Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The von Kármán-Howarth equations give a starting basis for the classical turbulence theory. The formula for the magnetohydrodynamics von Kármán decay rate represents an energy source in many solar wind models with turbulence as the driver. However, it still lacks the radial trend comparison between the von Kármán decay rate, the energy supply rate, and the perpendicular heating rate based on direct observations of the solar wind. Here we carry out this kind of comparison for the first time using Parker Solar Probe measurements from its first three orbits. We find that the radial variation of the von Kármán decay rate is consistent with that of both the energy supply rate and the heating rate in the slow solar wind. These results support the idea that the von Kármán decay law is an active process responsible for solar wind heating. These results also suggest a new idea that both the von Kármán decay law and the low-frequency break sweeping may be controlled by the same nonlinear process. Some limitations of the present study are also addressed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The chemical abundance patterns of gas and stars in galaxies are powerful probes of galaxies’ star formation histories and the astrophysics of galaxy assembly but are challenging to measure with confidence in distant galaxies. In this paper, we report the first measurements of the correlation between stellar mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) and multiple tracers of chemical enrichment (including O, N, and Fe) in individual <jats:italic>z</jats:italic> ∼ 2–3 galaxies, using a sample of 195 star-forming galaxies from the Keck Baryonic Structure Survey. The galaxies’ chemical abundances are inferred using photoionization models capable of reconciling high-redshift galaxies’ observed extreme rest-UV and rest-optical spectroscopic properties. We find that the <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>–O/H relation for our sample is relatively shallow, with moderately large scatter, and is offset ∼0.35 dex higher than the corresponding <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>–Fe/H relation. The two relations have very similar slopes, indicating a high level of <jats:italic>α</jats:italic>-enhancement—O/Fe ≈ 2.2 × (O/Fe)<jats:sub>⊙</jats:sub>—across two decades in <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>. The <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>–N/H relation has the steepest slope and largest intrinsic scatter, which likely results from the fact that many <jats:italic>z</jats:italic> ∼ 2 galaxies are observed near or past the transition from “primary” to “secondary” N production, and may reflect uncertainties in the astrophysical origin of N. Together, these results suggest that <jats:italic>z</jats:italic> ∼ 2 galaxies are old enough to have seen substantial enrichment from intermediate-mass stars, but are still young enough that Type Ia supernovae have not had time to contribute significantly to their enrichment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Galaxy evolution is driven by a variety of physical processes that are predicted to proceed at different rates for different dark matter haloes and environments across cosmic times. A record of this evolution is preserved in galaxy stellar populations, which we can access using absorption-line spectroscopy. Here we explore the large LEGA-C survey (DR3) to investigate the role of the environment and stellar mass on stellar populations at <jats:italic>z</jats:italic> ∼ 0.6–1 in the COSMOS field. Leveraging the statistical power and depth of LEGA-C, we reveal significant gradients in D<jats:sub> <jats:italic>n</jats:italic> </jats:sub>4000 and H<jats:italic>δ</jats:italic> equivalent widths (EWs) distributions over the stellar mass versus environment 2D spaces for the massive galaxy population (<jats:italic>M</jats:italic> &gt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) at <jats:italic>z</jats:italic> ∼ 0.6–1.0. D<jats:sub> <jats:italic>n</jats:italic> </jats:sub>4000 and H<jats:italic>δ</jats:italic> EWs primarily depend on stellar mass, but they also depend on environment at fixed stellar mass. By splitting the sample into centrals and satellites, and in terms of star-forming galaxies and quiescent galaxies, we reveal that the significant environmental trends of D<jats:sub> <jats:italic>n</jats:italic> </jats:sub>4000 and H<jats:italic>δ</jats:italic> EW, when controlling for stellar mass, are driven by quiescent galaxies. Regardless of being centrals or satellites, star-forming galaxies reveal D<jats:sub> <jats:italic>n</jats:italic> </jats:sub>4000 and H<jats:italic>δ</jats:italic> EWs, which depend strongly on their stellar mass and are completely independent of the environment at 0.6 &lt; <jats:italic>z</jats:italic> &lt; 1.0. The environmental trends seen for satellite galaxies are fully driven by the trends that hold only for quiescent galaxies, combined with the strong environmental dependency of the quiescent fraction at fixed stellar mass. Our results are consistent with recent predictions from simulations that point toward massive galaxies forming first in overdensities or the most compact dark matter haloes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We trained deep neural networks (DNNs) as a function of the neutrino energy density, flux, and the fluid velocity to reproduce the Eddington tensor for neutrinos obtained in our first-principles core-collapse supernova simulation. Although the moment method, which is one of the most popular approximations for neutrino transport, requires a closure relation, none of the analytical closure relations commonly employed in the literature capture all aspects of the neutrino angular distribution in momentum space. In this paper, we develop a closure relation by using DNNs that take the neutrino energy density, flux, and the fluid velocity as the inputs and the Eddington tensor as the output. We consider two kinds of DNNs: a conventional DNN, named a component-wise neural network (CWNN), and a tensor-basis neural network (TBNN). We find that the diagonal component of the Eddington tensor is better reproduced by the DNNs than the M1 closure relation, especially for low to intermediate energies. For the off-diagonal component, the DNNs agree better with the Boltzmann solver than the M1 closure relation at large radii. In the comparison between the two DNNs, the TBNN displays slightly better performance than the CWNN. With these new closure relations at hand, based on DNNs that well reproduce the Eddington tensor at much lower costs, we have opened up a new possibility for the moment method.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a numerical study, based on Monte Carlo simulations, aimed at defining new empirical parameters measurable from observations and able to trace the different phases of the dynamical evolution of star clusters. As expected, a central density cusp, deviating from the King model profile, develops during the core collapse (CC) event. Although the slope varies during the post-CC oscillations, the cusp remains a stable feature characterizing the central portion of the density profile in all post-CC stages. We then investigate the normalized cumulative radial distribution (nCRD) drawn by all the cluster stars included within one half of the tridimensional half-mass radius (<jats:italic>R</jats:italic> ≤ 0.5<jats:italic>r</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub>), finding that its morphology varies in time according to the cluster’s dynamical stage. To quantify these changes we defined three parameters: <jats:italic>A</jats:italic> <jats:sub>5</jats:sub>, the area subtended by the nCRD within 5% of the half-mass radius, <jats:italic>P</jats:italic> <jats:sub>5</jats:sub>, the value of the nCRD measured at the same distance, and <jats:italic>S</jats:italic> <jats:sub>2.5</jats:sub>, the slope of the straight line tangent to the nCRD measured at <jats:italic>R</jats:italic> = 2.5%<jats:italic>r</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub>. The three parameters evolve similarly during the cluster’s dynamical evolution: after an early phase in which they are essentially constant, their values rapidly increase, reaching their maximum at the CC epoch and slightly decreasing in the post-CC phase, when their average value remains significantly larger than the initial one, in spite of some fluctuations. The results presented in this paper suggest that these three observable parameters are very promising empirical tools to identify the star cluster’s dynamical stage from observational data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use 6 yr of data from the Dark Energy Survey to perform a detailed photometric characterization of the Phoenix stellar stream, a 15° long, thin, dynamically cold, low-metallicity stellar system in the Southern Hemisphere. We use natural splines, a nonparametric modeling technique, to simultaneously fit the stream track, width, and linear density. This updated stream model allows us to improve measurements of the heliocentric distance (17.4 ± 0.1 (stat.) ±0.8 (sys.) kpc) and distance gradient (−0.009 ± 0.006 kpc deg<jats:sup>−1</jats:sup>) of Phoenix, which corresponds to a small change of 0.13 ± 0.09 kpc in heliocentric distance along the length of the stream. We measure linear intensity variations on degree scales, as well as deviations in the stream track on ∼2° scales, suggesting that the stream may have been disturbed during its formation and/or evolution. We recover three peaks and one gap in linear intensity along with fluctuations in the stream track. Compared to other thin streams, the Phoenix stream shows more fluctuations and, consequently, the study of Phoenix offers a unique perspective on gravitational perturbations of stellar streams. We discuss possible sources of perturbations to Phoenix, including baryonic structures in the Galaxy and dark matter subhalos.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use an updated version of the halo-based galaxy group catalog of Yang et al., and take the surface brightness of the galaxy group (<jats:italic>μ</jats:italic> <jats:sub>lim</jats:sub>) based on projected positions and luminosities of galaxy members as a compactness proxy to divide groups into subsystems with different compactness. By comparing various properties, including galaxy conditional luminosity function, stellar population, active galactic nuclei (AGN) activity, and X-ray luminosity of the intracluster medium of carefully controlled high (HC) and low compactness (LC) group samples, we find that group compactness plays an essential role in characterizing the detailed physical properties of the group themselves and their group members, especially for low-mass groups with <jats:italic>M</jats:italic> <jats:sub>h</jats:sub> ≲ 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>. We find that the low-mass HC groups have a systematically lower magnitude gap Δ<jats:italic>m</jats:italic> <jats:sub>12</jats:sub> and X-ray luminosity than their LC counterparts, indicating that the HC groups are probably in the early stage of group merging. On the other hand, a higher fraction of passive galaxies is found in the HC group, which however is a result of systematically smaller halo-centric distance distribution of their satellite population. After controlling for both <jats:italic>M</jats:italic> <jats:sub>h</jats:sub> and halo-centric distance, we did not find any differences in both the quenching fraction and AGN activity of the member galaxies between the HC and LC groups. Therefore, we conclude that the halo quenching effect, which results in the halo-centric dependence of a galaxy population, is a faster process compared to the dynamical relaxed timescale of galaxy groups.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The groundbreaking image of the black hole at the center of the M87 galaxy has raised questions at the intersection of observational astronomy and black hole physics. How well can the radius of a black hole shadow be measured, and can this measurement be used to distinguish general relativity from other theories of gravity? We explore these questions using a simple spherical flow model in general relativity, scalar Gauss–Bonnet gravity, and the Rezzolla and Zhidenko parameterized metric. We assume an optically thin plasma with power-law emissivity in radius. Along the way we present a generalized Bondi flow, as well as a piecewise analytic model for the brightness profile of a cold inflow. We use the second moment of a synthetic image as a proxy for EHT observables and compute the ratio of the second moment to the radius of the black hole shadow. We show that corrections to this ratio from modifications to general relativity are subdominant compared to corrections to the critical impact parameter, and we argue that this is generally true. In our simplified model the astrophysical parameter uncertainty dominates the gravity theory parameter uncertainty, underlining the importance of understanding the accretion model if EHT is to be used to successfully test theories of gravity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Kepler and Transiting Exoplanet Survey Satellite (TESS) missions have generated over 100,000 potential transit signals that must be processed in order to create a catalog of planet candidates. During the past few years, there has been a growing interest in using machine learning to analyze these data in search of new exoplanets. Different from the existing machine learning works, <jats:monospace>ExoMiner</jats:monospace>, the proposed deep learning classifier in this work, mimics how domain experts examine diagnostic tests to vet a transit signal. <jats:monospace>ExoMiner</jats:monospace> is a highly accurate, explainable, and robust classifier that (1) allows us to validate 301 new exoplanets from the MAST Kepler Archive and (2) is general enough to be applied across missions such as the ongoing TESS mission. We perform an extensive experimental study to verify that <jats:monospace>ExoMiner</jats:monospace> is more reliable and accurate than the existing transit signal classifiers in terms of different classification and ranking metrics. For example, for a fixed precision value of 99%, <jats:monospace>ExoMiner</jats:monospace> retrieves 93.6% of all exoplanets in the test set (i.e., recall = 0.936), while this rate is 76.3% for the best existing classifier. Furthermore, the modular design of <jats:monospace>ExoMiner</jats:monospace> favors its explainability. We introduce a simple explainability framework that provides experts with feedback on why <jats:monospace>ExoMiner</jats:monospace> classifies a transit signal into a specific class label (e.g., planet candidate or not planet candidate).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Blazars show extreme observational properties that are due to the beaming effect with the jet being close to the line of sight. It was found that the observed luminosity is anticorrelated with the synchrotron peak frequency but the debeamed luminosity and the frequency is positively correlated. In this work, we revisit this correlation for a large sample of 255 blazars from the fourth Fermi catalog with available Doppler factors. Our analysis comes to the following conclusions. (1) The observed radio, X-ray, <jats:italic>γ</jats:italic>-ray, and synchrotron peak luminosity are all anticorrelated with the peak frequency, but the debeamed luminosity is positively correlated with the debeamed peak frequency. The anticorrelation is due to a selection effect or a beaming effect. (2) The Compton dominance parameter is correlated with both the bolometric luminosity and Doppler factor, implying that the more highly Compton-dominated sources are more luminous. (3) The bolometric luminosity can be represented by the <jats:italic>γ</jats:italic>-ray luminosity for Fermi blazars.</jats:p>