Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Signatures of vertical disequilibrium have been observed across the Milky Way’s (MW’s) disk. These signatures manifest locally as unmixed phase spirals in <jats:italic>z</jats:italic>–<jats:italic>v</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub> space (“snails-in-phase”), and globally as nonzero mean <jats:italic>z</jats:italic> and <jats:italic>v</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub>, wrapping around the disk into physical spirals in the <jats:italic>x</jats:italic>–<jats:italic>y</jats:italic> plane (“snails-in-space”). We explore the connection between these local and global spirals through the example of a satellite perturbing a test-particle MW-like disk. We anticipate our results to broadly apply to any vertical perturbation. Using a <jats:italic>z</jats:italic>–<jats:italic>v</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub> asymmetry metric, we demonstrate that in test-particle simulations: (a) multiple local phase-spiral morphologies appear when stars are binned by azimuthal action <jats:italic>J</jats:italic> <jats:sub> <jats:italic>ϕ</jats:italic> </jats:sub>, excited by a single event (in our case, a satellite disk crossing); (b) these distinct phase spirals are traced back to distinct disk locations; and (c) they are excited at distinct times. Thus, local phase spirals offer a global view of the MW’s perturbation history from multiple perspectives. Using a toy model for a Sagittarius (Sgr)–like satellite crossing the disk, we show that the full interaction takes place on timescales comparable to orbital periods of disk stars within <jats:italic>R</jats:italic> ≲ 10 kpc. Hence such perturbations have widespread influence, which peaks in distinct regions of the disk at different times. This leads us to examine the ongoing MW–Sgr interaction. While Sgr has not yet crossed the disk (currently, <jats:italic>z</jats:italic> <jats:sub>Sgr</jats:sub> ≈ −6 kpc, <jats:italic>v</jats:italic> <jats:sub> <jats:italic>z</jats:italic>,Sgr</jats:sub> ≈ 210 km s<jats:sup>−1</jats:sup>), we demonstrate that the peak of the impact has already passed. Sgr’s pull over the past 150 Myr creates a global <jats:italic>v</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub> signature with amplitude ∝ <jats:italic>M</jats:italic> <jats:sub>Sgr</jats:sub>, which might be detectable in future spectroscopic surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present deep and high-fidelity images of the merging galaxy cluster A2256 at low frequencies using the upgraded Giant Metrewave Radio Telescope (uGMRT) and LOw-Frequency ARray (LOFAR). This cluster hosts one of the most prominent known relics with a remarkably spectacular network of filamentary substructures. The new uGMRT (300–850 MHz) and LOFAR (120–169 MHz) observations, combined with the archival Karl G. Jansky Very Large Array (VLA; 1–4 GHz) data, allowed us to carry out the first spatially resolved spectral analysis of the exceptional relic emission down to 6″ resolution over a broad range of frequencies. Our new sensitive radio images confirm the presence of complex filaments of magnetized relativistic plasma also at low frequencies. We find that the integrated spectrum of the relic is consistent with a single power law, without any sign of spectral steepening, at least below 3 GHz. Unlike previous claims, the relic shows an integrated spectral index of −1.07 ± 0.02 between 144 MHz and 3 GHz, which is consistent with the (quasi)stationary shock approximation. The spatially resolved spectral analysis suggests that the relic surface very likely traces the complex shock front, with a broad distribution of Mach numbers propagating through a turbulent and dynamically active intracluster medium. Our results show that the northern part of the relic is seen edge-on and the southern part close to face-on. We suggest that the complex filaments are regions where higher Mach numbers dominate the (re)acceleration of electrons that are responsible for the observed radio emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Mass accretion from the circumstellar disk onto the protostar is a fundamental process during star formation. Measuring the mass accretion rate is particularly challenging for stars belonging to binary systems, because it is often difficult to discriminate which component is accreting. DQ Tau is an almost equal-mass spectroscopic binary system where the components orbit each other every 15.8 days. The system is known to display pulsed accretion, i.e., the periodic modulation of the accretion by the components on eccentric orbit. We present multi-epoch ESO/Very Large Telescope X-Shooter observations of DQ Tau, with the aim of determining which component of this system is the main accreting source. We use the absorption lines in the spectra to determine the radial velocity of the two components, and measure the continuum veiling as a function of wavelength and time. We fit the observed spectra with nonaccreting templates to correct for the photospheric and chromospheric contribution. In the corrected spectra, we study in detail the profiles of the emission lines and calculate mass accretion rates for the system as a function of orbital phase. In accordance with previous findings, we detect elevated accretion close to periastron. We measure the accretion rate as varying between 10<jats:sup>−8.5</jats:sup> and 10<jats:sup>−7.3</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. The emission line profiles suggest that both stars are actively accreting, and the dominant accretor is not always the same component, varying in a few orbits.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We constrain the rest-UV size–luminosity relation for star-forming galaxies at <jats:italic>z</jats:italic> ∼ 4 and <jats:italic>z</jats:italic> ∼ 6, 7, and 8 identified behind clusters from the Hubble Frontier Fields (HFF) program. The size–luminosity relation is key to deriving accurate luminosity functions (LF) for faint galaxies. Making use of the latest lensing models and full data set for these clusters, lensing-corrected sizes and luminosities are derived for 68 <jats:italic>z</jats:italic> ∼ 4, 184 <jats:italic>z</jats:italic> ∼ 6, 93 <jats:italic>z</jats:italic> ∼ 7, and 53 <jats:italic>z</jats:italic> ∼ 8 galaxies. We show that size measurements can be reliably measured up to linear magnifications of ∼30×, where the lensing models are well calibrated. The sizes we measure span a &gt;1 dex range, from &lt;50 pc to ≳500 pc. Uncertainties are based on both the formal fit errors and systematic differences between the public lensing models. These uncertainties range from ∼10 pc for the smallest sources to 100 pc for the largest. Using a forward-modeling procedure to model the impact of incompleteness and magnification uncertainties, we characterize the size–luminosity relation at both <jats:italic>z</jats:italic> ∼ 4 and <jats:italic>z</jats:italic> ∼ 6–8. We find that the source sizes of star-forming galaxies at <jats:italic>z</jats:italic> ∼ 4 and <jats:italic>z</jats:italic> ∼ 6–8 scale with luminosity <jats:italic>L</jats:italic> as <jats:italic>L</jats:italic> <jats:sup>0.54±0.08</jats:sup> and <jats:italic>L</jats:italic> <jats:sup>0.40±0.04</jats:sup>, respectively, such that lower-luminosity (≳−18 mag) galaxies are smaller than expected from extrapolating the size–luminosity relation at high luminosities (≲−18 mag). The new evidence for a steeper size–luminosity relation (3<jats:italic>σ</jats:italic>) adds to earlier evidence for small sizes based on the prevalence of highly magnified galaxies in high-shear regions, theoretical arguments against upturns in the LFs, and other independent determinations of the size–luminosity relation from the HFF clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The surfaces of neutron stars are sources of strongly polarized soft X-rays due to the presence of strong magnetic fields. Radiative transfer mediated by electron scattering and free–free absorption is central to defining local surface anisotropy and polarization signatures. Scattering transport is strongly influenced by the complicated interplay between linear and circular polarizations. This complexity has been captured in a sophisticated magnetic Thomson scattering simulation we recently developed to model the outer layers of fully ionized atmospheres in such compact objects, heretofore focusing on case studies of localized surface regions. Yet, the interpretation of observed intensity pulse profiles and their efficacy in constraining key neutron star geometry parameters is critically dependent upon adding up emission from extended surface regions. In this paper, intensity, anisotropy, and polarization characteristics from such extended atmospheres, spanning considerable ranges of magnetic colatitudes, are determined using our transport simulation. These constitute a convolution of varied properties of Stokes parameter information at disparate surface locales with different magnetic field strengths and directions relative to the local zenith. Our analysis includes full general relativistic propagation of light from the surface to an observer at infinity. The array of pulse profiles for intensity and polarization presented highlights how powerful probes of stellar geometry are possible. Significant phase-resolved polarization degrees in the range of 10%–60% are realized when summing over a variety of surface field directions. These results provide an important background for observations to be acquired by NASA’s new Imaging X-ray Polarimetry Explorer X-ray polarimetry mission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Arecibo observations of the bright pulsars B0301+19, B0525+21, B0540+23, B0611+22, and B0823+26 at 1.7 GHz with 100 MHz bandwidth. No giant pulses were found, except for B0823+26, where we recorded a giant interpulse with 230 times the average peak intensity. The postcursor in B0823+26 shows a symmetric double-peaked structure, indicating that it is frequency dependent. In all pulsars, for a given single-pulse peak intensity there is a range of equivalent widths up to a maximum, which becomes smaller the stronger the pulses are, thereby apparently limiting the energy output. Forming average profiles from pulses with certain equivalent widths leads to profiles with changing component characteristics and could allow exploring the magnetosphere at different heights, assuming a dipolar field geometry. We found that the normalized lag-1 autocorrelation coefficient for single-pulse energies can be over 0.5, indicating high correlations. From the first peak of the energy autocorrelation function a so-far-unobserved 15-period modulation is found for B0540+23, as well as a possible 10-period modulation for B0611+22. We also show that a fit of the Weibull distribution to the cumulative probability for the energies yields a better fit than the usual lognormal distribution. The cumulative probability distributions permit an estimate of the nulling fraction, which ranges from 0.6% for B0611+22 to 24% for B0525+21.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using archival infrared data of GLIMPSE, Hi-GAL, and molecular line data of SEDIGISM, MSGPCOS, and MALT90, we investigate the physical and chemical properties of the molecular gas associated with the mid-infrared bubble S156. By the method of spectral energy distribution, we made H<jats:sub>2</jats:sub> column density and dust temperature maps of this region. We find two clouds with masses of 5.4 ± 1.1 × 10<jats:sup>4</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and 2.2 ± 0.5 × 10<jats:sup>4</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, respectively. In both of the two clouds, the <jats:sup>13</jats:sup>CO (2–1/1–0) and <jats:sup>13</jats:sup>CO (2–1)/N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> (1–0) intensity ratios are enhanced on the boundary. Cloud A has a clear dust temperature gradient decreasing from the boundary to the outside region. Our analysis indicates cloud A is mainly influenced by the feedback from S156, while cloud B is affected both by S156 and the G305 complex. We also find the <jats:sup>13</jats:sup>CO and C<jats:sub>2</jats:sub>H emissions tend to be brighter in photon dominated regions (PDRs), while N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> is brighter in the regions of cold gas that is far away. Furthermore, we make the abundance maps of C<jats:sub>2</jats:sub>H and N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> of cloud A. We find the abundance of C<jats:sub>2</jats:sub>H is enhanced in the region facing ionizing stars and it decreases steadily moving away from them. On the other hand, the abundance of N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> increases from the ionized boundary to the cold gas outward. These phenomena indicate C<jats:sub>2</jats:sub>H prefers to be produced in hot gas such as PDRs, while N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> could be destroyed by it. Our study also suggests the abundance ratio of C<jats:sub>2</jats:sub>H to N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> could trace PDRs in the late stages of massive star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Detecting substructure within strongly lensed images is a promising route to shed light on the nature of dark matter. However, it is a challenging task, which traditionally requires detailed lens modeling and source reconstruction, taking weeks to analyze each system. We use machine learning to circumvent the need for lens and source modeling and develop a neural network to both locate subhalos in an image as well as determine their mass using the technique of image segmentation. The network is trained on images with a single subhalo located near the Einstein ring across a wide range of apparent source magnitudes. The network is then able to resolve subhalos with masses <jats:italic>m</jats:italic> ≳ 10<jats:sup>8.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Training in this way allows the network to learn the gravitational lensing of light, and, remarkably, it is then able to detect entire populations of substructure, even for locations further away from the Einstein ring than those used in training. Over a wide range of the apparent source magnitude, the false-positive rate is around three false subhalos per 100 images, coming mostly from the lightest detectable subhalo for that signal-to-noise ratio. With good accuracy and a low false-positive rate, counting the number of pixels assigned to each subhalo class over multiple images allows for a measurement of the subhalo mass function (SMF). When measured over three mass bins from 10<jats:sup>9</jats:sup>–10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> the SMF slope is recovered with an error of 36% for 50 images, and this improves to 10% for 1000 images with Hubble Space Telescope-like noise.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We performed one-dimensional force-free magnetodynamic numerical simulations of the propagation of Alfvén waves along magnetic field lines around a spinning black-hole-like object, the Banados–Teitelboim–Zanelli black string, to investigate the dynamic process of wave propagation and energy transport with Alfvén waves. We considered an axisymmetric and stationary magnetosphere and perturbed the background magnetosphere to obtain the linear wave equation for the Alfvén wave mode. The numerical results show that the energy of Alfvén waves monotonically increases as the waves propagate outwardly along the rotating curved magnetic field line around the ergosphere, where energy seems not to be conserved, in the case of energy extraction from the black string by the Blandford–Znajek mechanism. The apparent breakdown of energy conservation suggests the existence of a wave induced by the Alfvén wave. Considering the additional fast magnetosonic wave induced by the Alfvén wave, the energy conservation is confirmed. Similar relativistic phenomena, such as the amplification of Alfvén waves and induction of fast magnetosonic waves, are expected around a spinning black hole.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It has been widely recognized that gamma-ray burst (GRB) afterglows arise from interactions between the GRB outflow and circumburst medium, while their evolution follows the behaviors of relativistic shock waves. Assuming the distribution of circumburst medium follows a general power-law form, that is, <jats:italic>n</jats:italic> = <jats:italic>A</jats:italic> <jats:sub>*</jats:sub> <jats:italic>R</jats:italic> <jats:sup>−<jats:italic>k</jats:italic> </jats:sup>, where <jats:italic>R</jats:italic> denotes the distance from the burst, it is obvious that the value of the density-distribution index <jats:italic>k</jats:italic> can affect the behaviors of the afterglow. In this paper, we analyze the temporal and spectral behaviors of GRB radio afterglows with arbitrary <jats:italic>k</jats:italic> values. In the radio band, a standard GRB afterglow produced by a forward shock exhibits a late-time flux peak, and the relative peak fluxes, as well as peak times at different frequencies, show dependencies on <jats:italic>k</jats:italic>. Thus, with multiband radio-peak observations, one can determine the density profile of the circumburst medium by comparing the relations between peak flux/time and frequency at each observing band. Also, the effects of transrelativistic shock waves, as well as jets in afterglows, are discussed. By analyzing 31 long and 1 short GRB with multiband data of radio afterglows, we find that nearly half of them can be explained with a uniform interstellar medium (<jats:italic>k</jats:italic> = 0), ∼1/5 can be constrained to exhibiting a stellar-wind environment (<jats:italic>k</jats:italic> = 2), while less than ∼1/3 of the samples show 0 &lt; <jats:italic>k</jats:italic> &lt; 2.</jats:p>