Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The quantum mechanical treatment of quadrupole radiation due to bremsstrahlung exact to all orders in the Coulomb interaction of two nonrelativistically colliding charged spin-0 and unpolarized spin-1/2 particles is presented. We calculate the elements of the quadrupole tensor, and present analytical solutions for the double-differential photon emission cross section of identical and nonidentical particles. Contact is made to Born-level and quasi-classical results in the respective kinematic limits and effective energy loss rates are obtained. A generally valid formula for soft-photon emission is established and an approximate formula across the entire kinematic regime is constructed. The results apply to bremsstrahlung emission in the scattering of pairs of electrons and are hence relevant in the study of astrophysical phenomena. A definition of a Gaunt factor is proposed which should facilitate broad applicability of the results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Spiral arms are distinctive features of many circumstellar disks, observed in scattered light, which traces the disk surface; millimeter dust emission, which probes the disk midplane; as well as molecular emission. The two leading explanations for spirals are wakes generated by a massive planet and the density waves excited by disk self-gravity. We use stratified 3D hydrodynamic shearing-box simulations including dust particles and disk self-gravity to investigate how gas and dust spirals in a self-gravitating disk depend on the simulation size, the cooling efficiency, and the aerodynamic properties of particles. We find that the opening angles of spirals are universal (∼10°) and not significantly affected by the size of the computational domain, the cooling time, or the particle size. In simulations with the biggest domain, the spirals in the gaseous disk become slightly more open with a higher cooling efficiency. Small dust follows the gaseous spirals very well, while intermediate-sized dust with dimensionless stopping time (St) close to 1 is more concentrated in the spirals and shows stronger spirals. However, large dust with St &gt; 1 also shows spirals, which is different from some previous simulations. We identify that this is due to the gravity from the gas to the dust component. We show that when St ≳ <jats:italic>Q</jats:italic>, the gravitational force from the gaseous spirals on the dust particles becomes stronger than the particles’ aerodynamic drag force, so that the gas significantly affects these large particles through gravitational interaction. This has important implications for both spiral observations and planetesimal formation/dynamics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations suggest that protoplanetary disks have moderate accretion rates onto the central young star, especially at early stages (e.g., HL Tau), indicating moderate disk turbulence. However, recent ALMA observations suggest that dust is highly settled, implying weak turbulence. Motivated by such tension, we carry out 3D stratified local simulations of self-gravitating disks, focusing on the settling of dust particles in actively accreting disks. We find that gravitationally unstable disks can have moderately high accretion rates while maintaining a relatively thin dust disk for two reasons. First, accretion stress from the self-gravitating spirals (self-gravity stress) can be stronger than the stress from turbulence (Reynolds stress) by a factor of 5–20. Second, the strong gravity from the gas to the dust decreases the dust scale height by another factor of ∼2. Furthermore, the turbulence is slightly anisotropic, producing a larger Reynolds stress than the vertical dust diffusion coefficient. Thus, gravitoturbulent disks have unusually high vertical Schmidt numbers (Sc<jats:sub> <jats:italic>z</jats:italic> </jats:sub>) if we scale the total accretion stress with the vertical diffusion coefficient (e.g., Sc<jats:sub> <jats:italic>z</jats:italic> </jats:sub> ∼ 10–100). The reduction of the dust scale height by the gas gravity should also operate in gravitationally stable disks (<jats:italic>Q</jats:italic> &gt; 1). Gravitational forces between particles become more relevant for the concentration of intermediate dust sizes, forming dense clouds of dust. After comparing with HL Tau observations, our results suggest that self-gravity and gravity among different disk components could be crucial for solving the conflict between the protoplanetary disk accretion and dust settling, at least at the early stages.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Astronomers derive MOdified Newtonian Dynamics (MOND) rotation curves using the simple algebraic rule of calculating the acceleration as equal to the Newtonian acceleration (<jats:italic>a</jats:italic>) divided by some factor <jats:italic>μ</jats:italic>(<jats:italic>a</jats:italic>). However, there are velocity differences between this simple rule and the calculation derived from more sophisticated MOND versions such as AQUAL or QMOND, created to expand MOND heuristic law and preserve the conservation of momentum, angular momentum, and energy, and follow the weak equivalence principle. Here we provide recipes based on Milgrom’s proposal to calculate semianalytically (without numerical simulations) MOND rotation curves for any density distribution based on AQUAL, applying it to different models of thin disks. The application of this formalism is equivalent to the creation of a fictitious phantom mass whose field may be used in a Newtonian way to calculate iteratively the MOND accelerations. In most cases, the differences between the application of the simple algebraic rule and the AQUAL-MOND calculations are small, ≲5%. However, the error of the algebraic solution is larger than 5% when more than half of the mass is in the MONDian regime (where Newtonian and MOND rotation speeds differ by more than 10%), reaching in some cases &gt;70% discrepancy, such as in Maclaurin disks, representative of galaxies for which the rotational velocity rises to the edge of the disk as is seen in irregular galaxies. The slope of the rotation speed in the dependence with the radius or the vertical distance of the plane is also significantly changed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an X-ray through submillimeter observations of the classical RV Tauri (RVb-type) variable U Mon, a post-asymptotic giant branch (AGB) binary with a circumbinary disk (CBD). Our SMA observations indicate a CBD diameter of ≲550 au. Our XMM-Newton observations make U Mon the first RV Tauri variable detected in X-rays. The X-ray emission is characteristic of a hot plasma (∼10 MK), with <jats:italic>L</jats:italic> <jats:sub>X</jats:sub> =5 × 10<jats:sup>30</jats:sup> erg s<jats:sup>−1</jats:sup>, and we consider its possible origin from U Mon, its companion, and/or binary system interactions. Combining DASCH and AAVSO data, we extend the time-series photometric baseline back to the late 1880s and find evidence that U Mon has secular changes that appear to recur on a timescale of ∼60 yr, possibly caused by a feature in the CBD. From literature radial velocities we find that the binary companion is a ∼2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> A-type main-sequence star. The orientation of the binary’s orbit lies along our line of sight (<jats:italic>ω</jats:italic> = 95°), such that apastron corresponds to photometric RVb minima, consistent with the post-AGB star becoming obscured by the near side of the CBD. In addition, we find the size of the inner-CBD hole (∼4.5–9 au) to be comparable to the binary separation, implying that one or both stars may interact with the CBD at apastron. The obscuration of the post-AGB star implicates the companion as the likely source of the enhanced H<jats:italic>α</jats:italic> observed at RVb minima and of the X-ray emission that may arise from accreted material.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of the low-mass satellites in the Local Group have shown high fractions of gas-poor, quiescent galaxies relative to isolated dwarfs, implying that the host halo environment plays an important role in the quenching of dwarf galaxies. In this work, we present measurements of the quenched fractions and quenching timescales of dwarf satellite galaxies in the DC Justice League suite of four high-resolution cosmological zoom-in simulations of Milky Way–mass halos. We show that these simulations accurately reproduce the satellite luminosity functions of observed nearby galaxies, as well as the variation in satellite quenched fractions from <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ∼ 10<jats:sup>5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> to 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We then trace the histories of satellite galaxies back to <jats:italic>z</jats:italic> ∼ 15 and find that many satellites with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ∼ 10<jats:sup>6</jats:sup>−10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> quench within ∼2 Gyr of infall into the host halo, while others in the same mass range remain star-forming for as long as 5 Gyr. We show that this scatter can be explained by the satellite’s gas mass and the ram pressure it feels at infall. Finally, we identify a characteristic stellar mass scale of 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> above which infalling satellites are largely resistant to rapid environmental quenching.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We solve the 2D hydrodynamic equations of hot accretion flow in the presence of the thermal conduction. The flow is assumed to be in steady state and axisymmetric, and a self-similar approximation is adopted in the radial direction. In this hydrodynamic study, we consider the viscous stress tensor to mimic the effects of the magnetorotational instability for driving angular momentum. We impose the physical boundary conditions at both the rotation axis and the equatorial plane and obtain the solutions in the full <jats:italic>r</jats:italic> −<jats:italic>θ</jats:italic> space. We have found that thermal conduction is an indispensable term for investigating the inflow-wind structure of the hot accretion flows with very low mass accretion rates. One of the most interesting results here is that the disk is convectively stable in hot accretion mode and in the presence of the thermal conduction. Furthermore, the properties of wind and also its driving mechanisms are studied. Our analytical results are consistent with previous numerical simulations of hot accretion flow.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the results from an observing campaign to confirm the peculiar motion of the supermassive black hole (SMBH) in J0437+2456 first reported in Pesce et al. Deep observations with the Arecibo Observatory have yielded a detection of neutral hydrogen (H <jats:sc>i</jats:sc>) emission, from which we measure a recession velocity of 4910 km s<jats:sup>−1</jats:sup> for the galaxy as a whole. We have also obtained near-infrared integral field spectroscopic observations of the galactic nucleus with the Gemini North telescope, yielding spatially resolved stellar and gas kinematics with a central velocity at the innermost radii (0.″1 ≈ 34 pc) of 4860 km s<jats:sup>−1</jats:sup>. Both measurements differ significantly from the ∼4810 km s<jats:sup>−1</jats:sup> H<jats:sub>2</jats:sub>O megamaser velocity of the SMBH, supporting the prior indications of a velocity offset between the SMBH and its host galaxy. However, the two measurements also differ significantly from one another, and the galaxy as a whole exhibits a complex velocity structure that implies that the system has recently been dynamically disturbed. These results make it clear that the SMBH is not at rest with respect to the systemic velocity of the galaxy, though the specific nature of the mobile SMBH—i.e., whether it traces an ongoing galaxy merger, a binary black hole system, or a gravitational-wave recoil event—remains unclear.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Major flares and coronal mass ejections (CMEs) tend to originate from compact polarity inversion lines (PILs) in solar active regions (ARs). Recently, a scenario named “collisional shearing” was proposed by Chintzoglou et al. to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form a compact PIL, driving the shearing and flux cancellation that are responsible for the subsequent large activities. In this work, by tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of “collisional shearing.” We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, six from the conjoined systems of sPIL and cPIL, and two from the conjoined systems of sPIL and ePIL (external PIL between the AR and the nearby pre-existing polarities). Collision accompanied by shearing and flux cancellation is found to develop at all PILs prior to the eruptions, with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the more intense activities tend to originate from PILs with more severe collisions. The results suggest that “collisional shearing,” i.e., bipole–bipole interaction during the flux emergence, is a common process in driving the major activities in emerging ARs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We extend the halo-based group finder developed by Yang et al. (2005c) to use data <jats:italic>simultaneously</jats:italic> with either photometric or spectroscopic redshifts. A mock galaxy redshift survey constructed from a high-resolution <jats:italic>N</jats:italic>-body simulation is used to evaluate the performance of this extended group finder. For galaxies with magnitude z ≤ 21 and redshift 0 &lt; <jats:italic>z</jats:italic> ≤ 1.0 in the DESI legacy imaging surveys (the Legacy Surveys), our group finder successfully identifies more than 60% of the members in about 90% of halos with mass ≳10<jats:sup>12.5</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>. Detected groups with mass ≳10<jats:sup>12.0</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> have a purity (the fraction of true groups) greater than 90%. The halo mass assigned to each group has an uncertainty of about 0.2 dex at the high-mass end ≳10<jats:sup>13.5</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> and 0.45 dex at the low-mass end. Groups with more than 10 members have a redshift accuracy of ∼0.008. We apply this group finder to the Legacy Surveys DR8 and find 6.4 million groups with at least three members. About 500,000 of these groups have at least 10 members. The resulting catalog containing 3D coordinates, richness, halo masses, and total group luminosities is made publicly available.</jats:p>