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<jats:title>Abstract</jats:title> <jats:p>Periodic outbursts are observed in several changing-look (CL) active galactic nuclei (AGNs). Sniegowska et al. suggested a model to explain the repeating CL in these AGNs, where the periodic outbursts are triggered in a narrow unstable zone between an inner advection-dominated accretion flow and outer thin disk. In this work, we intend to investigate the effects of large-scale magnetic fields on the limit cycle behaviors of CL AGNs. The winds driven by magnetic fields can significantly change the structure of thin disk by taking away the angular momentum and energy of the disk. It is found that the period of outburst in repeating CL AGNs can be substantially reduced by the magnetic fields. Conversely, if we keep the period unchanged, the outburst intensity can be raised by several times. These results can help to explain the observational properties of multiple CL AGNs. Besides the magnetic fields, the effects of transition radius <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\mathrm{tr}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe766ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, the width of the transition zone Δ<jats:italic>R</jats:italic>, and the Shakura–Sunyaev parameter <jats:italic>α</jats:italic> are also explored in this work.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper systematically investigates the comoving megaparsec-scale intergalactic medium (IGM) environment around galaxies traced by the Ly<jats:italic>α</jats:italic> forest. Using our cosmological hydrodynamic simulations, we investigate the IGM–galaxy connection at <jats:italic>z</jats:italic> = 2 by two methods: (i) cross-correlation analysis between galaxies and the fluctuation of Ly<jats:italic>α</jats:italic> forest transmission (<jats:italic>δ</jats:italic> <jats:sub>F</jats:sub>) and (ii) comparison of the overdensity of neutral hydrogen (H <jats:sc>i</jats:sc>) and galaxies. Our simulations reproduce observed cross-correlation functions (CCFs) between Ly<jats:italic>α</jats:italic> forest and Lyman-break galaxies. We further investigate the variation of the CCF using subsamples divided by dark matter halo mass (<jats:italic>M</jats:italic> <jats:sub>DH</jats:sub>), galaxy stellar mass (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>), and star formation rate (SFR) and find that the CCF signal becomes stronger with increasing <jats:italic>M</jats:italic> <jats:sub>DH</jats:sub>, <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>, and SFR. The CCFs between galaxies and gas density fluctuation are also found to have similar trends. Therefore, the variation of <jats:italic>δ</jats:italic> <jats:sub>F</jats:sub>–CCF depending on <jats:italic>M</jats:italic> <jats:sub>DH</jats:sub>, <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>, and SFR is due to varying gas densities around galaxies. We find that the correlation between galaxies and the IGM H <jats:sc>i</jats:sc> distribution strongly depends on <jats:italic>M</jats:italic> <jats:sub>DH</jats:sub> as expected from linear theory. Our results support the ΛCDM paradigm, confirming a spatial correlation between galaxies and IGM H <jats:sc>i</jats:sc>, with more massive galaxies being clustered in higher-density regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A range of cosmological observations demonstrate an accelerated expansion of the universe, and the most likely explanation of this phenomenon is a cosmological constant. Given the importance of understanding the underlying physics, it is relevant to investigate alternative models. This article uses numerical simulations to test the consistency of one such alternative model. Specifically, this model has no cosmological constant; instead, the dark matter particles have an extra force proportional to the velocity squared, somewhat reminiscent of the magnetic force in electrodynamics. The constant strength of the force is the only free parameter. Because bottom-up structure formation creates cosmological structures whose internal velocity dispersions increase in time, this model may mimic the temporal evolution of the effect from a cosmological constant. It is shown that models with force linearly proportional to internal velocities, or models proportional to velocity to power 3 or more, cannot mimic the accelerated expansion induced by a cosmological constant. However, models proportional to velocity squared are still consistent with the temporal evolution of a universe with a cosmological model.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present bright [C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m line detections from a strongly magnified and multiply imaged (<jats:italic>μ</jats:italic> ∼ 20–160) sub–<jats:italic>L</jats:italic> <jats:sup>*</jats:sup> (<jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{UV}}=-{19.75}_{-0.44}^{+0.55}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>UV</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>19.75</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.44</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.55</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd7ecieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) Lyman-break galaxy (LBG) at <jats:italic>z</jats:italic> = 6.0719 ± 0.0004, drawn from the ALMA Lensing Cluster Survey (ALCS). Emission lines are identified at 268.7 GHz at ≥8<jats:italic>σ</jats:italic> exactly at the positions of two multiple images of the LBG, behind the massive galaxy cluster RXCJ0600−2007. Our lens models, updated with the latest spectroscopy from VLT/MUSE, indicate that a sub region of the LBG crosses the caustic, and is lensed into a long (∼6″) arc with a local magnification of <jats:italic>μ</jats:italic> ∼ 160, for which the [C <jats:sc>ii</jats:sc>] line is also significantly detected. The source plane reconstruction resolves the interstellar medium (ISM) structure, showing that the [C <jats:sc>ii</jats:sc>] line is co-spatial with the rest-frame UV continuum at a scale of ∼300 pc. The [C <jats:sc>ii</jats:sc>] line properties suggest that the LBG is a rotation-dominated system, whose velocity gradient explains a slight difference in redshifts between the whole LBG and its sub-region. The star formation rate (SFR)–<jats:italic>L</jats:italic> <jats:sub>[CII]</jats:sub> relations, for whole and sub-regions of the LBG, are consistent with those of local galaxies. We evaluate the lower limit of the faint-end of the [C <jats:sc>ii</jats:sc>] luminosity function at <jats:italic>z</jats:italic> = 6, finding it to be consistent with predictions from semi-analytical models and from the local SFR–<jats:italic>L</jats:italic> <jats:sub>[CII]</jats:sub> relation with a SFR function at <jats:italic>z</jats:italic> = 6. These results imply that the local SFR–<jats:italic>L</jats:italic> <jats:sub>[CII]</jats:sub> relation is universal for a wide range of scales, including the spatially resolved ISM, the whole region of the galaxy, and the cosmic scale, even in the epoch of reionization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on galactic cosmic ray (GCR) and plasma observations from the ACE spacecraft, in this work, we analyze the relation between the GCR counts and the solar wind parameters during two recent two solar minima (for the years 2007.0–2009.0, and 2016.5–2018.5) by means of the superposed epoch analysis (SEA) method. The results indicate that GCRs are strongly modulated by the co-rotating interaction regions (CIRs) in the solar wind, and that the occurrences of stream interfaces (SIs) between fast and slow solar wind are correlated with a depression in GCR counts. The so-called “snow plow” effect of GCR variation prior to SI crossing appears during the first solar minimum, and the GCR counts decrease after the crossing, corresponding to a sudden drop in the diffusion coefficient at the SIs. The gradient of GCR counts shows that the transport efficiency of GCRs is low (high), relative to slow (fast) solar wind. However, during the second solar minimum, we see a completely opposite scenario; the “snow plow” effect is not observed, and GCR transport becomes faster in slow solar wind, and slower in fast solar wind. In addition, heliospheric current-sheet crossings also correlate with GCR counts. Particles drift along the current sheet, then accumulate in a pileup structure, where diffusion and drift effects may be balanced. It is found that the drift effect rivals the diffusion and convection on the GCR transport at 1 au during the two solar minima.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present integral field spectroscopic observations of the nearby (<jats:italic>z</jats:italic> ∼ 0.03) dual active galactic nuclei (AGNs) Mrk 739, whose projected nuclear separation is ∼3.4 kpc, obtained with the Multi Unit Spectroscopic Explorer at the Very Large Telescope. We find that the galaxy has an extended AGN-ionized emission-line region extending up to ∼20 kpc away from the nuclei, while star-forming regions are more centrally concentrated within 2–3 kpc. We model the kinematics of the ionized gas surrounding the eastern nucleus using a circular disk profile, resulting in a peak velocity of <jats:inline-formula> <jats:tex-math> <?CDATA ${237}_{-28}^{+26}\,\mathrm{km}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>237</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>28</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>26</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mi>km</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabedbaieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at a distance of ∼1.2 kpc. The enclosed dynamical mass within 1.2 kpc is <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}M({M}_{\odot })=10.20\pm 0.06$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>M</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>10.20</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.06</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabedbaieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, ∼1000 times larger than the estimated supermassive black hole (SMBH) mass of Mrk 739E. The morphology and dynamics of the system are consistent with an early stage of the collision, where the foreground galaxy (Mrk 739W) is a young star-forming galaxy in an ongoing first passage with its background companion (Mrk 739E). Since the SMBH in Mrk 739W does not show evidence of being rapidly accreting, we claim that the northern spiral arms of Mrk 739W are ionized by the nuclear activity of Mrk 739E.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Blazars are potential sources of cosmic-ray acceleration up to ultrahigh energies (<jats:italic>E</jats:italic> ≳ 10<jats:sup>18</jats:sup> eV). For an efficient cosmic-ray injection from blazars, <jats:italic>pγ</jats:italic> collisions with extragalactic background light (EBL) and cosmic microwave background (CMB) can produce neutrino spectra with peaks near to PeV and EeV energies, respectively. In this work, we analyze the contribution of these neutrinos to the diffuse background measured by the IceCube neutrino observatory. The fraction of neutrino luminosity originating from individual redshift ranges is calculated using the distribution of BL Lacs and FSRQs provided in the Fermi-LAT 4LAC catalog. Furthermore, we use a luminosity-dependent density evolution to find the neutrino flux of unresolved blazars. The results obtained in our model indicate that as much as ≈10% of the flux upper bound at a few PeV energies can arise from cosmic-ray interactions with EBL. The same interactions will also produce secondary electrons and photons, initiating electromagnetic cascades. The resultant photon spectrum is limited by the isotropic diffuse <jats:italic>γ</jats:italic>-ray flux measured between 100 MeV and 820 GeV. The latter, together with the observed cosmic-ray flux at <jats:italic>E</jats:italic> &gt; 10<jats:sup>16.5</jats:sup> eV, can constrain the baryonic loading factor, depending on the maximum cosmic-ray acceleration energy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thorne–Żytkow objects (TŻOs) are a class of stellar object comprised of a neutron star core surrounded by a large and diffuse envelope. Their exterior appearance is identical to red supergiants; the distinctive electromagnetic signature of a TŻO is a suite of unusual chemical abundance patterns, including excesses of Li, Rb, Mo, and Ca. However, electromagnetic observations cannot unambiguously identify the presence of a neutron star core. Detection of continuous gravitational wave emission from a rotating neutron star core would provide strong supporting evidence for the existence of TŻOs. We present a model for gravitational wave detector confirmation of TŻOs and demonstrate that these objects should be detectable with Advanced LIGO. We also investigate possible targets for joint optical and gravitational searches, and comment on prospects for detectability in both current and future gravitational wave detector networks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Periodic quasars have been suggested to host supermassive binary black holes (BBHs) in their centers, and their optical/UV periodicities are interpreted as caused by either the Doppler-boosting (DB) effect of continuum emission from the disk around the secondary black hole (BH) or intrinsic accretion rate variation. However, no other definitive evidence has been found to confirm such a BBH interpretation(s). In this paper, we investigate the responses of broad emission lines (BELs) to the continuum variations for these quasars under two BBH scenarios and check whether they can be distinguished from each other and from that of a single BH system. We assume a simple circumbinary broad-line region (BLR) model, compatible with BLR size estimates, with a standard Γ distribution of BLR clouds. We find that BELs may change significantly and periodically under the BBH scenarios due to (1) the position variation of the secondary BH and (2) the DB effect, if significant, and/or intrinsic variation, which is significantly different from the case of a single BH system. For the two BBH scenarios, the responses of BELs to (apparent) continuum variations, caused by the DB effect or intrinsic rate variation, are also significantly different from each other, mainly because the DB effect has a preferred direction along the direction of motion of the secondary BH, while that due to intrinsic variation does not. Such differences in the responses of BELs from different scenarios may offer a robust way to distinguish different interpretations of periodic quasars and to identify BBHs, if any, in these systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Fast radio bursts (FRBs) can be scattered by ionized gas in their local environments, host galaxies, intervening galaxies along their lines of sight (LOS), the intergalactic medium, and the Milky Way. The relative contributions of these different media depend on their geometric configuration and the internal properties of the gas. When these relative contributions are well understood, FRB scattering is a powerful probe of density fluctuations along the LOS. The precise scattering measurements for <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="FRB 121102" xlink:type="simple">FRB 121102</jats:named-content> and <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="FRB 180916" xlink:type="simple">FRB 180916</jats:named-content> allow us to place an upper limit on the amount of scattering contributed by the Milky Way halo to these FRBs. The scattering time <jats:inline-formula> <jats:tex-math> <?CDATA $\tau \propto (\widetilde{F}\times {\mathrm{DM}}^{2}){A}_{\tau }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>τ</mml:mi> <mml:mo>∝</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mover accent="true"> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">˜</mml:mo> </mml:mrow> </mml:mover> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mi>DM</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:msub> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabeb6eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where DM is the dispersion measure, <jats:inline-formula> <jats:tex-math> <?CDATA $\widetilde{F}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>F</mml:mi> </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="apjabeb6eieqn2.gif" xlink:type="simple" /> </jats:inline-formula> quantifies electron density variations with <jats:inline-formula> <jats:tex-math> <?CDATA $\widetilde{F}=0$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">˜</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabeb6eieqn3.gif" xlink:type="simple" /> </jats:inline-formula> for a smooth medium, and the dimensionless constant <jats:italic>A</jats:italic> <jats:sub> <jats:italic>τ</jats:italic> </jats:sub> quantifies the difference between the mean scattering delay and the 1/<jats:italic>e</jats:italic> scattering time typically measured. A likelihood analysis of the observed scattering and halo DM constraints finds that <jats:inline-formula> <jats:tex-math> <?CDATA $\widetilde{F}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>F</mml:mi> </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="apjabeb6eieqn4.gif" xlink:type="simple" /> </jats:inline-formula> is at least an order of magnitude smaller in the halo than in the Galactic disk. The maximum pulse broadening from the halo is <jats:italic>τ</jats:italic> ≲ 12 <jats:italic>μ</jats:italic>s at 1 GHz. We compare our analysis of the Milky Way halo with other galaxy halos by placing limits on the scattering contributions from halos intersecting the LOS to <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="FRB 181112" xlink:type="simple">FRB 181112</jats:named-content> and <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="FRB 191108" xlink:type="simple">FRB 191108</jats:named-content>. Our results are consistent with halos making negligible or very small contributions to the scattering times of these FRBs.</jats:p>