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<jats:title>Abstract</jats:title> <jats:p>Using a combination of general-relativistic magnetohydrodynamics simulations and ray tracing of synchrotron emission, we study the effect of modest (24°) misalignment between the black hole spin and plasma angular momentum, focusing on the variability of total flux, image centroids, and image sizes. We consider both millimeter and infrared (IR) observables motivated by Sagittarius A* (Sgr A*), though our results apply more generally to optically thin flows. For most quantities, tilted accretion is more variable, primarily due to a significantly hotter and denser <jats:italic>coronal</jats:italic> region well off the disk midplane. We find (1) a 150% increase in millimeter light-curve variability when adding tilt to the flow; (2) the tilted image centroid in the millimeter shifts on a scale of 3.7 <jats:italic>μ</jats:italic>as over 28 hr (5000 gravitational times) for some electron temperature models; (3) tilted disk image diameters in the millimeter can be 10% larger (52 versus 47 <jats:italic>μ</jats:italic>as) than those of aligned disks at certain viewing angles; (4) the tilted models produce significant IR flux, similar to that seen in Sgr A*, with comparable or even greater variability than observed; and (5) for some electron models, the tilted IR centroid moves by more than 50 <jats:italic>μ</jats:italic>as over several hours, in a similar fashion to the centroid motion detected by the GRAVITY interferometer.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The extragalactic background light (EBL) consists of integrated light from all sources of emission throughout the history of the universe. At near-infrared wavelengths, the EBL is dominated by stellar emission across cosmic time; however, the spectral and redshift information of the emitting sources is entangled and cannot be directly measured by absolute photometry or fluctuation measurements. Cross-correlating near-infrared maps with tracers of known redshift enables EBL redshift tomography, as EBL emission will only correlate with external tracers from the same redshift. Here, we forecast the sensitivity of probing the EBL spectral energy distribution as a function of redshift by cross-correlating the upcoming near-infrared spectro-imaging survey, SPHEREx, with several current and future galaxy redshift surveys. Using a model galaxy luminosity function, we estimate the cross power spectrum clustering amplitude on large scales, and forecast that the near-infrared EBL spectrum can be detected tomographically out to <jats:italic>z</jats:italic> ∼ 6. We also predict a high-significance measurement (∼10<jats:sup>2</jats:sup>–10<jats:sup>4</jats:sup> <jats:italic>σ</jats:italic>) of the small-scale cross power spectrum out to <jats:italic>z</jats:italic> ∼ 10. The amplitudes of the large-scale cross power spectra can constrain the cosmic evolution of the stellar synthesis process through both continuum and the line emission, while on the nonlinear and Poisson noise scales, the high-sensitivity measurements can probe the mean spectra associated with the tracer population across redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Line intensity mapping (LIM) is emerging as a powerful technique to map the cosmic large-scale structure and to probe cosmology over a wide range of redshifts and spatial scales. We perform Fisher forecasts to determine the optimal design of wide-field ground-based millimeter-wavelength LIM surveys for constraining properties of neutrinos and light relics. We consider measuring the auto-power spectra of several CO rotational lines (from <jats:italic>J</jats:italic> = 2–1 to <jats:italic>J</jats:italic> = 6–5) and the [C <jats:sc>ii</jats:sc>] fine-structure line in the redshift range of 0.25 &lt; <jats:italic>z</jats:italic> &lt; 12. We study the constraints with and without interloper lines as a source of noise in our analysis, and for several one-parameter and multiparameter extensions of ΛCDM. We show that LIM surveys deployable this decade, in combination with existing cosmic microwave background (CMB; primary) data, could achieve order-of-magnitude improvements over Planck constraints on <jats:italic>N</jats:italic> <jats:sub>eff</jats:sub> and <jats:italic>M</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub>. Compared to next-generation CMB and galaxy surveys, a LIM experiment of this scale could achieve bounds that are a factor of ∼3 better than those forecasted for surveys such as EUCLID (galaxy clustering), and potentially exceed the constraining power of CMB-S4 by a factor of ∼1.5 and ∼3 for <jats:italic>N</jats:italic> <jats:sub>eff</jats:sub> and <jats:italic>M</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub>, respectively. We show that the forecasted constraints are not substantially affected when enlarging the parameter space, and additionally demonstrate that such a survey could also be used to measure ΛCDM parameters and the dark energy equation of state exquisitely well.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The helium abundance, defined as <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> = <jats:italic>n</jats:italic> <jats:sub>He</jats:sub>/<jats:italic>n</jats:italic> <jats:sub>H</jats:sub> × 100, is ∼8.5 in the photosphere and seldom exceeds 5 in fast solar wind. Previous statistics have demonstrated that <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> in slow solar wind correlates tightly with sunspot number. However, less attention is paid to the solar cycle dependence of <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> within interplanetary coronal mass ejections (ICMEs) and comparing the <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> characteristics of ICMEs and solar wind. In this paper we conduct a statistical comparison of helium abundance between ICMEs and solar wind near 1 au with observations of the Advanced Composition Explorer from 1998 to 2019 and find that the ICME <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> also exhibits the obvious solar cycle dependence. Meanwhile, we find that the <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> is obviously higher within ICMEs compared to solar wind, and the means within 37% and 12% of ICMEs exceed 5 and 8.5, respectively. It is interesting to answer where and how the high helium abundance originates. Our statistics demonstrate that 21% (3%) of ICME (slow wind) <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> data points exceed 8.5 around solar maximum, which decreases dramatically near minimum, while no such high <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> values appear in the fast wind throughout the whole solar cycle. This indicates that the high <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> (e.g., &gt;8.5) emanates from active regions as more ICMEs and slow wind originate from active regions around maximum, and it supports that both active regions and quiet-Sun regions are the sources of slow wind. We suggest that the high <jats:italic>A</jats:italic> <jats:sub>He</jats:sub> from active regions could be explained by means of the magnetic loop confinement model and/or photoionization effect.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The solar coronal heating in quiet Sun (QS) and coronal holes (CHs), including solar wind formation, are intimately tied by magnetic field dynamics. Thus, a detailed comparative study of these regions is needed to understand the underlying physical processes. CHs are known to have subdued intensity and larger blueshifts in the corona. This work investigates the similarities and differences between CHs and QS in the chromosphere using the Mg <jats:sc>ii</jats:sc> h and k, C <jats:sc>ii</jats:sc> line, and transition region using Si <jats:sc>iv</jats:sc> line, for regions with identical absolute magnetic flux density (∣B∣). We find CHs to have subdued intensity in all of the lines, with the difference increasing with line formation height and ∣B∣. The chromospheric lines show excess upflows and downflows in CH, while Si <jats:sc>iv</jats:sc> shows excess upflows (downflows) in CHs (QS), where the flows increase with ∣B∣. We further demonstrate that the upflows (downflows) in Si <jats:sc>iv</jats:sc> are correlated with both upflows and downflows (only downflows) in the chromospheric lines. CHs (QS) show larger Si IV upflows (downflows) for similar flows in the chromosphere, suggesting a common origin to these flows. These observations may be explained due to impulsive heating via interchange (closed-loop) reconnection in CHs (QS), resulting in bidirectional flows at different heights, due to differences in magnetic field topologies. Finally, the kinked field lines from interchange reconnection may be carried away as magnetic field rotations and observed as switchbacks. Thus, our results suggest a unified picture of solar wind emergence, coronal heating, and near-Sun switchback formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Type Iax supernovae (SNe Iax) represent the largest class of peculiar white dwarf supernovae. The type Iax SN 2012Z in NGC 1309 is the only white dwarf supernova with a detected progenitor system in pre-explosion observations. Deep Hubble Space Telescope (HST) images taken before SN 2012Z show a luminous, blue source that we have interpreted as a helium-star companion (donor) to the exploding white dwarf. We present here late-time HST observations taken ∼1400 days after the explosion to test this model. We find the SN light curve can empirically be fit by an exponential-decay model in magnitude units. The fitted asymptotic brightness is within 10% of our latest measurements and approximately twice the brightness of the pre-explosion source. The decline of the light curve is too slow to be powered by <jats:sup>56</jats:sup>Co or <jats:sup>57</jats:sup>Co decay: if radioactive decay is the dominate power source, it must be from longer half-life species like <jats:sup>55</jats:sup>Fe. Interaction with circumstellar material may contribute to the light curve, as may shock heating of the companion star. Companion-star models underpredict the observed flux in the optical, producing most of their flux in the UV at these epochs. A radioactively heated bound remnant, left after only a partial disruption of the white dwarf, is also capable of producing the observed excess late-time flux. Our analysis suggests that the total ejecta + remnant mass is consistent with the Chandrasekhar mass for a range of SNe Iax.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Physical and chemical properties of the interstellar medium (ISM) at subgalactic (∼kiloparsec) scales play an indispensable role in controlling the ability of gas to form stars. In this paper, we use the TNG50 cosmological simulation to explore the physical parameter space of eight resolved ISM properties in star-forming regions to constrain the areas of this hyperspace where most star-forming environments exist. We deconstruct our simulated galaxies spanning a wide range of mass (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> = 10<jats:sup>7</jats:sup>–10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) and redshift (0 ≤ <jats:italic>z</jats:italic> ≤ 3) into kiloparsec-sized regions and statistically analyze the gas/stellar surface densities, gas metallicity, vertical stellar velocity dispersion, epicyclic frequency, and dark-matter volumetric density representative of each region in the context of their star formation activity and environment (radial galactocentric location). By examining the star formation rate (SFR) weighted distributions of these properties, we show that stars primarily form in two distinct environmental regimes, which are brought about by an underlying bicomponent radial SFR profile in galaxies. We examine how the relative prominence of these regimes depends on galaxy mass and cosmic time. We also compare our findings with those from integral field spectroscopy observations and find similarities as well as departures. Further, using dimensionality reduction, we characterize the aforementioned hyperspace to reveal a high degree of multicollinearity in relationships among ISM properties that drive the distribution of star formation at kiloparsec scales. Based on this, we show that a reduced 3D representation underpinned by a multivariate radius relationship is sufficient to capture most of the variance in the original 8D space.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The optical radiation emitted by blazars contains contributions from synchrotron radiation by relativistic electrons in the jets, as well as thermal radiation emitted mainly by the accretion disk (AD), the broad-line region (BLR), and the host galaxy. The unpolarized radiation components from the AD, BLR, and host galaxy present themselves by decreasing the total polarization in the optical/ultraviolet (UV) spectrum. A combined model for the spectral energy distribution (SED) and degree of optical/UV polarization is constructed, enabling the disentanglement of the synchrotron and AD components. Our model is applied to the multiwavelength SED and spectropolarimetry observations of the flat-spectrum radio quasar 4C+01.02 (<jats:italic>z</jats:italic> = 2.1) in its 2016 July–August flaring state and 2017 July–August quiescent state, using data from the Fermi Large Area Telescope, the Southern African Large Telescope, and the Las Cumbres Observatory network of telescopes. By constraining the AD component, the mass of the supermassive black hole is obtained as ∼3 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Furthermore, the model retrieves the characteristics of the relativistic electron distribution in the jet and the degree of ordering of the magnetic field. Our results highlight the potential of spectropolarimetry observations for disentangling thermal from nonthermal (jet) emission components, thus revealing the physics of particle acceleration and high-energy emission in active galactic nucleus jets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The very-high-energy (VHE; <jats:italic>E</jats:italic> &gt; 100 GeV) gamma-ray emission observed from a number of supernova remnants (SNRs) indicates particle acceleration to high energies at the shock of the remnants and a potentially significant contribution to Galactic cosmic rays. It is extremely difficult to determine whether protons (through hadronic interactions and subsequent pion decay) or electrons (through inverse Compton scattering on ambient photon fields) are responsible for this emission. For a successful diagnostic, a good understanding of the spatial and energy distribution of the underlying particle population is crucial. Most SNRs are created in core-collapse explosions and expand into the wind bubble of their progenitor stars. This circumstellar medium features a complex spatial distribution of gas and magnetic field which naturally strongly affects the resulting particle population. In this work, we conduct a detailed study of the spectro-spatial evolution of the electrons accelerated at the forward shock of core-collapse SNRs and their nonthermal radiation, using the RATPaC code that is designed for the time- and spatially dependent treatment of particle acceleration at SNR shocks. We focus on the impact of the spatially inhomogeneous magnetic field through the efficiency of diffusion and synchrotron cooling. It is demonstrated that the structure of the circumstellar magnetic field can leave strong signatures in the spectrum and morphology of the resulting nonthermal emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Metric and decametric radio emissions from the Sun are the only direct source of information about the dynamics of nonthermal electrons in the upper corona. In addition, the combination of spectral and imaging (sizes, shapes, and positions) observations of low-frequency radio sources can be used as a unique diagnostic tool to probe plasma turbulence in the solar corona and inner heliosphere. The geometry of the low-frequency sources and its variation with frequency are still not understood, primarily due to the relatively low spatial resolution available for solar observations. Here we report the first detailed multifrequency analysis of the sizes of solar radio sources observed by the Low Frequency Array. Furthermore, we investigate the source shapes by approximating the derived intensity distributions using 2D Gaussian profiles with elliptical half-maximum contours. These measurements have been made possible by a novel empirical method for evaluating the instrumental and ionospheric effects on radio maps based on known source observations. The obtained deconvolved sizes of the sources are found to be smaller than previous estimations, and often show higher ellipticity. The sizes and ellipticities of the sources inferred using 2D Gaussian approximation, and their variation with frequency are consistent with models of anisotropic radio-wave scattering in the solar corona.</jats:p>