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<jats:title>Abstract</jats:title> <jats:p>We use a 2.5D magnetohydrodynamic model to investigate the propagation of azimuthally driven Alfvén waves with different periods and their interaction with the solar wind. In the absence of waves, the dipole field is stretched into a helmet streamer by the solar wind. The wind speeds near the equator are lower than those in the mid and high latitudes. Magnetic reconnection in the equatorial plasma sheet regularly triggers a breakup and expulsion of a plasmoid. We next inject monochromatic Alfvén waves with a moderate amplitude of 9 km s<jats:sup>−1</jats:sup> and a period of <jats:italic>τ</jats:italic> = 1000 s at the coronal base. A cavity showing features of forward and backward propagating modes is formed. The backward waves are able to accelerate the background plasma at mid and high latitudes through the nonlinear coupling to compressional waves. The size of the cavity increases with the period of the Alfvén waves as long as the outer boundary remains in the sub-Alfvénic wind. When <jats:italic>τ</jats:italic> = 4000 s, we find enhanced acceleration and heating of the solar wind plasma as well as suppression of the reconnection in the equatorial plasma sheet. The amplitudes of the backward Alfvén waves remain large inside the cavity and modify its size. The cavity ceases to exist as its outer boundary gradually moves into the super-Alfvénic wind and the large amplitude backward waves are swept away by the wind. Results suggest that Alfvén waves with moderate amplitudes can modify the dynamics and the energetics of the solar wind plasma with the embedded magnetic field.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal mass ejections (CMEs) are a major source of solar wind disturbances that affect the space plasma and magnetic field environment along their propagation path. Accurate prediction of the arrival of a CME at Earth or any point in the heliosphere is still a daunting task. In this study we explore an often overlooked factor—the effects of “pre-events” that can alter the propagation of a CME due to a preceding CME. A data-driven magnetohydrodynamic numerical model is used to simulate the propagation of multiple CMEs and their driven shocks that occurred in 2012 July. The simulation results are validated with in situ solar wind plasma and magnetic field measurements at 1 au, testing the appropriateness of our simulation results for interpreting the CME/shock evolution. By comparing the simulation results with and without preceding CMEs, we find that the trailing CME can be accelerated by the “wake” of a preceding CME. A detailed analysis suggests that the acceleration is caused partially by an increase in the background solar wind and partially by the so-called “snowplow” effect, with the latter being the major contributor for the 2012 July event.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the package <jats:sc>Gravelamps</jats:sc>, which is designed to analyze gravitationally lensed gravitational wave signals in order to constrain the mass density profile of the lensing object. <jats:sc>Gravelamps</jats:sc> does this via parameter estimation using the framework of <jats:sc>bilby</jats:sc>, which enables estimation of both the lens and the source parameters. The package can be used to study both microlensing and macrolensing cases, where the lensing mass distribution is described by a point-mass and extended-mass density profile, respectively. It allows the user to easily and freely switch between a full wave optics and approximate geometric optics description. The performance of <jats:sc>Gravelamps</jats:sc> is demonstrated via simulated analysis of both microlensing and macrolensing events, illustrating its capability for both parameter estimation and model selection in the wave optics and hybrid environments. To further demonstrate the utility of the package, the real gravitational-wave event GW170809 was analyzed using <jats:sc>Gravelamps</jats:sc>; this event was found to yield no strong evidence supporting the lensing hypothesis, consistent with previously published results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use hydrodynamical simulations of two Milky Way–mass galaxies to demonstrate the impact of cosmic-ray pressure on the kinematics of cool and warm circumgalactic gas. Consistent with previous studies, we find that cosmic-ray pressure can dominate over thermal pressure in the inner 50 kpc of the circumgalactic medium (CGM), creating an overall cooler CGM than that of similar galaxy simulations run without cosmic rays. We generate synthetic sight lines of the simulated galaxies’ CGM and use Voigt profile-fitting methods to extract ion column densities, Doppler-<jats:italic>b</jats:italic> parameters, and velocity centroids of individual absorbers. We directly compare these synthetic spectral line fits with HST/COS CGM absorption-line data analyses, which tend to show that metallic species with a wide range of ionization potential energies are often kinematically aligned. Compared to the Milky Way simulation run without cosmic rays, the presence of cosmic-ray pressure in the inner CGM creates narrower O <jats:sc>vi</jats:sc> absorption features and broader Si <jats:sc>iii</jats:sc> absorption features, a quality that is more consistent with observational data. Additionally, because the cool gas is buoyant due to nonthermal cosmic-ray pressure support, the velocity centroids of both cool and warm gas tend to align in the simulated Milky Way with feedback from cosmic rays. Our study demonstrates that detailed, direct comparisons between simulations and observations, focused on gas kinematics, have the potential to reveal the dominant physical mechanisms that shape the CGM.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper, we discuss atomic processes modifying the soft X-ray spectra from optical depth effects like photoelectric absorption and electron scattering suppressing the soft X-ray lines. We also show the enhancement in soft X-ray line intensities in a photoionized environment via continuum pumping. We quantify the suppression/enhancement by introducing a “line modification factor (<jats:italic>f</jats:italic> <jats:sub>mod</jats:sub>).” If 0 ≤ <jats:italic>f</jats:italic> <jats:sub>mod</jats:sub> ≤ 1, the line is suppressed, which could be the case in both collisionally ionized and photoionized systems. If <jats:italic>f</jats:italic> <jats:sub>mod</jats:sub> ≥ 1, the line is enhanced, which occurs in photoionized systems. Hybrid astrophysical sources are also very common, where the environment is partly photoionized and partly collisionally ionized. Such a system is V1223 Sgr, an Intermediate Polar binary. We show the application of our theory by fitting the first-order Chandra Medium Energy Grating (MEG) spectrum of V1223 Sgr with a combination of <jats:sc>Cloudy</jats:sc>-simulated additive cooling-flow and photoionized models. In particular, we account for the excess flux for O <jats:sc>vii</jats:sc>, O <jats:sc>viii</jats:sc>, Ne <jats:sc>ix</jats:sc>, Ne <jats:sc>x</jats:sc>, and Mg <jats:sc>xi</jats:sc> lines in the spectrum found in a recent study, which could not be explained with an absorbed cooling-flow model.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A recent study conducted using CALIFA survey data has found that the orbital motions of neighbor galaxies are coherent with the spin direction of a target galaxy on scales of many megaparsecs. We study this so-called “large-scale coherence” phenomenon using <jats:italic>N</jats:italic>-body cosmological simulations. We confirm a strong coherence signal within 1 Mpc <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> of a target galaxy, reaching out to 6 Mpc <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup>. We divide the simulation halos into subsamples based on mass, spin, merger history, and local halo number density for both target and neighbor halos. We find a clear dependency on the mass of the target halo only. Another key parameter is the local number density of both target and neighbor halos, with high-density regions such as clusters and groups providing the strongest coherence signals, rather than filaments or lower-density regions. However we do not find a clear dependency on halo spin or time since last major merger. The most striking result we find is that the signal can be detected up to 15 Mpc <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> from massive halos. These results provide valuable lessons on how observational studies could more clearly detect coherence, and we discuss the implications of our results for the origins of large-scale coherence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze Multi-Unit Spectroscopic Explorer observations of nine low-redshift (<jats:italic>z</jats:italic> &lt; 0.1) Palomar-Green quasar host galaxies to investigate the spatial distribution and kinematics of the warm, ionized interstellar medium, with the goal of searching for and constraining the efficiency of active galactic nucleus (AGN) feedback. After separating the bright AGN from the starlight and nebular emission, we use pixel-wise, kpc-scale diagnostics to determine the underlying excitation mechanism of the line emission, and we measure the kinematics of the narrow-line region (NLR) to estimate the physical properties of the ionized outflows. The radial size of the NLR correlates with the AGN luminosity, reaching scales of ∼5 kpc and beyond. The geometry of the NLR is well-represented by a projected biconical structure, suggesting that the AGN radiation preferably escapes through the ionization cone. We find enhanced velocity dispersions (≳100 km s<jats:sup>−1</jats:sup>) traced by the H<jats:italic>α</jats:italic> emission line in localized zones within the ionization cones. Interpreting these kinematic features as signatures of interaction between an AGN-driven ionized gas outflow and the host galaxy interstellar medium, we derive mass-outflow rates of ∼0.008–1.6 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> and kinetic injection rates of ∼10<jats:sup>39</jats:sup>–10<jats:sup>42</jats:sup> erg s<jats:sup>−1</jats:sup>, which yield extremely low coupling efficiencies of ≲10<jats:sup>−3</jats:sup>. These findings add to the growing body of recent observational evidence that AGN feedback is highly ineffective in the host galaxies of nearby AGNs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the Sloan Digital Sky Survey Data Release aperture, which has a 3″ diameter similar to COS, IFU, and long-slit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using IFU observations of three galaxies, we find that the <jats:italic>E</jats:italic>(<jats:italic>B</jats:italic> − <jats:italic>V</jats:italic>) values derived from the Balmer ratios decrease (by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.″5. We examine the relative contributions from the gas and stars using the H<jats:italic>α</jats:italic> and [O <jats:sc>iii</jats:sc>] <jats:italic>λ</jats:italic>5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the far-UV CLASSY spectra, even when narrow 1.″0 long-slit observations are used.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The radial velocity (RV) detection of exoplanets is challenged by stellar spectroscopic variability that can mimic the presence of planets and by instrumental instability that can further obscure the detection. Both stellar and instrumental changes can distort the spectral line profiles and be misinterpreted as apparent RV shifts. We present an improved FourIEr <jats:italic>phase</jats:italic> SpecTrum Analysis (FIESTA, aka <jats:italic>ϕ</jats:italic>ESTA) to disentangle apparent velocity shifts due to a line deformation from a true Doppler shift. <jats:italic>ϕ</jats:italic>ESTA projects a stellar spectrum’s cross-correlation function (CCF) onto a truncated set of Fourier basis functions. Using the amplitude and phase information from each Fourier mode, we can trace the line variability at different CCF width scales to robustly identify and mitigate multiple sources of RV contamination. For example, in our study of the 3 yr of HARPS-N solar data, <jats:italic>ϕ</jats:italic>ESTA reveals the solar rotational effect, the long-term trend due to solar magnetic cycle, instrumental instability, and apparent solar rotation rate changes. Applying a multiple linear regression model on <jats:italic>ϕ</jats:italic>ESTA metrics, we reduce the weighted rms noise from 1.89 to 0.98 m s<jats:sup>−1</jats:sup>. In addition, we observe a ∼3-day lag in the <jats:italic>ϕ</jats:italic>ESTA metrics, similar to the findings from previous studies on the bisector inverse slope and FWHM.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The mean plane-of-sky magnetic field strength is traditionally obtained from the combination of polarization and spectroscopic data using the Davis–Chandrasekhar–Fermi (DCF) technique. However, we identify the major problem of the DCF technique to be its disregard of the anisotropic character of MHD turbulence. On the basis of the modern MHD turbulence theory we introduce a new way of obtaining magnetic field strength from observations. Unlike the DCF technique, the new technique uses not the dispersion of the polarization angle and line-of-sight velocities, but increments of these quantities given by the structure functions. To address the variety of astrophysical conditions for which our technique can be applied, we consider turbulence in both media with magnetic pressure higher than the gas pressure, corresponding, e.g., to molecular clouds, and media with gas pressure higher than the magnetic pressure, corresponding to the warm neutral medium. We provide general expressions for arbitrary admixtures of Alfvén, slow, and fast modes in these media and consider in detail particular cases relevant to diffuse media and molecular clouds. We successfully test our results using synthetic observations obtained from MHD turbulence simulations. We demonstrate that our differential measure approach, unlike the DCF technique, can be used to measure the distribution of magnetic field strengths, can provide magnetic field measurements with limited data, and is much more stable in the presence of induced large-scale variations of nonturbulent nature. Furthermore, our study uncovers the deficiencies of earlier DCF research.</jats:p>