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<jats:title>Abstract</jats:title> <jats:p>We present new empirical constraints on the evolution of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rho }_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec81ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, the cosmological mass density of molecular hydrogen, back to <jats:italic>z</jats:italic> ≈ 2.5. We employ a statistical approach measuring the average observed 850 <jats:italic>μ</jats:italic>m flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to a span where the 850 <jats:italic>μ</jats:italic>m band probes the Rayleigh–Jeans tail of thermal dust emission in the rest frame, and can therefore be used as an estimate of the mass of the interstellar medium. Our sample comprises of ≈150,000 galaxies in the UK InfraRed Telescope Infrared Deep Sky Survey Ultra-Deep Survey field with near-infrared magnitudes <jats:italic>K</jats:italic> <jats:sub>AB</jats:sub> ≤ 25 mag and photometric redshifts with corresponding probability distribution functions derived from deep 12-band photometry. With a sample approximately 2 orders of magnitude larger than in previous works we significantly reduce statistical uncertainties on <jats:inline-formula> <jats:tex-math> <?CDATA ${\rho }_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec81ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:italic>z</jats:italic> ≈ 2.5. Our measurements are in broad agreement with recent direct estimates from blank field molecular gas surveys, finding that the epoch of molecular gas coincides with the peak epoch of star formation with <jats:inline-formula> <jats:tex-math> <?CDATA ${\rho }_{{{\rm{H}}}_{2}}\approx 2\times {10}^{7}\,{M}_{\odot }\,{\mathrm{Mpc}}^{-3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec81ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> at <jats:italic>z</jats:italic> ≈ 2. We demonstrate that <jats:inline-formula> <jats:tex-math> <?CDATA ${\rho }_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec81ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> can be broadly modeled by inverting the star formation rate (SFR) density with a fixed or weakly evolving star formation efficiency. This “constant efficiency” model shows a similar evolution to our statistically derived <jats:inline-formula> <jats:tex-math> <?CDATA ${\rho }_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec81ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, indicating that the dominant factor driving the peak star formation history at <jats:italic>z</jats:italic> ≈ 2 is a larger supply of molecular gas in galaxies rather than a significant evolution of the SFR efficiency within individual galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the efficiency of grain alignment by radiative torques (RATs) for an ensemble of irregular grains. The grains are modeled as ensembles of oblate and prolate spheroids, deformed as Gaussian random ellipsoids, and their scattering interactions are solved using numerically exact methods. We define the fraction of the grains that both rotate fast and demonstrate perfect alignment with grain long axes perpendicular to the magnetic field. We quantify a factor related to the efficacy of alignment and show that it is related to a <jats:inline-formula> <jats:tex-math> <?CDATA ${q}_{\max }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf096ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> factor of the analytical model of the RAT theory. For the interstellar radiation field, our results indicate that the degree of RAT alignment can reach ∼0.5, which may be sufficient to explain observations even if grains do not have magnetic inclusions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We compare maps of scattering polarization signals obtained from three-dimensional (3D) radiation transfer calculations in a magnetoconvection model of the solar atmosphere using formal solvers based on the “short characteristics” (SC) and the “long characteristics” (LC) methods. The SC method requires less computational work, but it is known to introduce spatial blurring in the emergent radiation for inclined lines of sight. For polarized radiation this effect is generally more severe due to it being a signed quantity and to the sensitivity of the scattering polarization to the model’s inhomogeneities. We study the differences in the polarization signals of the emergent spectral line radiation calculated with such formal solvers. We take as a case study already published results of the scattering polarization in the Sr <jats:sc>i</jats:sc> 4607 Å line obtained with the SC method, demonstrating that in high-resolution grids it is accurate enough for that type of study. In general, the LC method is the preferred one for accurate calculations of the emergent radiation, which is the reason why it is now one of the options in the public version of the 3D radiative transfer code PORTA.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Streamers and pseudostreamers structure the corona at the largest scales, as seen in both eclipse and coronagraph white-light images. Their inverted-goblet appearance encloses broad coronal loops at the Sun and tapers to a narrow radial stalk away from the star. The streamer associated with the global solar dipole magnetic field is long-lived, predominantly contains a single arcade of nested loops within it, and separates opposite-polarity interplanetary magnetic fields with the heliospheric current sheet (HCS) anchored at its apex. Pseudostreamers, on the other hand, are transient, enclose double arcades of nested loops, and separate like-polarity fields with a dense plasma sheet. We use numerical magnetohydrodynamic simulations to calculate, for the first time, the formation of pseudostreamers in response to photospheric magnetic-field evolution. Convective transport of a minority-polarity flux concentration, initially positioned under one side of a streamer, through the streamer boundary into the adjacent preexisting coronal hole forms the pseudostreamer. Interchange magnetic reconnection at the overlying coronal null point(s) governs the development of the pseudostreamer above—and of a new satellite coronal hole behind—the moving minority polarity. The reconnection dynamics liberate coronal-loop plasma that can escape into the heliosphere along so-called separatrix-web (“S-Web”) arcs, which reach far from the HCS and the solar equatorial plane, and can explain the origin of high-latitude slow solar wind. We describe the implications of our results for in situ and remote-sensing observations of the corona and heliosphere as obtained, most recently, by Parker Solar Probe and Solar Orbiter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The presence of planets or substellar objects still embedded in their native protoplanetary disks is indirectly suggested by disk substructures like gaps, cavities, and spirals. However, these companions are rarely detected. We present Very Large Telescope/NACO high-contrast images in the <jats:italic>J</jats:italic>, <jats:italic>H</jats:italic>, <jats:italic>K</jats:italic> <jats:sub> <jats:italic>S</jats:italic> </jats:sub>, and <jats:inline-formula> <jats:tex-math> <?CDATA $L^{\prime} $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec42ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> bands of the young star [BHB2007]-1 probing the inclined disk in scattered light and revealing the probable presence of a companion. The point source is detected in the <jats:inline-formula> <jats:tex-math> <?CDATA $L^{\prime} $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec42ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> band in spatial correspondence with complementary Very Large Array observations. This object is constrained to have a mass in the range of 37–47 <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> and is located at 50 au from the central star, inside the 70 au-large disk cavity recently imaged by the Atacama Large Millimeter/submillimeter Array (ALMA), that is absent from our NACO data (down to 20 au). This mass range is compatible with the upper end derived from the size of the ALMA cavity. The NIR disk brightness is highly asymmetric around the minor axis, with the southern side 5.5 times brighter than the northern side. The constant amount of asymmetry across all wavelengths suggests that it is due to a shadow cast by a misaligned inner disk. The massive companion that we detect could, in principle, explain the possible disk misalignment, as well as the different cavity sizes inferred by the NACO and ALMA observations. The confirmation and characterization of the companion is entrusted to future observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The polar magnetic field precursor is considered to be the most robust and physics-based method for the prediction of the next solar cycle strength. However, to make a reliable prediction of a cycle, is the polar field at the solar minimum of the previous cycle enough or do we need the polar field of many previous cycles? To answer this question, we performed several simulations using Babcock–Leighton-type flux-transport dynamo models with a stochastically forced source for the poloidal field (<jats:italic>α</jats:italic> term). We show that when the dynamo is operating near the critical dynamo transition or only weakly supercritical, the polar field of cycle <jats:italic>n</jats:italic> determines the amplitude of the next several cycles (at least three). However, when the dynamo is substantially supercritical, this correlation of the polar field is reduced to one cycle. This change in the memory of the polar field from multiple to one cycle with the increase of the supercriticality of the dynamo is independent of the importance of various turbulent transport processes in the model. Our this conclusion contradicts the existing idea. We further show that when the dynamo operates near the critical transition, it produces frequent extended episodes of weaker activity, resembling the solar grand minima. The occurrence of grand minima is accompanied by the multicycle correlation of the polar field. The frequency of grand minima decreases with the increase of supercriticality of the dynamo.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two magnetic braking models are implemented in <jats:monospace>MESA</jats:monospace> for use in the <jats:monospace>MIST</jats:monospace> stellar model grids. Stars less than about 1.3 solar masses are observed to spin down over time through interaction with their magnetized stellar winds (i.e., magnetic braking). This is the basis for gyrochronology and is fundamental to the evolution of lower-mass stars. The detailed physics behind magnetic braking are uncertain, as are 1D stellar evolution models. Thus, we calibrate our models and compare to data from open clusters. Each braking model tested here is capable of reproducing aspects of the data, with important distinctions; neither fully accounts for the observations. The Matt et al. prescription matches the slowly rotating stars observed in open clusters but tends to overestimate the presence of rapidly rotating stars. The Garraffo et al. prescription often produces too much angular momentum loss to accurately match the observed slow sequence for lower-mass stars but reproduces the bimodal nature of slowly and rapidly rotating stars observed in open clusters fairly well. Our models additionally do not reproduce the observed solar lithium depletion, corroborating previous findings that effects other than rotation may be important. We find additional evidence that some level of mass dependency may be missing in these braking models to match the rotation periods observed in clusters older than 1 Gyr better.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the decay phase of solar energetic particle (SEP) events, particle intensities observed by widely separated spacecraft usually present comparable intensities (within a factor of 2–3) that evolve similarly in time. The phenomenon of SEP events is called a reservoir, which could be observed frequently in intensive gradual SEP events. In this work, we find the effects of the magnetic boundary could help to form the reservoir phenomenon in energetic proton and electron events. In the 1978 January 1 and the 2000 November 8 SEP events, we find the effects of the magnetic boundary associated with the reservoir phenomenon were observed simultaneously in the sheath of magnetic cloud/interplanetary coronal mass ejection. Based on the observations, we suggest that the effects of the magnetic boundary could be due to the magnetic mirrors and/or the small diffusion coefficients in the sheath region and they could help to form the reservoir phenomenon in both the energetic proton and electron events in some large SEP events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present <jats:sup>12</jats:sup>CO (<jats:italic>J</jats:italic> = 2–1), <jats:sup>13</jats:sup>CO (<jats:italic>J</jats:italic> = 2–1), and C<jats:sup>18</jats:sup>O (<jats:italic>J</jats:italic> = 2–1) observations toward GMC-8, one of the most massive giant molecular clouds (GMCs) in M33 using ALMA with an angular resolution of 0.″44 × 0.″27 (∼2 pc × 1 pc). The earlier studies revealed that its high-mass star formation is inactive in spite of a sufficient molecular reservoir with a total mass of ∼10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The high-angular resolution data enable us to resolve this peculiar source down to a molecular clump scale. One of the GMC’s remarkable features is that a round-shaped gas structure (the “Main cloud”) extends over the ∼50 pc scale, which is quite different from the other two active star-forming GMCs dominated by remarkable filaments/shells obtained by our series of studies in M33. The fraction of the relatively dense gas traced by the <jats:sup>13</jats:sup>CO data with respect to the total molecular mass is only ∼2%, suggesting that their spatial structure and the density are not well developed to reach an active star formation. The CO velocity analysis shows that the GMC is composed of a single component as a whole, but we found some local velocity fluctuations in the Main cloud and extra blueshifted components at the outer regions. Comparing the CO with previously published large-scale H <jats:sc>i</jats:sc> data, we suggest that an external atomic gas flow supplied a sufficient amount of material to grow the GMC up to ∼10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present radio observation of a millisecond pulsar PSR J0621+1002 using the Five-hundred-meter Aperture Spherical radio Telescope. The pulsar shows periodic pulse intensity modulations for both the first and the third pulse components. The fluctuation spectrum of the first pulse component has one peak of 3.0 ± 0.1 pulse periods, while that of the third pulse component has two diffused peaks of 3.0 ± 0.1 and 200 ± 1 pulse periods. The single pulse timing analysis is carried out for this pulsar and the single pulses can be divided into two classes based on the post-fit timing residuals. We examined the achievable timing precision using only the pulses in one class or bright pulses. However, the timing precision improvement is not achievable.</jats:p>