Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The Voit et al. black hole feedback valve model predicts relationships between stellar velocity dispersion and atmospheric structure among massive early-type galaxies. In this work, we test that model using the Chandra archival sample of 49 early-type galaxies from Lakhchaura et al. We consider relationships between stellar velocity dispersion and entropy profile slope, multiphase gas extent, and the ratio of cooling time to freefall time. We also define subsamples based on data quality and entropy profile properties that clarify those relationships and enable more specific tests of the model predictions. We find that the atmospheric properties of early-type galaxies generally align with the predictions of the Voit et al. model, in that galaxies with a greater stellar velocity dispersion tend to have radial profiles of pressure, gas density, and entropy with steeper slopes and less extended multiphase gas. Quantitative agreement with the model predictions improves when the sample is restricted to have low central entropy and a stellar velocity dispersion of between 220 and 300 km s<jats:sup>−1</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Kelvin–Helmholtz instability (KHI) can be generated at velocity shears in plasmas. While shears are abundant in the solar wind, whether they generate KHI in situ remains an open question, because of the lack of models that can simultaneously resolve the global structure of the expanding solar wind and the local structure of much smaller-scale velocity shears. In this paper, we use the Grid Agnostic MHD for Extended Research Applications model whose high resolving power, in combination with a highly refined spatial grid, allowed us to extend the simulation from global scales roughly into the first decade of the inertial range (∼1.5 × 10<jats:sup>5</jats:sup> km, which we refer to as mesoscale). We employ this computational capability to extract from the simulation the local properties of radial and azimuthal solar wind velocity shears and investigate their KH stability using a linear dispersion relation, which includes both the finite width of the shear and plasma compressibility. We find that radial shears, which dominate the global structure of the inner heliosphere, are stabilized by compressibility. However, depending on the local Alfvén speed, sound speed, shear thickness, and the strength of the stabilizing azimuthal magnetic field, the azimuthal shears generated inside stream interaction regions could be KH-unstable. While our highly resolved simulation allowed us to analyze the local properties of the velocity shears, its resolution was still insufficient to confirm the instability. We argue that even higher resolution simulations are required to reproduce in situ generation of KHI at velocity shears in the solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the effects of anisotropic thermal conduction, anisotropic pressure, and magnetic field strength on the hot accretion flows around black holes by solving the axisymmetric, steady-state magnetohydrodynamic equations. The anisotropic pressure is known as a mechanism for transporting angular momentum in weakly collisional plasmas in hot accretion flows with extremely low mass accretion rates. However, anisotropic pressure does not extensively impact the transport of the angular momentum, it leads to shrinkage of the wind region. Our results show that the strength of the magnetic field can help the Poynting energy flux overcome the kinetic energy flux. This result may be applicable to the understanding of the hot accretion flow in the Galactic Center Sgr A* and the M87 galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Motivated by the detection of very-high-energy (VHE) gamma rays deep in the afterglow emission of a gamma-ray burst (GRB), we revisit predictions of the maximum energy to which electrons can be accelerated at a relativistic blast wave. Acceleration at the weakly magnetized forward shock of a blast wave can be limited by either the rapid damping of turbulence generated behind the shock, the effect of a large-scale ambient magnetic field, or radiation losses. Within the confines of a standard, single-zone, synchrotron self-Compton (SSC) model, we show that observations of GRB 190829A rule out a rapid damping of the downstream turbulence. Furthermore, simultaneous fits to the X-ray and TeV gamma-ray emission of this object are not possible unless the limit on acceleration imposed by the ambient magnetic field is comparable to or weaker than that imposed by radiation losses. This requires the dominant length scale of the turbulence behind the shock to be larger than that implied by particle-in-cell simulations. However, even then, Klein–Nishina effects prevent production of the hard VHE gamma-ray spectrum suggested by observations. Thus, TeV observations of GRB afterglows, though still very sparse, are already in tension with the SSC emission scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations indicate that turbulence in the interstellar medium (ISM) is supersonic (<jats:italic>M</jats:italic> <jats:sub>turb</jats:sub> ≫ 1) and strongly magnetized (<jats:italic>β</jats:italic> ∼ 0.01–1), while in the intracluster medium (ICM) it is subsonic (<jats:italic>M</jats:italic> <jats:sub>turb</jats:sub> ≲ 1) and weakly magnetized (<jats:italic>β</jats:italic> ∼ 100). Here, <jats:italic>M</jats:italic> <jats:sub>turb</jats:sub> is the turbulent Mach number and <jats:italic>β</jats:italic> is the plasma beta. We study the properties of shocks induced in these disparate environments, including the distribution of the shock Mach number, <jats:italic>M</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>, and the dissipation of the turbulent energy at shocks, through numerical simulations using a high-order, accurate code based on the weighted essentially nonoscillatory scheme. In particular, we investigate the effects of different modes of the forcing that drives turbulence: solenoidal, compressive, and a mixture of the two. In ISM turbulence, while the density distribution looks different with different forcings, the velocity power spectrum, <jats:italic>P</jats:italic> <jats:sub> <jats:italic>v</jats:italic> </jats:sub>, on small scales exhibits only weak dependence. Hence, the statistics of shocks depend weakly on forcing either. In the ISM models with <jats:italic>M</jats:italic> <jats:sub>turb</jats:sub> ≈ 10 and <jats:italic>β</jats:italic> ∼ 0.1, the fraction of the turbulent energy dissipated at shocks is estimated to be ∼15%, not sensitive to the forcing mode. In contrast, in ICM turbulence, <jats:italic>P</jats:italic> <jats:sub> <jats:italic>v</jats:italic> </jats:sub> as well as the density distribution show strong dependence on forcing. The frequency and average Mach number of shocks are greater for compressive forcing than for solenoidal forcing; so is the energy dissipation. The fraction of the ensuing shock dissipation is in the range of ∼10%–35% in the ICM models with <jats:italic>M</jats:italic> <jats:sub>turb</jats:sub> ≈ 0.5 and <jats:italic>β</jats:italic> ∼ 10<jats:sup>6</jats:sup>. The rest of the turbulent energy should be dissipated through turbulent cascade.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Any viable cosmological framework has to match the observed proportion of early- and late-type galaxies. In this contribution, we focus on the distribution of galaxy morphological types in the standard model of cosmology (Lambda cold dark matter, ΛCDM). Using the latest state-of-the-art cosmological ΛCDM simulations known as Illustris, IllustrisTNG, and EAGLE, we calculate the intrinsic and sky-projected aspect ratio distribution of the stars in subhalos with stellar mass <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> &gt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at redshift <jats:italic>z</jats:italic> = 0. There is a significant deficit of intrinsically thin disk galaxies, which however comprise most of the locally observed galaxy population. Consequently, the sky-projected aspect ratio distribution produced by these ΛCDM simulations disagrees with the Galaxy And Mass Assembly (GAMA) survey and Sloan Digital Sky Survey at ≥12.52<jats:italic>σ</jats:italic> (TNG50-1) and ≥14.82<jats:italic>σ</jats:italic> (EAGLE50) confidence. The deficit of intrinsically thin galaxies could be due to a much less hierarchical merger-driven build-up of observed galaxies than is given by the ΛCDM framework. It might also arise from the implemented sub-grid models, or from the limited resolution of the above-mentioned hydrodynamical simulations. We estimate that an 8<jats:sup>5</jats:sup> times better mass resolution realization than TNG50-1 would reduce the tension with GAMA to the 5.58<jats:italic>σ</jats:italic> level. Finally, we show that galaxies with fewer major mergers have a somewhat thinner aspect ratio distribution. Given also the high expected frequency of minor mergers in ΛCDM, the problem may be due to minor mergers. In this case, the angular momentum problem could be alleviated in Milgromian dynamics because of a reduced merger frequency arising from the absence of dynamical friction between extended dark matter halos.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>“Changing-look” active galactic nuclei (CL-AGNs) are a newly discovered class of AGNs that show the appearance (or disappearance) of broad emission lines within short timescales (months to years), and are often associated with dramatic changes in their continuum emissions. They provide us with an unprecedented chance to directly investigate the host galaxy properties with minimal contamination from the luminous central engine during the turn-off state, which is difficult for normal luminous AGNs. In this work, for the first time, we systematically characterize the stellar populations and star formation histories of host galaxies for 26 turn-off CL-AGNs using the stellar population synthesis code STARLIGHT. We find that the stellar populations of CL-AGNs are similar to those of normal AGNs, except that the intermediate stellar populations contribute more fractions. We estimate their stellar velocity dispersions (<jats:italic>σ</jats:italic> <jats:sub>⋆</jats:sub>) and black hole masses (<jats:italic>M</jats:italic> <jats:sub>BH,vir</jats:sub>), and find that CL-AGNs also follow the overall <jats:italic>M</jats:italic> <jats:sub>BH</jats:sub>–<jats:italic>σ</jats:italic> <jats:sub>⋆</jats:sub> relationship. We also confirm the previous claims that CL-AGNs tend to be biased toward lower Eddington ratios, and that their extreme variabilities are more likely due to the intrinsic changes of the accretion rates. In addition, CL-AGNs with recent star formations tend to have higher Eddington ratios. Compared with previous studies, our analysis suggests that there may be a correlation between CL-AGN host galaxy properties and their CL phenomena.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV <jats:italic>γ</jats:italic>-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to ∼100 GeV) and the Fermi Large Area Telescope to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and current-sheet model, invoking a step function for the accelerating electric field as motivated by kinetic simulations. We include a refined calculation of the curvature radius of particle trajectories in the lab frame, impacting the particle transport, predicted light curves, and spectra. Our model reproduces the decrease of the flux of the first peak relative to the second one, evolution of the bridge emission, near-constant phase positions of peaks, and narrowing of pulses with increasing energy. We can explain the first of these trends because we find that the curvature radii of the particle trajectories in regions where the second <jats:italic>γ</jats:italic>-ray light-curve peak originates are systematically larger than those associated with the first peak, implying that the spectral cutoff of the second peak is correspondingly larger. However, an unknown azimuthal dependence of the <jats:italic>E</jats:italic> field, as well as uncertainty in the precise spatial origin of the GeV emission, precludes a simplistic discrimination of emission mechanisms.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent in situ observations from the Parker Solar Probe (PSP) mission in the inner heliosphere near perihelia show evidence of ion beams, temperature anisotropies, and kinetic wave activity, which are likely associated with kinetic heating and acceleration processes of the solar wind. In particular, the proton beams were detected by PSP/Solar Probe Analyzers-Ion (SPAN-I) and related magnetic fluctuation spectra associated with ion-scale waves were observed by the FIELDS instrument. We present the ion velocity distribution functions (VDFs) from SPAN-I and the results of 2.5D and 3D hybrid-particle-in-cell models of proton and <jats:italic>α</jats:italic> particle super-Alfvénic beams that drive ion kinetic instabilities and waves in the inner heliospheric solar wind. We model the evolution of the ion VDFs with beams, and obtain the ion relative drifts speeds, and ion temperature anisotropies for solar wind conditions near PSP perihelia. We calculate the partition of energies between the particles (ions) along and perpendicular and parallel to the magnetic field, as well as the evolution of magnetic energy, and compare to observationally deduced values. We conclude that the ion beam driven kinetic instabilities in the solar wind plasma near perihelia are important components in the cascade of energy from fluid to kinetic scales, an important component in the solar wind plasma heating process.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We derive solutions to transit light curves of exoplanets orbiting rapidly rotating stars. These stars exhibit significant oblateness and gravity darkening, a phenomenon where the poles of the star have a higher temperature and luminosity than the equator. Light curves for exoplanets transiting these stars can exhibit deviations from those of slowly rotating stars, even displaying significantly asymmetric transits depending on the system’s spin–orbit angle. As such, these phenomena can be used as a protractor to measure the spin–orbit alignment of the system. In this paper, we introduce a novel semianalytic method for generating model light curves for gravity-darkened and oblate stars with transiting exoplanets. We implement the model within the code package <jats:sans-serif>starry </jats:sans-serif>and demonstrate several orders of magnitude improvement in speed and precision over existing methods. We test the model on a TESS light curve of WASP-33, whose host star displays rapid rotation (<jats:inline-formula> <jats:tex-math> <?CDATA $v\sin {i}_{* }=86.4$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:msub> <mml:mrow> <mml:mi>i</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>86.4</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac33aaieqn1.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>). We subtract the host’s <jats:italic>δ</jats:italic>-Scuti pulsations from the light curve, finding an asymmetric transit characteristic of gravity darkening. We find the projected spin–orbit angle is consistent with Doppler tomography and constrain the true spin–orbit angle of the system as <jats:inline-formula> <jats:tex-math> <?CDATA $\varphi ={108.3}_{-15.4}^{+19.0}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>φ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>108.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>15.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>19.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac33aaieqn2.gif" xlink:type="simple" /> </jats:inline-formula>°. We demonstrate the method’s uses in constraining spin–orbit inclinations of such systems photometrically with posterior inference. Lastly, we note the use of such a method for inferring the dynamical history of thousands of such systems discovered by TESS (<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://github.com/rodluger/starry" xlink:type="simple">https://github.com/rodluger/starry</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://rodluger.github.io/starry" xlink:type="simple">https://rodluger.github.io/starry</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://github.com/shashankdholakia/gravity-dark" xlink:type="simple">https://github.com/shashankdholakia/gravity-dark</jats:ext-link>).</jats:p>