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<jats:title>Abstract</jats:title> <jats:p>Dust polarization induced by aligned grains is widely used to study magnetic fields in various astrophysical environments. However, the question of to what optical depth grain alignment still exists in a dense molecular cloud (MC) is unclear. In this paper, we derive analytical formulae for the minimum size of aligned grains (<jats:italic>a</jats:italic> <jats:sub>align</jats:sub>) and rotational disruption (<jats:italic>a</jats:italic> <jats:sub>disr</jats:sub>) by RAdiative Torques (RATs) as a function of the local physical parameters within MCs. We first find the analytical approximations for the radiation strength and mean wavelength of the attenuated radiation field in a dense MC with and without embedded stars, and then derive analytical formulae for <jats:italic>a</jats:italic> <jats:sub>align</jats:sub> and <jats:italic>a</jats:italic> <jats:sub>disr</jats:sub> as functions of the visual extinction <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> and gas density. We find that, within a starless core of density <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{{\rm{H}}}\sim {10}^{5}\,{\mathrm{cm}}^{-3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd54fieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, grains of size <jats:inline-formula> <jats:tex-math> <?CDATA $a\lt 0.25\,\mu {\rm{m}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd54fieqn2.gif" xlink:type="simple" /> </jats:inline-formula> can be aligned at <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ∼ 5 by RATs, whereas micron-sized grains can still be aligned at <jats:inline-formula> <jats:tex-math> <?CDATA ${A}_{V}\sim 50$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd54fieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. The increase in <jats:italic>a</jats:italic> <jats:sub>align</jats:sub> with <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> can explain the presence of polarization holes observed toward starless cores. For MCs with an embedded protostar, the efficiency of both alignment and rotational disruption increases toward the protostar due to the increasing radiation strength. Such a disruption effect results in the decrease of the polarization degree with <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> or emission intensity, reproducing the popular polarization holes observed toward the location of protostars. Finally, we derive the formula for the maximum <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> where grain alignment still exists in a starless core, and we discuss its potential for constraining grain growth.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ly<jats:italic>α</jats:italic> emitting galaxies are powerful tools to probe the late stages of cosmic reionization. The observed sudden drop in Ly<jats:italic>α</jats:italic> fraction at <jats:italic>z</jats:italic> &gt; 6 is often interpreted as a sign of reionization, since the intergalactic medium (IGM) is more neutral and opaque to Ly<jats:italic>α</jats:italic> photons. Crucially, this interpretation of the observations is only valid under the assumption that galaxies themselves experience a minimal evolution at these epochs. By modeling Ly<jats:italic>α</jats:italic> radiative transfer effects in and around galaxies, we examine whether a change in the galactic properties can reproduce the observed drop in the Ly<jats:italic>α</jats:italic> fraction. We find that an increase in the galactic neutral hydrogen content or a reduction in the outflow velocity toward higher redshift both lead to a lower Ly<jats:italic>α</jats:italic> escape fraction, and can thus mimic an increasing neutral fraction of the IGM. We furthermore find that this change in galactic properties leads to systematically different Ly<jats:italic>α</jats:italic> spectra which can be used to differentiate the two competing effects. Using the CANDELSz7 survey measurements which indicate slightly broader lines at <jats:italic>z</jats:italic> ∼ 6, we find that the scenario of a mere increase in the galactic column density toward higher <jats:italic>z</jats:italic> is highly unlikely. We also show that a decrease in outflow velocity is not ruled out by existing data but leads to more prominent blue peaks at <jats:italic>z</jats:italic> &gt; 6. Our results caution using Ly<jats:italic>α</jats:italic> observations to estimate the IGM neutral fraction without accounting for the potential change in the galactic properties, e.g., by mapping out the evolution of Ly<jats:italic>α</jats:italic> spectral characteristics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Since the discovery of chemically peculiar stars in globular clusters in the last century, the study of multiple populations has become increasingly important, given that chemical inhomogeneity is found in almost all globular clusters. Despite various proposed theories attempting to explain this phenomenon, fitting all the observational evidence in globular clusters with one single theory remains notoriously difficult and currently unsuccessful. In order to improve existing models and motivate new ones, we are observing globular clusters at critical conditions, e.g., metal-rich end, metal-poor end, and low mass end. In this paper, we present our first attempt to investigate multiple populations in low mass globular clusters. We obtained low-resolution spectra around 4000 Å of 30 members of the globular cluster Palomar 13 using OSIRIS/Multi-object spectrograph mounted at the Gran Telescopio Canarias. The membership of red giant branch stars is confirmed by the latest proper motions from Gaia DR2 and literature velocities. After comparing the measured CN and CH spectral indices with those of the stellar models, we found a clear sign of nitrogen variation among the red giant branch stars. Palomar 13 may be the lowest mass globular cluster showing multiple populations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There is an ongoing debate on whether feedback from active galactic nuclei (AGNs) can effectively regulate the star formation activities in their host galaxies. To investigate the feedback effect of AGN-driven outflows, we perform integral-field spectroscopic observations of 40 moderate-luminosity (<jats:inline-formula> <jats:tex-math> <?CDATA ${10}^{41.5}\lt {L}_{[O}\,{\rm\small{III}}];\mathrm{cor}\lt {10}^{43.1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd5acieqn1.gif" xlink:type="simple" /> </jats:inline-formula> erg s<jats:sup>−1</jats:sup> ) Type-2 AGNs at <jats:italic>z</jats:italic> &lt; 0.1, which present strong outflow signatures in the integrated [O <jats:sc>iii</jats:sc>] kinematics. Based on the radial profile of the normalized [O <jats:sc>iii</jats:sc>] velocity dispersion by stellar velocity dispersion, we measure the kinematic outflow size and extend the kinematic outflow size–luminosity relation reported in Kang &amp; Woo into a wider luminosity range (over four orders of magnitude in [O <jats:sc>iii</jats:sc>] luminosity). The shallow slope of the kinematic outflow size–luminosity relation indicates that while ionizing photons can reach out further, kinetic energy transfer is much less efficient due to various effects, demonstrating the importance of kinematical analysis in quantifying the outflow size and energetics. By comparing the outflow kinematics with the host galaxy properties, we find that AGNs with strong outflows have higher star formation rate and higher H <jats:sc>i</jats:sc> gas fraction than those AGNs with weak outflows. These results suggest that the current feedback from AGN-driven outflows do not instantaneously suppress or quench the star formation in the host galaxies while its effect is delayed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use the wealth of deep archival optical spectroscopy on the GOODS-South field from Keck, the VLT, and other facilities to select candidate high-redshift Lyman continuum (LyC) leakers in the Hubble Deep UV Legacy Survey (HDUV) data set. We select sources at <jats:inline-formula> <jats:tex-math> <?CDATA $2.35\lt z\lt 3.05$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd5b8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where the HST/WFC3 F275W filter probes only the redshifted LyC. We find five moderately F275W-bright sources (four detected at <jats:inline-formula> <jats:tex-math> <?CDATA $\gtrsim 3\sigma $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd5b8ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> significance) in this redshift range. However, two of these show evidence in their optical spectra of contamination by foreground galaxies along the line of sight. We then perform an F275W error-weighted sum of the fluxes of all 129 galaxies at <jats:inline-formula> <jats:tex-math> <?CDATA $2.35\lt z\lt 3.05$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd5b8ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> in both the GOODS-N and GOODS-S HDUV areas to estimate the total ionizing flux. The result is dominated by just five candidate F275W-bright LyC sources. Lastly, we examine the contributions to the metagalactic ionizing background, finding that, at the sensitivity of the HDUV F275W data and allowing for the effects of LyC transmission in the intergalactic medium (IGM), star-forming galaxies can match the UV flux required to maintain an ionized IGM at <jats:inline-formula> <jats:tex-math> <?CDATA $z\sim 2.5$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd5b8ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The advent of Gaia, capable of measuring stellar wobbles caused by orbiting planets, raised interest in the astrometric detection of exoplanets. Another source of such wobbles (often also called jitter) is stellar magnetic activity. A quantitative assessment of the stellar astrometric jitter is important for a more reliable astrometric detection and characterization of exoplanets. We calculate the displacement of the solar photocenter due to the magnetic activity for an almost 16 yr period (1999 February 2–2014 August 1). We also investigate how the displacement depends on the spectral passband chosen for observations, including the wavelength range to be covered by the upcoming Small-JASMINE mission of JAXA. This is done by extending the SATIRE-S model for solar irradiance variability to calculating the displacement of the solar photocenter caused by the magnetic features on the surface of the Sun. We found that the peak-to-peak amplitude of the solar photocenter displacement would reach 0.5 <jats:italic>μ</jats:italic>as if the Sun were located 10 pc away from the observer and observed in the Gaia G filter. This is by far too small to be detected by the Gaia mission. However, the Sun is a relatively inactive star so one can expect significantly larger signals for younger, and, consequently, more active stars. The model developed in this study can be combined with the simulations of emergence and surface transport of magnetic flux which have recently become available to model the astrometric jitter over the broad range of magnetic activities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This study presents the mass segregation of 35 Galactic globular clusters (GCs) through the radial profile of the mean mass of main-sequence stars. Most of them are found to be mass segregated due to two-body relaxation effects. The GCs with a larger core to half-mass–radius ratio tend to be less mass segregated. Recent simulations show that energy sources can quench mass segregation in relaxed GCs. Combining mass segregation and core binary fractions (<jats:italic>f</jats:italic> <jats:sub> <jats:italic>c</jats:italic> </jats:sub>), we find a moderate anticorrelation between them when <jats:italic>f</jats:italic> <jats:sub> <jats:italic>c</jats:italic> </jats:sub> is below 0.15. Four GCs that have a small amount of mass segregation are selected as possible intermediate-mass black hole holders. However, none of them are strong candidates considering their half-mass relaxation times.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent detection of sub-TeV emission from gamma-ray bursts (GRBs) represents a breakthrough in the GRB study. The multiwavelength data of the afterglows of GRB 190114C support the synchrotron self-Compton (SSC) origin for its sub-TeV emission. We present a comparative analysis on the SSC emission of GRB afterglows in the homogeneous and wind environments in the framework of the forward shock model. The <jats:italic>γ</jats:italic> <jats:italic>γ</jats:italic> absorption of very-high-energy photons due to pair production within the source and the Klein–Nishina effect on the inverse Compton scattering are considered. Generally a higher SSC flux is expected for a larger circum-burst density due to a larger Compton parameter, but meanwhile the internal <jats:italic>γ</jats:italic> <jats:italic>γ</jats:italic> absorption is more severe for sub-TeV emission. The flux ratio between the SSC component and the synchrotron component decreases more quickly with time in the wind medium case than in the homogeneous density medium case. The light curves of the SSC emission are also different for the two types of media. We also calculate the cascade emission resulting from the absorbed high-energy photons. In the ISM environment with <jats:italic>n</jats:italic> ≳ 1 cm<jats:sup>−3</jats:sup>, the cascade synchrotron emission could be comparable to the synchrotron emission of the primary electrons in the optical band, which may flatten the optical afterglow light curve at an early time (<jats:italic>t</jats:italic> &lt; 1 hr). In the wind medium with <jats:italic>A</jats:italic> <jats:sub>*</jats:sub> ≳ 0.1, the cascade emission in the eV–GeV band is comparable or even larger than the emission of the primary electrons at the early time.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We carry out a comparative analysis of the metallicities from the stellar, neutral-gas, and ionized-gas components in the metal-rich spiral galaxy M83. We analyze spectroscopic observations taken with the Hubble Space Telescope, the Large Binocular Telescope, and the Very Large Telescope. We detect a clear depletion of the H <jats:sc>i</jats:sc> gas, as observed from the H <jats:sc>i</jats:sc> column densities in the nuclear region of this spiral galaxy. We find column densities of log[<jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) cm<jats:sup>−2</jats:sup>] &lt; 20.0 at galactocentric distances of &lt;0.18 kpc, in contrast to column densities of log[<jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) cm<jats:sup>−2</jats:sup>] ∼ 21.0 in the galactic disk, a trend observed in other nearby spiral galaxies. We measure a metallicity gradient of −0.03 ± 0.01 dex kpc<jats:sup>−1</jats:sup> for the ionized gas, comparable to the metallicity gradient of a local benchmark of 49 nearby star-forming galaxies of −0.026 ± 0.002 dex kpc<jats:sup>−1</jats:sup>. Our cospatial metallicity comparison of the multiphase gas and stellar populations shows excellent agreement outside of the nucleus of the galaxy, hinting at a scenario where the mixing of newly synthesized metals from the most massive stars in the star clusters takes longer than their lifetimes (∼10 Myr). Finally, our work shows that caution must be taken when studying the metallicity gradient of the neutral-gas component in star-forming galaxies, since this can be strongly biased, as these environments can be dominated by molecular gas. In these regions the typical metallicity tracers can provide inaccurate abundances, as they may trace both the neutral- and molecular-gas components.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The lunar wake is usually rapidly refilled when the background plasma is substantially subsonic. Here we present observational case studies, by the two ARTEMIS spacecraft, of the lunar wakes in the magnetosheath near the magnetopause under transonic plasma flows with relatively large plasma beta and different magnetic field orientations. The associated background plasma betas are near 1, suggesting that the plasmas are not strongly controlled by the magnetic fields. As a result, the part of the lunar wake under subsonic plasma was rapidly refilled. Pitch angle distributions reveal that a significant portion of the refilling ions are from the downstream wake. This is consistent with the fact that higher sound speed than bulk speed of the background plasma enables downstream particles to get access to upstream wake due to the pressure gradient. The other part under supersonic plasma remains a typical wake structure with high plasma density or flux depletions. Our results show that the Mach number and plasma beta primarily determine the rapid refilling of the lunar wake, which is allowed only in subsonic plasma with plasma beta greater than or close to 1 and hardly influenced at all by the magnetic field orientation.</jats:p>