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<jats:title>Abstract</jats:title> <jats:p>We present a high-resolution study of the cold molecular gas as traced by CO(1-0) in the unlensed <jats:italic>z</jats:italic> ∼ 3.4 submillimeter galaxy SMM J13120+4242, using multiconfiguration observations with the Karl G. Jansky Very Large Array (JVLA). The gas reservoir, imaged on 0.″39 (∼3 kpc) scales, is resolved into two components separated by ∼11 kpc with a total extent of 16 ± 3 kpc. Despite the large spatial extent of the reservoir, the observations show a CO(1-0) FWHM linewidth of only 267 ± 64 km s<jats:sup>−1</jats:sup>. We derive a revised line luminosity of <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\mathrm{CO}(1-0)}^{{\prime} }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>CO</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6105ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> = (10 ± 3) × 10<jats:sup>10</jats:sup> K km s<jats:sup>−1</jats:sup> pc<jats:sup>2</jats:sup> and a molecular gas mass of <jats:italic>M</jats:italic> <jats:sub>gas</jats:sub> = (13 ± 3)× 10<jats:sup>10</jats:sup> (<jats:italic>α</jats:italic> <jats:sub>CO</jats:sub>/1) <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Despite the presence of a velocity gradient (consistent with previous resolved CO(6-5) imaging), the CO(1-0) imaging shows evidence for significant turbulent motions that are preventing the gas from fully settling into a disk. The system likely represents a merger in an advanced stage. Although the dynamical mass is highly uncertain, we use it to place an upper limit on the CO-to-H<jats:sub>2</jats:sub> mass conversion factor <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> of 1.4. We revisit the SED fitting, finding that this galaxy lies on the very massive end of the main sequence at <jats:italic>z</jats:italic> = 3.4. Based on the low gas fraction, short gas depletion time, and evidence for a central AGN, we propose that SMM J13120 is in a rapid transitional phase between a merger-driven starburst and an unobscured quasar. The case of SMM J13120 highlights how mergers may drive important physical changes in galaxies without pushing them off the main sequence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Astrophysical jets are ubiquitous in the universe and often associated with compact objects, and their interactions with the ambient medium not only dissipate their own energy but also provide ideal circumstances for particle acceleration. By means of theoretical analysis and particle-in-cell simulations, here we study the ion acoustic shock wave (IASW) formation and consequent ion acceleration when electron–positron (<jats:italic>e</jats:italic> <jats:sup>−</jats:sup> <jats:italic>e</jats:italic> <jats:sup>+</jats:sup>) jets are injected into ambient electron–ion plasmas. It is found that the Buneman instability can be excited first, which induces the formation of an ion acoustic wave (IAW). As the amplitude of the IAW increases, its waveform is steepened and subsequently an IASW is formed. Some ions in the ambient plasmas will be reflected when they encounter the IASW, and thus can be accelerated to form an energetic ion beam. For an initial <jats:italic>e</jats:italic> <jats:sup>−</jats:sup> <jats:italic>e</jats:italic> <jats:sup>+</jats:sup> jet with the Lorentz factor <jats:italic>γ</jats:italic> <jats:sub>0</jats:sub> = 100 and the ion–electron mass ratio <jats:italic>m</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub>/<jats:italic>m</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> = 1836, the ions can be accelerated up to 580 MeV. This study deepens our understanding of the fireball model of gamma-ray bursts, the shock model of pulsar wind nebulae, the origin of cosmic rays, and other related astrophysical processes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Accurate stellar ages are essential for our understanding of the star formation history of the Milky Way and Galactic chemical evolution, as well as to constrain exoplanet formation models. Gyrochronology, a relationship between stellar rotation and age, appears to offer a reliable age indicator for main-sequence (MS) stars over the mass range of approximately 0.6–1.3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Those stars lose their angular momentum due to magnetic braking and as a result their rotation speeds decrease with age. Although current gyrochronology relations have been fairly well tested for young MS stars with masses greater than 1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, primarily in young open clusters, insufficient tests exist for older and lower mass MS stars. Binary stars offer the potential to expand and fill in the range of ages and metallicity over which gyrochronology can be empirically tested. In this paper, we demonstrate a Monte Carlo approach to evaluate gyrochronology models using binary stars. As examples, we used five previously published wide binary pairs. We also demonstrate a Monte Carlo approach to assess the precision and accuracy of ages derived from each gyrochronology model. For the traditional Skumanich models, the age uncertainties are <jats:italic>σ</jats:italic> <jats:sub>age</jats:sub>/age = 15%–20% for stars with <jats:italic>B</jats:italic> − <jats:italic>V</jats:italic> = 0.65 and <jats:italic>σ</jats:italic> <jats:sub>age</jats:sub>/age = 5%–10% for stars with <jats:italic>B</jats:italic> − <jats:italic>V</jats:italic> = 1.5 and rotation period <jats:italic>P</jats:italic> ≤ 20 days.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We revisit the role of longitudinal waves in driving the solar wind. We study how the <jats:italic>p</jats:italic>-mode-like vertical oscillation on the photosphere affects the properties of solar winds in the framework of Alfvén-wave-driven winds. We perform a series of one-dimensional magnetohydrodynamical numerical simulations from the photosphere to beyond several tens of solar radii. We find that the mass-loss rate drastically increases with the longitudinal-wave amplitude at the photosphere by up to a factor of ∼4, in contrast to the classical understanding that acoustic waves hardly affect the energetics of the solar wind. The addition of the longitudinal fluctuation induces longitudinal-to-transverse wave mode conversion in the chromosphere, which results in enhanced Alfvénic Poynting flux in the corona. Consequently, coronal heating is promoted to give higher coronal density by chromospheric evaporation, leading to the increased mass-loss rate. This study clearly shows the importance of longitudinal oscillation in the photosphere and mode conversion in the chromosphere in determining the basic properties of the wind from solar-like stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Strong high-ionization lines such as He <jats:sc>ii</jats:sc> of young galaxies are puzzling at high and low redshift. Although recent studies suggest the existence of nonthermal sources, whether their ionizing spectra can consistently explain multiple major emission lines remains a question. Here we derive the general shapes of the ionizing spectra for three local extremely metal-poor galaxies (EMPGs) that show strong He <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>4686. We parameterize the ionizing spectra composed of a blackbody and power-law radiation mimicking various stellar and nonthermal sources. We use photoionization models for nebulae and determine seven parameters of the ionizing spectra and nebulae by Markov Chain Monte Carlo methods, carefully avoiding systematics of abundance ratios. We obtain the general shapes of ionizing spectra explaining ∼10 major emission lines within observational errors with smooth connections from observed X-ray and optical continua. We find that an ionizing spectrum of one EMPG has a blackbody-dominated shape, while the others have convex downward shapes at &gt;13.6 eV, which indicate a diversity of the ionizing spectrum shapes. We confirm that the convex downward shapes are fundamentally different from ordinary stellar spectrum shapes, and that the spectrum shapes of these galaxies are generally explained by the combination of the stellar and ultraluminous X-ray sources. Comparisons with stellar synthesis models suggest that the diversity of the spectrum shapes arises from differences in the stellar age. If galaxies at <jats:italic>z</jats:italic> ≳ 6 are similar to the EMPGs, high-energy (&gt;54.4 eV) photons of the nonstellar sources negligibly contribute to cosmic reionization due to relatively weak radiation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Utilizing the data and tools provided through the NASA Ames PAH IR Spectroscopic Database (PAHdb), we study the PAH component of over 900 Spitzer-IRS galaxy spectra. Employing a database-fitting approach, the average PAH size, the PAH size distribution, and PAH ionization fraction are deduced. In turn, we examine their connection with the properties of the host galaxy. We found that PAH population within galaxies consists of middle-sized PAHs with an average number of carbon atoms of <jats:inline-formula> <jats:tex-math> <?CDATA $\overline{{N}_{C}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac666fieqn1.gif" xlink:type="simple" /> </jats:inline-formula> = 55, and a charge state distribution of ∼40% ionized—60% neutral. We describe a correlation between the 6.2/11.2 <jats:italic>μ</jats:italic>m PAH ratio with the ionization parameter (<jats:inline-formula> <jats:tex-math> <?CDATA $\gamma \equiv {({G}_{0}/{n}_{{\rm{e}}})({T}_{\mathrm{gas}}/1\ {\rm{K}})}^{0.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>γ</mml:mi> <mml:mo>≡</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>G</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>gas</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>1</mml:mn> <mml:mspace width="0.33em" /> <mml:mi mathvariant="normal">K</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac666fieqn2.gif" xlink:type="simple" /> </jats:inline-formula>), a moderate correlation between the 8.6/11.2 <jats:italic>μ</jats:italic>m PAH ratio and specific star formation rate, and a weak anticorrelation between <jats:italic>γ</jats:italic> and <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>. From the PAHdb decomposition, we provide estimates for the 3.3 <jats:italic>μ</jats:italic>m PAH band, not covered by Spitzer observations, and establish a correlation between the 3.3/11.2 <jats:italic>μ</jats:italic>m PAH ratio with <jats:italic>N</jats:italic> <jats:sub>C</jats:sub>. We further deliver a library of mid-IR PAH template spectra parameterized on PAH size and ionization fraction, which can be used in galaxy spectral energy distribution fitting codes for the modeling of the mid-IR PAH emission component in galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ∼20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm<jats:sup>−3</jats:sup>, and rotation measure (RM) of +456 rad m<jats:sup>−2</jats:sup> using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523−7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ∼1 mJy at 1400 MHz and ∼25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index <jats:italic>α</jats:italic> ≈ −3, where <jats:italic>S</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub> ∝ <jats:italic>ν</jats:italic> <jats:sup> <jats:italic>α</jats:italic> </jats:sup>) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The spectra of active galactic nuclei exhibit broad-emission lines that presumably originate in the broad-line region (BLR) with gaseous-dusty clouds in a predominantly Keplerian motion around the central black hole. Signatures of both inflow and outflow motion are frequently seen. The dynamical character of BLR is consistent with the scenario that has been branded as the failed radiatively accelerated dusty outflow. In this scheme, frequent high-velocity impacts of BLR clouds falling back onto the underlying accretion disk are predicted. The impact velocities depend mainly on the black hole mass, accretion rate, and metallicity, and they range from a few km s<jats:sup>−1</jats:sup> up to thousands of km s<jats:sup>−1</jats:sup>. Formation of strong shocks due to the collisions can give rise to the production of relativistic particles and associated radiation signatures. In this work, the nonthermal radiation generated in this process is investigated, and the spectral energy distributions for different parameter sets are presented. We find that the nonthermal processes caused by the impacts of clouds can lead to emission in the X-ray and the gamma-ray bands, playing the cloud density and metallicity key roles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical spectroscopy observations of 145 high-mass pre-main-sequence candidates from the catalog of Vioque et al. 2020 From these, we provide evidence for the Herbig nature of 128 sources. This increases the number of known objects of the class by ∼50%. We determine the stellar parameters of these sources using the spectra and Gaia EDR3 data. The new sources are well distributed in mass and age, with 23 sources between 4 and 8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and 32 sources above 8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Accretion rates are inferred from H<jats:italic>α</jats:italic> and H<jats:italic>β</jats:italic> luminosities for 104 of the new Herbigs. These accretion rates, combined with previous similar estimates, allow us to analyze the accretion properties of Herbig stars using the largest sample ever considered. We provide further support to the existence of a break in accretion properties at ∼3–4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which was already reported for the previously known Herbig stars. We re-estimate the potential break in accretion properties to be at <jats:inline-formula> <jats:tex-math> <?CDATA ${3.87}_{-0.96}^{+0.38}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>3.87</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.96</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.38</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5c46ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. As observed for the previously known Herbig stars, the sample of new Herbig stars independently suggests intense inner-disk photoevaporation for sources with masses above ∼7 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. These observations provide robust observational support to the accuracy of the Vioque et al. 2020 catalog of Herbig candidates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal active regions are studied using Hinode/EIS observations in the EUV line Fe <jats:sc>xii</jats:sc> <jats:italic>λ</jats:italic>195.12 by analyzing their line profiles from 2006 December to 2019 December. The period covers the last 2 yr of solar cycle 23 and solar cycle 24 fully. Active regions are the main source of magnetic field in the solar atmosphere, important in its heating and dynamics. Line profiles were obtained from various active regions spread across the Sun on a monthly basis from which we obtained the intensity, line width, Doppler velocity, and centroid and examined their variation during the solar cycle. The histograms of the Doppler velocity and centroid show that they behave in six different ways with respect to the position of rest wavelength. In addition, the shifts in the centroid were found to be more compared to the Doppler velocity. The variation of the line width with respect to the Doppler velocity or the centroid mostly follows a second-degree polynomial. A multicomponent line profile is simulated to explain the difference in the behavior of the Doppler velocity and the centroid with respect to the line width. We also find that the intensity and the line width of the different data sets show a global dependence on the solar cycle with a good correlation. The implications of the results for the coronal heating and dynamics are pointed out.</jats:p>