Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We identify shell structures in the Milky Way for the first time. We find two shells in the Virgo Overdensity region and two shells in the Hercules Aquila Cloud region using Sloan Digital Sky Survey, Gaia, and LAMOST data. These shell stars are a subset of the substructure previously identified as the Virgo Radial Merger (VRM). Timing arguments for these shells indicate that their progenitor dwarf galaxy passed through the Galactic center 2.7 ± 0.2 Gyr ago. Based on the time of collision, it is also possible that the VRM is related to the phenomenon that created phase-space spirals in the vertical motion of the disk and/or the Splash and could have caused a burst of star formation in the inner disk. We analyze phase mixing in a collection of radial merger <jats:italic>N</jats:italic>-body simulations and find that shell structure similar to that observed in Milky Way data disappears by 5 Gyr after collision with the Galactic center. The method used to calculate the merger time of the VRM was able to reliably recover the correct merger times for these simulations. Previous work supports the idea that the VRM and the Gaia Sausage/Gaia–Enceladus Merger are the same. However, the Gaia Sausage is widely believed to be 8–11 Gyr old. The disparate ages could be reconciled if the larger age is associated with an infall time when the progenitor crossed the virial radius; we do not constrain the time at which the progenitor became bound to the Milky Way. Alternatively, the Gaia Sausage could be younger than previously thought.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the postmerger mass ejection of low-mass binary neutron stars (NSs) with the system mass of 2.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and subsequent nucleosynthesis by performing general-relativistic, neutrino-radiation viscous-hydrodynamics simulations in axial symmetry. We find that the merger remnants are long-lived massive NSs surviving more than several seconds, irrespective of the nuclear equations of state (EOSs) adopted. The ejecta masses of our fiducial models are ∼0.06–0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> (depending on the EOS), being ∼30% of the initial disk masses (∼0.15–0.3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>). Postprocessing nucleosynthesis calculations indicate that the ejecta is composed mainly of light <jats:italic>r</jats:italic>-process nuclei with small amounts of lanthanides (mass fraction ∼0.002–0.004) and heavier species due to the modest average electron fraction (∼0.32–0.34) for a reasonable value of the viscous coefficient. Such abundance distributions are compatible with those in weak <jats:italic>r</jats:italic>-process stars such as HD 122563 but not with the solar <jats:italic>r</jats:italic>-process-like abundance patterns found in all measured <jats:italic>r</jats:italic>-process-enhanced metal-poor stars. Therefore, low-mass binary NS mergers should be rare. If such low-mass NS mergers occur, their electromagnetic counterparts, kilonovae, will be characterized by an early bright blue emission because of the large ejecta mass as well as the small lanthanide fraction. We also show, however, that if the effective turbulent viscosity is very high, the electron fraction of the ejecta could be low enough that the solar <jats:italic>r</jats:italic>-process-like abundance pattern is reproduced and the lanthanide fraction becomes so high that the kilonova would be characterized by early bright blue and late bright red emissions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of 59 new ghostly absorbers from the Sloan Digital Sky Survey Data Release 14. These absorbers, with <jats:italic>z</jats:italic> <jats:sub>abs</jats:sub> ∼ <jats:italic>z</jats:italic> <jats:sub>QSO</jats:sub>, reveal no Ly<jats:italic>α</jats:italic> absorption, and they are mainly identified through the detection of strong metal absorption lines in the spectra. The number of such previously known systems is 30. The new systems are found with the aid of machine-learning algorithms. The spectra of 41 (out of total of 89) absorbers also cover the Ly<jats:italic>β</jats:italic> spectral region. By fitting the damping wings of the Ly<jats:italic>β</jats:italic> absorption in the stacked spectrum of 21 (out of 41) absorbers with relatively stronger Ly<jats:italic>β</jats:italic> absorption, we measured an H <jats:sc>i</jats:sc> column density of log <jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) = 21.50. This column density is 0.5 dex higher than that of the previous work. We also found that the metal absorption lines in the stacked spectrum of the 21 ghostly absorbers with stronger Ly<jats:italic>β</jats:italic> absorption have similar properties as those in the stacked spectrum of the remaining systems. This circumstantial evidence strongly suggests that the majority of our ghostly absorbers are indeed DLAs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A third object in the vicinity of a binary system causes variations in the eccentricity and the inclination of the binary through the Kozai–Lidov (KL) effect. We examine if such variations leave a detectable imprint on the gravitational waves of a binary consisting of intermediate-mass black holes and stellar-mass objects. As a proof of concept, we present an example where LISA may detect the KL-modulated gravitational wave signals of such sources from at least a distance of 1 Mpc if the perturbation is caused by a supermassive black hole tertiary. Although the quick pericenter precession induced by general relativity significantly reduces the appropriate parameter space for this effect by quenching the KL oscillations, we still find reasonable parameters where the KL effect may be detected with high signal-to-noise ratios.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The thermal Sunyaev–Zel’dovich (tSZ) and the kinematic Sunyaev–Zel’dovich (kSZ) effects trace the distribution of electron pressure and momentum in the hot universe. These observables depend on rich multiscale physics, thus, simulated maps should ideally be based on calculations that capture baryonic feedback effects such as cooling, star formation, and other complex processes. In this paper, we train deep convolutional neural networks with a U-Net architecture to map from the three-dimensional distribution of dark matter to electron density, momentum, and pressure at ∼100 kpc resolution. These networks are trained on a combination of the TNG300 volume and a set of cluster zoom-in simulations from the IllustrisTNG project. The neural nets are able to reproduce the power spectrum, one-point probability distribution function, bispectrum, and cross-correlation coefficients of the simulations more accurately than the state-of-the-art semianalytical models. Our approach offers a route to capture the richness of a full cosmological hydrodynamical simulation of galaxy formation with the speed of an analytical calculation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of the central radio activity of galaxy clusters at high redshift. Using a large sample of galaxy clusters at 0.7 &lt; <jats:italic>z</jats:italic> &lt; 1.5 from the Massive and Distant Clusters of Wide-field Infrared Survey Explorer Survey and the Faint Images of the Radio Sky at Twenty-Centimeters 1.4 GHz catalog, we measure the fraction of clusters containing a radio source within the central 500 kpc, which we term the cluster radio-active fraction, and the fraction of cluster galaxies within the central 500 kpc exhibiting radio emission. We find tentative (2.25<jats:italic>σ</jats:italic>) evidence that the cluster radio-active fraction increases with cluster richness, while the fraction of cluster galaxies that are radioluminous (<jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{1.4\mathrm{GHz}}\geqslant {10}^{25}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb08dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> W Hz<jats:sup>−1</jats:sup>) does not correlate with richness at a statistically significant level. Compared to that calculated at 0 &lt; <jats:italic>z</jats:italic> &lt; 0.6, the cluster radio-active fraction at 0 &lt; <jats:italic>z</jats:italic> &lt; 1.5 increases by a factor of 10. This fraction is also dependent on the radio luminosity. Clusters at higher redshift are much more likely to host a radio source of luminosity <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{1.4\mathrm{GHz}}\gtrsim {10}^{26}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb08dieqn2.gif" xlink:type="simple" /> </jats:inline-formula> W Hz<jats:sup>−1</jats:sup> than are lower-redshift clusters. We compare the fraction of radioluminous cluster galaxies to the fraction measured in a field environment. For 0.7 &lt; <jats:italic>z</jats:italic> &lt; 1.5, we find that both the cluster and field radioluminous galaxy fraction increases with stellar mass, regardless of environment, though at fixed stellar mass, cluster galaxies are roughly 2 times more likely to be radioluminous than field galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The initial separation of massive star binaries sets the timescale over which their compact remnants merge through the emission of gravitational waves. We show that the delay time distribution (DTD) of binary neutron stars or black holes can be inferred from the stochastic gravitational wave background (SGWB). If the DTD of a population is long, most of the mergers take place at low redshifts and the background would be rather quiet compared to a scenario in which the DTD is short leading to few individual detections at low redshift but a rather loud background. We show that different DTDs predict a factor of 5 difference in the magnitude of the gravitational wave background energy density (<jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{\mathrm{GW}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and have the dominant effect on <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{\mathrm{GW}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn2.gif" xlink:type="simple" /> </jats:inline-formula> over other factors such as the mass function of the primary BH mass, <jats:inline-formula> <jats:tex-math> <?CDATA $p({m}_{1})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, the maximum considered BH mass (<jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\max }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn4.gif" xlink:type="simple" /> </jats:inline-formula>), and the effective spin of the black hole (<jats:inline-formula> <jats:tex-math> <?CDATA ${\chi }_{\mathrm{eff}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn5.gif" xlink:type="simple" /> </jats:inline-formula>). A nondetection of such a background can rule out the short DTD scenario. We show that SGWB searches can rule out the short DTD scenario for the BBHs within about four years of observing time at advanced LIGO design sensitivity for a local merger rate of 30 <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn6.gif" xlink:type="simple" /> </jats:inline-formula> assuming <jats:inline-formula> <jats:tex-math> <?CDATA $p({m}_{1})\propto {m}_{1}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn7.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\max }=50{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb1afieqn8.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>M<jats:sc>etacalibration</jats:sc> is a new technique for measuring weak gravitational lensing shear that is unbiased for isolated galaxy images. In this work we test <jats:sc>metacalibration</jats:sc> with overlapping, or “blended” galaxy images. Using standard <jats:sc>metacalibration</jats:sc>, we find a few percent shear measurement bias for galaxy densities relevant for current surveys, and that this bias increases with increasing galaxy number density. We show that this bias is not due to blending itself, but rather to shear-dependent object detection. If object detection is shear-independent, no deblending of images is needed, in principle. We demonstrate that detection biases are accurately removed when including object detection in the <jats:sc>metacalibration</jats:sc> process, a technique we call <jats:sc>metadetection</jats:sc>. This process involves applying an artificial shear to images of small regions of sky and performing detection on the sheared images, as well as measurements that are used to calculate a shear response. We demonstrate that the method can accurately recover weak shear signals even in highly blended scenes. In the <jats:sc>metacalibration</jats:sc> process, the space between objects is sheared coherently, which does not perfectly match the real universe in which some, but not all, galaxy images are sheared coherently. We find that even for the worst case scenario, in which the space between objects is completely unsheared, the resulting shear bias is at most a few tenths of a percent for future surveys. We discuss additional technical challenges that must be met in order to implement <jats:sc>metadetection</jats:sc> for real surveys.</jats:p>