rates and thus leads to a higher electron fraction. We implement electron screening on ECs to calculate explosive SN Ia nucleosynthesis in a near-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> single degenerate model. It is found that some of neutron-rich nuclear abundances, namely, those of <jats:sup>46,48</jats:sup>Ca, <jats:sup>50</jats:sup>Ti, <jats:sup>54</jats:sup>Cr, <jats:sup>58</jats:sup>Fe, <jats:sup>64</jats:sup>Ni, and <jats:sup>67,70</jats:sup>Zn, decrease when screening effects on ECs are considered. Of these, <jats:sup>50</jats:sup>Ti, <jats:sup>54</jats:sup>Cr, and <jats:sup>58</jats:sup>Fe are particularly interesting because a significant portion of the solar abundance of these nuclei is presumed to originate from SNe Ia. We conclude that implementing the screening effect on ECs in modern SN Ia models is desirable to precisely calculate abundances of neutron-rich nuclides.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present SOFIA/FIFI-LS observations of the [C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H <jats:sc>i</jats:sc> data to compare [C <jats:sc>ii</jats:sc>] emission to dust properties, star formation rate (SFR), H<jats:sub>2</jats:sub>, and H <jats:sc>i</jats:sc> at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the [C <jats:sc>ii</jats:sc>] luminosity to arms, and 19% and 8% to the center and interarm region, respectively. [C <jats:sc>ii</jats:sc>]/TIR, [C <jats:sc>ii</jats:sc>]/CO, and [C <jats:sc>ii</jats:sc>]/PAH radial profiles are largely constant, but rise at large radii (≳ 8 kpc) and drop in the center (“[C <jats:sc>ii</jats:sc>] deficit”). This increase at large radii and the observed decline with the 70 <jats:italic>μ</jats:italic>m/100 <jats:italic>μ</jats:italic>m dust color are likely driven by radiation field hardness. We find a near proportional [C <jats:sc>ii</jats:sc>]–SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [C <jats:sc>ii</jats:sc>] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [C <jats:sc>ii</jats:sc>] as an H<jats:sub>2</jats:sub> and SFR tracer in such regimes. Finally, based on the observed [C <jats:sc>ii</jats:sc>] and CO radial profiles and different models, we find <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> to increase with radius, in line with the observed metallicity gradient. The low <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> (galaxy average ≲ 2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> pc<jats:sup>−2</jats:sup> (K km s<jats:sup>−1</jats:sup>)<jats:sup>−1</jats:sup>) and low [C <jats:sc>ii</jats:sc>]/CO ratios (∼400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We performed statistical analysis on the flare emission data to examine parameters related to the flare extreme-ultraviolet (EUV) spectra. This study used the data from the Geostationary Operational Environmental Satellite X-ray Sensors to determine the fundamental flare parameters. The relationship between soft X-ray data and EUV emission data observed by the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory (SDO) MEGS-A was investigated for 50 events. The results showed the hotter Fe line emissions have strong correlation with soft X-ray data in many cases. However, our statistical study revealed that EUV flare peak flux of Fe <jats:sc>xv</jats:sc>, Fe <jats:sc>xvi</jats:sc> and He <jats:sc>ii</jats:sc> lines have weak correlation with soft X-ray peak flux. In EUV line light curves, there was time difference in peak time, however the tendency to reach the peak in order from the hotter line to cooler line was not so clear. These results indicate that the temporal evolution of EUV emission can be roughly explained by soft X-ray data. However, the time changes of temperature and density distributions in the flare loop must be needed for accurate reproduction. Moreover, we compared the geometrical features of solar flares observed by the Atmospheric Imaging Assembly on board the SDO with the fundamental flare parameters for 32 events. The ribbon distance strongly correlated with both soft X-ray flare rise and decay times. This results indicate that the geometrical feature is essential parameter for predicting flare emission duration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine the properties of the circumgalactic medium (CGM) at low redshift in a range of simulated Milky Way mass halos. The sample is comprised of seven idealized simulations, an adaptive mesh refinement cosmological zoom-in simulation, and two groups of 50 halos with star-forming or quiescent galaxies taken from the TNG100 simulation. The simulations have very different setups, resolution, and feedback models, but are analyzed in a uniform manner. By comparing median radial profiles and mass distributions of CGM properties, we isolate key similarities and differences. In doing so, we advance the efforts of the Simulating Multiscale Astrophysics to Understand Galaxies project that aims to understand the inherently multiscale galaxy formation process. In the cosmological simulations, the CGM exhibits nearly flat temperature distributions, and broad pressure and radial velocity distributions. In the idealized simulations, similar distributions are found in the inner CGM (<jats:inline-formula> <jats:tex-math> <?CDATA $\lesssim 0.5\,{r}_{200{\rm{c}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbc6dieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) when strong galactic feedback models are employed, but the outer CGM (<jats:inline-formula> <jats:tex-math> <?CDATA $\gtrsim 0.5\,{r}_{200{\rm{c}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbc6dieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) has a much less prominent cold phase, and narrower pressure and velocity distributions even in models with strong feedback. This comparative analysis demonstrates the dominant role feedback plays in shaping the inner CGM and the increased importance of cosmological effects, such as nonspherical accretion and satellite galaxies, in the outer CGM. Furthermore, our findings highlight that, while cosmological simulations are required to capture the multiphase structure of the CGM at large radii, idealized simulations provide a robust framework to study how galactic feedback interacts with the inner CGM, and thereby provide a reliable avenue to constrain feedback prescriptions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The evolution of a pulsar wind nebula (PWN) depends on properties of the progenitor star, supernova, and surrounding environment. As some of these quantities are difficult to measure, reproducing the observed dynamical properties and spectral energy distribution (SED) with an evolutionary model is often the best approach to estimating their values. G21.5−0.9, powered by the pulsar J1833−1034, is a well observed PWN for which previous modeling efforts have struggled to reproduce the observed SED. In this study, we reanalyze archival infrared (IR; Herschel, Spitzer) and X-ray (Chandra, NuSTAR, Hitomi) observations. The similar morphology observed between IR line and continuum images of this source indicates that a significant portion of this emission is generated by surrounding dust and gas, and not synchrotron radiation from the PWN. Furthermore, we find that the broadband X-ray spectrum of this source is best described by a series of power laws fit over distinct energy bands. For all X-ray detectors, we find significant softening and decreasing unabsorbed flux in higher energy bands. Our model for the evolution of a PWN is able to reproduce the properties of this source when the supernova ejecta has a low initial kinetic energy <jats:italic>E</jats:italic> <jats:sub>sn</jats:sub> ≈ 1.2 × 10<jats:sup>50</jats:sup> erg and the spectrum of particles injected into the PWN at the termination shock is softer at low energies. Lastly, our hydrodynamical modeling of the supernova remnant can reproduce its morphology if there is a significant increase in the density of the ambient medium ∼1.8 pc north of the explosion center.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The primary method for inferring the stellar mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) of a galaxy is through spectral energy distribution (SED) modeling. However, the technique rests on assumptions such as the galaxy star formation history (SFH) and dust attenuation law that can severely impact the accuracy of derived physical properties from SED modeling. Here we examine the effect that the assumed SFH has on the stellar properties inferred from SED fitting by ground-truthing them against mock observations of high-resolution cosmological hydrodynamic galaxy formation simulations. Classically, SFHs are modeled with simplified parameterized functional forms, but these forms are unlikely to capture the true diversity of galaxy SFHs and may impose systematic biases with underreported uncertainties on results. We demonstrate that flexible nonparametric SFHs outperform traditional parametric forms in capturing variations in galaxy SFHs and, as a result, lead to significantly improved stellar masses in SED fitting. We find a decrease in the average bias of 0.4 dex with a delayed-<jats:italic>τ</jats:italic> model to a bias under 0.1 dex for the nonparametric model, though this is heavily dependent on the choice of prior for the nonparametric model. Similarly, using nonparametric SFHs in SED fitting results in increased accuracy in recovered galaxy star formation rates and stellar ages.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of the ejecta from the final flash (FF) of helium shell burning in Sakurai’s Object (V4334 Sgr) are presented for 2015–2019, a period ∼20–24 yr after discovery. Adaptive optics images at <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> trace the expanding debris. While most of the ejecta mass is in ∼200 K dust, a small fraction, ∼0.4%, of the dust mass is at ∼760 K. The 760 K continuum dominates the near-IR images. Spatial-spectral images in He <jats:sc>i</jats:sc> 10830 Å show an ∼16 diameter bipolar planetary nebula at position angle 21° ± 5° with the SW moving toward us and the NE moving away. Seen in integrated light, the nebula is nearly circular. Near-IR continuum images show ejecta moving radially away from a bright central point source. High-resolution mid-IR spectra reveal molecular hydrocarbon lines with an expansion velocity of 270 ± 5 km s<jats:sup>−1</jats:sup> seen in absorption against the dust continuum. The hydrocarbons originate in material produced in the FF. The bipolar nebula and debris clouds are discussed in the context of a highly inclined disk model. The proper motion has been measured placing V4334 Sgr in the thick disk population. There is no evidence that a hot white dwarf Wolf–Rayet ([WR]) wind has emerged; no [WR] spectral features were detected. The possibility of a binary companion involved in the evolution is discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We characterize the relaxation state of galaxy systems by providing an assessment of the reliability of the photometric and spectroscopic probe via the semianalytic galaxy evolution model. We quantify the correlations between the dynamical age of simuglated galaxy groups and popular proxies of halo relaxation in observation, which are mainly either spectroscopic or photometric. We find the photometric indicators demonstrate a stronger correlation with the dynamical relaxation of galaxy groups compared to the spectroscopic probes. We take advantage of the Anderson Darling statistic (<jats:italic>A</jats:italic> <jats:sup>2</jats:sup>) and the velocity segregation (<jats:inline-formula> <jats:tex-math> <?CDATA $\overline{{\rm{\Delta }}V}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd47ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) as our spectroscopic indicators, and use the luminosity gap (Δ<jats:italic>m</jats:italic> <jats:sub>12</jats:sub>) and the luminosity decentering (<jats:italic>D</jats:italic> <jats:sub>offset</jats:sub>) as photometric ones. First, we find that a combination of Δ<jats:italic>m</jats:italic> <jats:sub>12</jats:sub> and <jats:italic>D</jats:italic> <jats:sub>offset</jats:sub> evaluated by a bivariant relation (<jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{B}}=0.04\times {\rm{\Delta }}{m}_{12}-0.11\times \mathrm{Log}({D}_{\mathrm{off}-\mathrm{set}})+0.28$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd47ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) shows a good correlation with the dynamical age compared to all other indicators. Second, by using the observational X-ray surface brightness map, we show that the bivariant relation brings about some acceptable correlations with X-ray proxies. These correlations are as well as the correlations between <jats:italic>A</jats:italic> <jats:sup>2</jats:sup> and X-ray proxies, offering a reliable yet fast and economical method of quantifying the relaxation of galaxy systems. This study demonstrates that using photometric data to determine the relaxation status of a group will lead to some promising results that are comparable with the more expensive spectroscopic counterpart.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We estimated the dynamical masses of 115 early-type galaxies (ETGs) by analyzing the dynamics of satellite and companion galaxies of these ETGs. We selected galaxies with absolute magnitudes between −22 and −25 in the <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>-band from the Extragalactic Distance Database. We also selected 216 spiral galaxies for comparison. We employed a simple model to simulate the observed dynamical mass from satellite galaxies at various distances. Our simulations showed that the dynamical masses derived from satellite galaxies with elliptical orbits would be smaller than those with circular orbits even though they contain the same dark mass halos. Therefore, relationships between the observed <jats:italic>M</jats:italic> <jats:sub>dyn</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>b</jats:sub> distributions and distances would depend on orbital shapes. From the relationships between our observed <jats:italic>M</jats:italic> <jats:sub>dyn</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>b</jats:sub> distributions and distances, we suggest that the satellite galaxies of the ETGs have relatively more elliptical orbits than those of the spiral galaxies and the <jats:italic>M</jats:italic> <jats:sub>dyn</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>b</jats:sub> of the ETGs are greater than those of the spiral galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the effect of variations in dust size distribution and composition on the correlation between the spectral shape of extinction (parameterized by <jats:italic>R</jats:italic> <jats:sub>V</jats:sub>) and far-infrared dust emissivity (parameterized by the power-law index <jats:italic>β</jats:italic>). Starting from the size distribution models proposed by Weingartner &amp; Draine, using the dust absorption and emission properties derived by Laor &amp; Draine for carbonaceous and silicate grains, and by Li &amp; Draine for polycyclic aromatic hydrocarbon grains, we calculate the extinction and compare it with the reddening vector derived by Schlafly et al. An optimizer and an Markov chain Monte Carlo method are used to explore the space of available parameters for the size distributions. We find that larger grains are correlated with high <jats:italic>R</jats:italic> <jats:sub>V</jats:sub>. However, this trend is not enough to explain the emission-extinction correlation observed by Schlafly et al. For the <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> − <jats:italic>β</jats:italic> correlation to arise, we need to impose explicit priors for the carbonaceous and silicate volume priors as functions of <jats:italic>R</jats:italic> <jats:sub>V</jats:sub>. The results show that a composition with higher ratio of carbonaceous to silicate grains leads to higher <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> and lower <jats:italic>β</jats:italic>. A relation between <jats:italic>E</jats:italic>(B − V)/<jats:italic>τ</jats:italic> <jats:sub>353</jats:sub> and <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> is apparent, with possible consequences for the recalibration of emission-based dust maps as a function of <jats:italic>R</jats:italic> <jats:sub>V</jats:sub>.</jats:p>