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<jats:title>Abstract</jats:title> <jats:p>The decay index of solar magnetic fields is known as an important parameter in regulating solar eruptions from the standpoint of the torus instability. In particular, a saddle-like profile of decay index, which hosts a local torus-stable regime at higher altitudes than where the decay index first exceeds the instability threshold, is found to be associated with some confined or two-step eruptions. To understand the occurrence of such a profile, we employed dipoles to emulate different kinds of photospheric flux distributions. Corroborated by observations of representative active regions, our major results are as follows: (1) in bipolar configurations the critical height increases away from the AR center along the polarity inversion line (PIL) and its average is roughly half of the centroid distance between opposite polarities; (2) in quadrupolar configurations saddle-like profiles appear above the PIL when the two dipoles oriented in the same direction are significantly more separated in this direction than in the perpendicular direction, and when the two dipoles are oriented differently or have unequal fluxes; and (3) saddle-like profiles in quadrupolar configurations are associated with magnetic skeletons such as a null point or a hyperbolic flux tube, and the role of such profiles in eruptions is anticipated to be double-edged if magnetic reconnection is involved.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use Paschen-<jats:italic>β</jats:italic> (Pa<jats:italic>β</jats:italic>; 1282 nm) observations from the Hubble Space Telescope G141 grism to study the star formation and dust-attenuation properties of a sample of 29 low-redshift (<jats:italic>z</jats:italic> &lt; 0.287) galaxies in the CANDELS Ly<jats:italic>α</jats:italic> Emission at Reionization survey. We first compare the nebular attenuation from Pa<jats:italic>β</jats:italic>/H<jats:italic>α</jats:italic> with the stellar attenuation inferred from the spectral energy distribution, finding that the galaxies in our sample are consistent with an average ratio of the continuum attenuation to the nebular gas of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. Much of this scatter is linked to a large variation between the nebular dust attenuation as measured by (space-based) Pa<jats:italic>β</jats:italic> to (ground-based) H<jats:italic>α</jats:italic> to that from (ground-based) H<jats:italic>α</jats:italic>/H<jats:italic>β</jats:italic>. This implies there are important differences between attenuation measured from grism-based/wide-aperture Pa<jats:italic>β</jats:italic> fluxes and the ground-based/slit-measured Balmer decrement. We next compare star formation rates (SFRs) from Pa<jats:italic>β</jats:italic> to those from dust-corrected UV. We perform a survival analysis to infer a census of Pa<jats:italic>β</jats:italic> emission implied by both detections and nondetections. We find evidence that galaxies with lower stellar mass have more scatter in their ratio of Pa<jats:italic>β</jats:italic> to attenuation-corrected UV SFRs. When considering our Pa<jats:italic>β</jats:italic> detection limits, this observation supports the idea that lower-mass galaxies experience “burstier” star formation histories. Together, these results show that Pa<jats:italic>β</jats:italic> is a valuable tracer of a galaxy’s SFR, probing different timescales of star formation and potentially revealing star formation that is otherwise missed by UV and optical tracers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the present work, we study the energization and displacement of heavy ions through the use of test particles interacting with the electromagnetic fields of magnetohydrodynamic (MHD) turbulence. These fields are obtained from pseudospectral direct numerical solutions of the compressible three-dimensional MHD equations with a strong background magnetic field. We find particle energization to be predominantly perpendicular as the ions become heavier (lower charge-to-mass ratio) and that high displacement is detrimental for perpendicular energization. On the other hand, perpendicular displacement is unaffected by the charge-to-mass ratio, which we explain with a simple guide center model. Using Voronoi tessellation along with this model, we analyze preferential concentration and find that particles behave as tracers in the perpendicular plane, clustering in regions with ∇<jats:sub>⊥</jats:sub> · <jats:bold> <jats:italic>u</jats:italic> </jats:bold> <jats:sub>⊥</jats:sub> &lt; 0. These regions also have (∇ × <jats:bold> <jats:italic>E</jats:italic> </jats:bold>)<jats:sub> <jats:italic>z</jats:italic> </jats:sub> &lt; 0, which is optimal for perpendicular energization, thus providing a mechanism to understand precedent results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The gravitational coupling between large-scale perturbations and small-scale perturbations leads to anisotropic distortions of the small-scale matter distribution. The measured local small-scale power spectrum can thus be used to infer the large-scale matter distribution. In this paper, we present a new tidal reconstruction algorithm for reconstructing large-scale modes using the full three-dimensional tidal shear information. We apply it to simulated dark matter halo fields and find the reconstructed large-scale density field correlates well with the original matter density field on large scales, improving upon the previous tidal reconstruction method, which only uses two transverse shear fields. This has profound implications for recovering lost 21 cm radial modes due to foreground subtraction and constraining primordial non-Gaussianity using the multitracer method with future cosmological surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Integral field spectroscopy of high-redshift galaxies has become a powerful tool for understanding their dynamics and evolutionary states. However, in the case of gravitationally lensed systems, it has proved difficult to model both lensing and intrinsic kinematics in a way that takes full advantage of the information available in the spectral domain. In this paper, we introduce a new method for pixel-based source reconstruction that alters standard regularization schemes for two-dimensional (2D) data in a way that leverages kinematic information in a physically motivated but flexible fashion, and that is better suited to the three-dimensional (3D) nature of integral field data. To evaluate the performance of this method, we compare its results to those of a more traditional 2D nonparametric approach using mock Atacama Large Millimeter/submillimeter Array (ALMA) observations of a typical high-redshift dusty star-forming galaxy. We find that 3D regularization applied to an entire data cube reconstructs a source’s intensity and velocity structure more accurately than 2D regularization applied to separate velocity channels. Cubes reconstructed with 3D regularization also have more uniform noise and resolution properties and are less sensitive to the signal-to-noise ratio of individual velocity channels than the results of 2D regularization. Our new approach to modeling integral field observations of lensed systems can be implemented without making restrictive a priori assumptions about intrinsic kinematics, and opens the door to new observing strategies that prioritize spectral resolution over spatial resolution (e.g., for multiconfiguration arrays like ALMA).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The current paradigm of cosmic-ray (CR) origin states that the greater part of galactic CRs is produced by supernova remnants. The interaction of supernova ejecta with the interstellar medium after a supernova's explosions results in shocks responsible for CR acceleration via diffusive shock acceleration (DSA). We use particle-in-cell (PIC) simulations and a combined PIC-magnetohydrodynamic (PIC-MHD) technique to investigate whether DSA can occur in oblique high Mach number shocks. Using the PIC method, we follow the formation of the shock and determine the fraction of the particles that gets involved in DSA. With this result, we use PIC-MHD simulations to model the large-scale structure of the plasma and the magnetic field surrounding the shock and find out whether or not the reflected particles can generate upstream turbulence and trigger DSA. We find that the feasibility of this process in oblique shocks depends strongly on the Alfvénic Mach number, and the DSA process is more likely to be triggered at high Mach number shocks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Novel insights into the behavior of the diffusion coefficients of charged particles in the inner heliosphere are of great importance to any study of the transport of these particles and are especially relevant with regard to the transport of low-energy electrons. The present study undertakes an exhaustive investigation into the diffusion parameters needed to reproduce low-energy electron intensities as observed at Earth, using a state-of-the-art 3D cosmic ray transport code. To this end, the transport of Jovian electrons is considered, as Jupiter represents the predominant source of these particles in the inner heliosphere, and because a careful comparison of model results with observations taken during periods of good and poor magnetic connectivity between Earth and Jupiter allows for conclusions to be drawn as to both parallel and perpendicular diffusion coefficients. This study then compares these results with the predictions made by various scattering theories. Best-fit parameters for parallel and perpendicular mean free paths at 1 au fall reasonably well within the span of observational values reported by previous studies, but best-fit radial and rigidity dependences vary widely. However, a large number of diffusion parameters lead to reasonable to-good fits to observations, and it is argued that considerable caution must be exercised when comparing theoretical results for diffusion coefficients with diffusion parameters calculated from particle transport studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Strong gravitational lensing of gravitational wave sources offers a novel probe of both the lens galaxy and the binary source population. In particular, the strong lensing event rate and the time-delay distribution of multiply imaged gravitational-wave binary coalescence events can be used to constrain the mass distribution of the lenses as well as the intrinsic properties of the source population. We calculate the strong lensing event rate for a range of second- (2G) and third-generation (3G) detectors, including Advanced LIGO/Virgo, A+, Einstein Telescope (ET), and Cosmic Explorer (CE). For 3G detectors, we find that ∼0.1% of observed events are expected to be strongly lensed. We predict detections of ∼1 lensing pair per year with A+, and ∼50 pairs per year with ET/CE. These rates are highly sensitive to the characteristic galaxy velocity dispersion, <jats:italic>σ</jats:italic> <jats:sub>*</jats:sub>, implying that observations of the rates will be a sensitive probe of lens properties. We explore using the time-delay distribution between multiply imaged gravitational-wave sources to constrain properties of the lenses. We find that 3G detectors would constrain <jats:italic>σ</jats:italic> <jats:sub>*</jats:sub> to ∼21% after 5 yr. Finally, we show that the presence or absence of strong lensing within the detected population provides useful insights into the source redshift and mass distribution out to redshifts beyond the peak of the star formation rate, which can be used to constrain formation channels and their relation to the star formation rate and delay-time distributions for these systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Understanding the chemical past of our Sun and how life appeared on Earth is no mean feat. The best strategy we can adopt is to study newborn stars located in an environment similar to the one in which our Sun was born and assess their chemical content. In particular, hot corinos are prime targets because recent studies have shown correlations between interstellar complex organic molecules abundances from hot corinos and comets. The ORion ALMA New GEneration Survey aims to assess the number of hot corinos in the closest and best analog to our Sun’s birth environment, the OMC-2/3 filament. In this context, we investigated the chemical nature of 19 solar-mass protostars and found that 26% of our sample sources show warm methanol emission indicative of hot corinos. Compared to the Perseus low-mass star-forming region, where the PErseus ALMA CHEmistry Survey detected hot corinos in ∼60% of the sources, the hot corinos seem to be relatively scarce in the OMC-2/3 filament. While this suggests that the chemical nature of protostars in Orion and Perseus is different, improved statistics is needed in order to consolidate this result. If the two regions are truly different, this would indicate that the environment is likely playing a role in shaping the chemical composition of protostars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Some of the major challenges faced in understanding the early evolution of coronal mass ejections (CMEs) are due to the limited observations in the inner corona (&lt;3 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>) and the plane-of-sky measurements. In this work, we have thus extended the application of the Graduated Cylindrical Shell (GCS) model to inner coronal observations from the ground-based coronagraph K-Cor of the Mauna Loa Solar Observatory, along with the pairs of observations from COR-1 on board the Solar Terrestrial Relations Observatory. We study the rapid initial acceleration and width expansion phases of five CMEs in white light at the lower heights. We also study the evolution of the modeled volumes of these CMEs in the inner corona and report, for the first time, a power-law dependence of CME volume with distance from the Sun. We further find that the volumes of the ellipsoidal leading front and the conical legs follow different power laws, thus indicating differential volume expansion throughout a CME. The study also reveals two distinct power laws for the total volume evolution of CMEs in the inner and outer corona, thus suggesting different expansion mechanisms at these different heights. Besides aiding our current understanding of CME evolution, these results will also provide better constraints to CME initiation and propagation models. Also, given the loss of the STEREO-B (and hence COR-1B data) from 2016, the modified GCS model presented here will still enable stereoscopy in the inner corona for the 3D study of CMEs in white light.</jats:p>