Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>As the fundamental physical process with many astrophysical implications, the diffusion of cosmic rays (CRs) is determined by their interaction with magnetohydrodynamic (MHD) turbulence. We consider the magnetic mirroring effect arising from MHD turbulence on the diffusion of CRs. Due to the intrinsic superdiffusion of turbulent magnetic fields, CRs with large pitch angles that undergo mirror reflection, i.e., bouncing CRs, are not trapped between magnetic mirrors, but move diffusively along the turbulent magnetic field, leading to a new type of parallel diffusion, i.e., mirror diffusion. This mirror diffusion is in general slower than the diffusion of nonbouncing CRs with small pitch angles that undergo gyroresonant scattering. The critical pitch angle at the balance between magnetic mirroring and pitch-angle scattering is important for determining the diffusion coefficients of both bouncing and nonbouncing CRs and their scalings with the CR energy. We find nonuniversal energy scalings of diffusion coefficients, depending on the properties of MHD turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present and analyze ALMA submillimeter observations from a multiwavelength campaign of Sgr A* during 2019 July 18. In addition to the submillimeter, we utilize concurrent mid-infrared (mid-IR; Spitzer) and X-ray (Chandra) observations. The submillimeter emission lags less than <jats:italic>δ</jats:italic> <jats:italic>t</jats:italic> ≈ 30 minutes behind the mid-IR data. However, the entire submillimeter flare was not observed, raising the possibility that the time delay is a consequence of incomplete sampling of the light curve. The decay of the submillimeter emission is not consistent with synchrotron cooling. Therefore, we analyze these data adopting an adiabatically expanding synchrotron source that is initially optically thick or thin in the submillimeter, yielding time-delayed or synchronous flaring with the IR, respectively. The time-delayed model is consistent with a plasma blob of radius 0.8 <jats:italic>R</jats:italic> <jats:sub>S</jats:sub> (Schwarzschild radius), electron power-law index <jats:italic>p</jats:italic> = 3.5 (<jats:italic>N</jats:italic>(<jats:italic>E</jats:italic>) ∝ <jats:italic>E</jats:italic> <jats:sup>−<jats:italic>p</jats:italic> </jats:sup>), equipartition magnetic field of <jats:italic>B</jats:italic> <jats:sub>eq</jats:sub> ≈ 90 Gauss, and expansion velocity <jats:inline-formula> <jats:tex-math> <?CDATA ${v}_{\exp }\approx 0.004c$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>exp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.004</mml:mn> <mml:mi>c</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2d2cieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The simultaneous emission is fit by a plasma blob of radius 2 <jats:italic>R</jats:italic> <jats:sub>S</jats:sub>, <jats:italic>p</jats:italic> = 2.5, <jats:italic>B</jats:italic> <jats:sub>eq</jats:sub> ≈ 27 Gauss, and <jats:inline-formula> <jats:tex-math> <?CDATA ${v}_{\exp }\approx 0.014c$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>exp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.014</mml:mn> <mml:mi>c</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2d2cieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Since the submillimeter time delay is not completely unambiguous, we cannot definitively conclude which model better represents the data. This observation presents the best evidence for a unified flaring mechanism between submillimeter and X-ray wavelengths and places significant constraints on the source size and magnetic field strength. We show that concurrent observations at lower frequencies would be able to determine if the flaring emission is initially optically thick or thin in the submillimeter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We simulate the influence of the energy that the merger process of two neutron stars (NSs) releases inside a red supergiant (RSG) star on the RSG envelope inner to the merger location. In the triple-star common envelope evolution (CEE) that we consider, a tight binary system of two NSs spiraling in inside an RSG envelope and because of mass accretion and dynamical friction, the two NSs merge. We deposit merger-explosion energies of 3 × 10<jats:sup>50</jats:sup> and 10<jats:sup>51</jats:sup> erg at distances of 25 and 50 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> from the center of the RSG, and with the three-dimensional hydrodynamical code FLASH we follow the evolution of the RSG envelope in inner regions. For the parameters we explore, we find that more than 90% of the RSG envelope mass inward of the merger site stays bound to the RSG. NSs that experience CEE are likely to accrete RSG envelope mass through an accretion disk that launches jets. These jets power a luminous transient event, a common envelope jets supernova (CEJSN). The merger process adds to the CEJSN energy. Our finding implies that the interaction of the merger product, a massive NS or a BH, with the envelope can continue to release more energy, both by further inspiraling and by mass accretion by the merger product. Massive RSG envelopes can force the merger product to spiral into the core of the RSG, leading to an even more energetic CEJSN.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The circumgalactic medium (CGM) contains information on gas flows around galaxies, such as accretion and supernova-driven winds, which are difficult to constrain from observations alone. Here, we use the high-resolution TNG50 cosmological magnetohydrodynamical simulation to study the properties and kinematics of the CGM around star-forming galaxies in 10<jats:sup>11.5</jats:sup>–10<jats:sup>12</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> halos at <jats:italic>z</jats:italic> ≃ 1 using mock Mg <jats:sc>ii</jats:sc> absorption lines, which we generate by postprocessing halos to account for photoionization in the presence of a UV background. We find that the Mg <jats:sc>ii</jats:sc> gas is a very good tracer of the cold CGM, which is accreting inward at inflow velocities of up to 50 km s<jats:sup>−1</jats:sup>. For sight lines aligned with the galaxy’s major axis, we find that Mg <jats:sc>ii</jats:sc> absorption lines are kinematically shifted due to the cold CGM’s significant corotation at speeds up to 50% of the virial velocity for impact parameters up to 60 kpc. We compare mock Mg <jats:sc>ii</jats:sc> spectra to observations from the MusE GAs FLow and Wind (MEGAFLOW) survey of strong Mg <jats:sc>ii</jats:sc> absorbers (EW<jats:sup>2796 Å</jats:sup> <jats:sub>0</jats:sub> &gt; 0.5 Å). After matching the equivalent-width (EW) selection, we find that the mock Mg <jats:sc>ii</jats:sc> spectra reflect the diversity of observed kinematics and EWs from MEGAFLOW, even though the sight lines probe a very small fraction of the CGM. Mg <jats:sc>ii</jats:sc> absorption in higher-mass halos is stronger and broader than in lower-mass halos but has qualitatively similar kinematics. The median-specific angular momentum of the Mg <jats:sc>ii</jats:sc> CGM gas in TNG50 is very similar to that of the entire CGM and only differs from non-CGM components of the halo by normalization factors of ≲1 dex.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Given a known radial magnetic field distribution on the Sun’s photospheric surface, there exist well-established methods for computing a potential magnetic field in the corona above. Such potential fields are routinely used as input to solar wind models, and to initialize magneto-frictional or full magnetohydrodynamic simulations of the coronal and heliospheric magnetic fields. We describe an improved magnetic field model that calculates a magneto-frictional equilibrium with an imposed solar wind profile (which can be Parker’s solar wind solution, or any reasonable equivalent). These “outflow fields” appear to approximate the real coronal magnetic field more closely than a potential field, take a similar time to compute, and avoid the need to impose an artificial source surface. Thus they provide a practical alternative to the potential field model for initializing time-evolving simulations or modeling the heliospheric magnetic field. We give an open-source Python implementation in spherical coordinates and apply the model to data from solar cycle 24. The outflow tends to increase the open magnetic flux compared to the potential field model, reducing the well-known discrepancy with in situ observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a simple, unified model that can explain two of the brightest, large-scale, diffuse, polarized radio features in the sky, the North Polar Spur (NPS) and the Fan Region, along with several other prominent loops. We suggest that they are long, magnetized, and parallel filamentary structures that surround the Local arm and/or Local Bubble, in which the Sun is embedded. We show that this model is consistent with the large number of observational studies on these regions and is able to resolve an apparent contradiction in the literature that suggests that the high-latitude portion of the NPS is nearby, while lower-latitude portions are more distant. Understanding the contributions of this local emission is critical to developing a complete model of the Galactic magnetic field. These very nearby structures also provide context to help understand similar nonthermal, filamentary structures that are increasingly being observed with modern radio telescopes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of six radio-loud quasar host galaxies at <jats:italic>z</jats:italic> = 1.4–2.3. We combine the kiloparsec-scale resolution ALMA observations with high spatial resolution adaptive optics integral field spectrograph data of the ionized gas. We detect molecular gas emission in five quasar host galaxies and resolve the molecular interstellar medium using the CO (3–2) or CO (4–3) rotational transitions. Clumpy molecular outflows are detected in four quasar host galaxies and a merger system 21 kpc away from one quasar. Between the ionized and cold molecular gas phases, the majority of the outflowing mass is in a molecular phase, while for three out of four detected multiphase gas outflows, the majority of the kinetic luminosity and momentum flux is in the ionized phase. Combining the energetics of the multiphase outflows, we find that their driving mechanism is consistent with energy-conserving shocks produced by the impact of the quasar jets with the gas in the galaxy. By assessing the molecular gas mass to the dynamics of the outflows, we estimate a molecular gas depletion timescale of a few megayears. The gas outflow rates exceed the star formation rates, suggesting that quasar feedback is a major mechanism of gas depletion at the present time. The coupling efficiency between the kinetic luminosity of the outflows and the bolometric luminosity of the quasar of 0.1%–1% is consistent with theoretical predictions. Studying multiphase gas outflows at high redshift is important for quantifying the impact of negative feedback in shaping the evolution of massive galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We measure the star formation rate (SFR) per unit gas mass and the star formation efficiency (SFE<jats:sub>gas</jats:sub> for total gas, SFE<jats:sub>mol</jats:sub> for the molecular gas) in 81 nearby galaxies selected from the EDGE-CALIFA survey, using <jats:sup>12</jats:sup>CO (<jats:italic>J</jats:italic> = 1–0) and optical IFU data. For this analysis we stack CO spectra coherently by using the velocities of H<jats:italic>α</jats:italic> detections to detect fainter CO emission out to galactocentric radii <jats:italic>r</jats:italic> <jats:sub>gal</jats:sub> ∼ 1.2<jats:italic>r</jats:italic> <jats:sub>25</jats:sub> (∼3<jats:italic>R</jats:italic> <jats:sub>e</jats:sub>) and include the effects of metallicity and high surface densities in the CO-to-H<jats:sub>2</jats:sub> conversion. We determine the scale lengths for the molecular and stellar components, finding a close to 1:1 relation between them. This result indicates that CO emission and star formation activity are closely related. We examine the radial dependence of SFE<jats:sub>gas</jats:sub> on physical parameters such as galactocentric radius, stellar surface density Σ<jats:sub>⋆</jats:sub>, dynamical equilibrium pressure <jats:italic>P</jats:italic> <jats:sub>DE</jats:sub>, orbital timescale <jats:italic>τ</jats:italic> <jats:sub>orb</jats:sub>, and the Toomre <jats:italic>Q</jats:italic> stability parameter (including star and gas <jats:italic>Q</jats:italic> <jats:sub>star+gas</jats:sub>). We observe a generally smooth, continuous exponential decline in the SFE<jats:sub>gas</jats:sub> with <jats:italic>r</jats:italic> <jats:sub>gal</jats:sub>. The SFE<jats:sub>gas</jats:sub> dependence on most of the physical quantities appears to be well described by a power law. Our results also show a flattening in the SFE<jats:sub>gas</jats:sub>–<jats:italic>τ</jats:italic> <jats:sub>orb</jats:sub> relation at <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}[{\tau }_{\mathrm{orb}}]\sim 7.9\mbox{--}8.1$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">[</mml:mo> <mml:msub> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>orb</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">]</mml:mo> <mml:mo>∼</mml:mo> <mml:mn>7.9</mml:mn> <mml:mo>–</mml:mo> <mml:mn>8.1</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2b29ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and a morphological dependence of the SFE<jats:sub>gas</jats:sub> per orbital time, which may reflect star formation quenching due to the presence of a bulge component. We do not find a clear correlation between SFE<jats:sub>gas</jats:sub> and <jats:italic>Q</jats:italic> <jats:sub>star+gas</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The synchrotron spectrum of radio knot C in the protostellar object DG Tau has a low-frequency turnover. This is used to show that its magnetic field strength is likely to be at least 10 mG, which is roughly two orders of magnitude larger than previously estimated. The earlier, lower value is due to an overestimate of the emission volume together with an omission of the dependence of the minimum magnetic field on the synchrotron spectral index. Since the source is partially resolved, this implies a low volume-filling factor for the synchrotron emission. It is argued that the high pressure needed to account for the observations is due to shocks. In addition, cooling of the thermal gas is probably necessary in order to further enhance the magnetic field strength as well as the density of relativistic electrons. It is suggested that the observed spectral index implies that the energy of the radio-emitting electrons is below that needed to take part in first-order Fermi acceleration. Hence, the radio emission gives insights to the properties of its pre-acceleration phase. Attention is also drawn to the similarities between the properties of radio knot C and the shock-induced radio emission in supernovae.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The advent of high-resolution spectroscopy (<jats:italic>R</jats:italic> ≳ 25,000) as a method for characterization of exoplanet atmospheres has expanded our capability to study nontransiting planets, vastly increasing the number of planets accessible for observation. Many of the most favorable targets for atmospheric characterization are hot Jupiters, where we expect large spatial variation in physical conditions such as temperature, wind speed, and cloud coverage, making viewing geometry important. Three-dimensional models have generally simulated observational properties of hot Jupiters assuming edge-on viewing, which can be compared to observations of transiting planets, but neglected the large fraction of planets without nearly edge-on orbits. As the first investigation of how orbital inclination manifests in high-resolution emission spectra from three-dimensional models, we use a general circulation model to simulate the atmospheric structure of Upsilon Andromedae b, a typical nontransiting hot Jupiter with high observational interest, due the brightness of its host star. We compare models with and without clouds, and find that cloud coverage intensifies spatial variations by making colder regions dimmer and relatedly enhancing emission from the clear, hotter regions. This increases both the net Doppler shifts and the variation of the continuum flux amplitude over the course of the planet’s orbit. In order to accurately capture scattering from clouds, we implement a generalized two-stream radiative transfer routine for inhomogeneous multiple scattering atmospheres. As orbital inclination decreases, four key features of the high-resolution emission spectra also decrease in both the clear and cloudy models: (1) the average continuum flux level, (2) the amplitude of the variation in continuum with orbital phase, (3) net Doppler shifts of spectral lines, and (4) Doppler broadening in the spectra. Models capable of treating inhomogeneous cloud coverage and different viewing geometries are critical in understanding results from high-resolution emission spectra, enabling an additional avenue to investigate these extreme atmospheres.</jats:p>