Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The equations of state of the neutron star at the hadron-quark crossover region are interpolated with the Gaussian process regression (GPR) method, which can reduce the randomness of present interpolation schemes. The relativistic mean-field (RMF) model and Nambu–Jona-Lasinio (NJL) model are employed to describe the hadronic phase and quark phase, respectively. In the RMF model, the coupling term between <jats:italic>ω</jats:italic> and <jats:italic>ρ</jats:italic> mesons is considered to control the density-dependent behaviors of symmetry energy, i.e., the slope of symmetry energy <jats:italic>L</jats:italic>. Furthermore, the vector interaction between quarks is included in the NJL model to obtain the additional repulsive contributions. Their coupling strengths and the crossover windows are discussed in the present framework under the constraints on the neutron star from gravitational-wave detections, massive neutron star measurements, mass–radius simultaneous observation of the NICER Collaboration, and the neutron skin thickness of <jats:sup>208</jats:sup>Pb from PREX-II. It is found that the slope of symmetry energy, <jats:italic>L</jats:italic>, should be around 50−90 MeV and the crossover window is (0.3, 0.6) fm<jats:sup>−3</jats:sup> with these observables. Furthermore, the uncertainties of neutron star masses and radii in the hadron-quark crossover regions are also predicted by the GPR method.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the detection of an ionized gas outflow from an X-ray active galactic nucleus hosted in a massive quiescent galaxy in a protocluster at <jats:italic>z</jats:italic> = 3.09 (J221737.29+001823.4). It is a type-2 QSO with broad (<jats:italic>W</jats:italic> <jats:sub>80</jats:sub> &gt; 1000 km s<jats:sup>−1</jats:sup>) and strong (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({L}_{[\mathrm{OIII}]}$?> </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>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">[</mml:mo> <mml:mi>OIII</mml:mi> <mml:mo stretchy="false">]</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7f2dieqn1.gif" xlink:type="simple" /> </jats:inline-formula>/erg s<jats:sup>−1</jats:sup>) ≈ 43.4) [O <jats:sc>iii</jats:sc>]<jats:italic>λ</jats:italic> <jats:italic>λ</jats:italic> 4959,5007 emission lines detected by slit spectroscopy in three-position angles using Multi-Object Infra-Red Camera and Spectrograph (MOIRCS) on the Subaru telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) on the Keck-I telescope. In the all slit directions, [O <jats:sc>iii</jats:sc>] emission is extended to ∼15 physical kpc and indicates a powerful outflow spreading over the host galaxy. The inferred ionized gas mass outflow rate is 22 ± 3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. Although it is a radio source, according to the line diagnostics using H<jats:italic>β</jats:italic>, [O <jats:sc>ii</jats:sc>], and [O <jats:sc>iii</jats:sc>], photoionization by the central QSO is likely the dominant ionization mechanism rather than shocks caused by radio jets. On the other hand, the spectral energy distribution of the host galaxy is well characterized as a quiescent galaxy that has shut down star formation several hundred Myr ago. Our results suggest a scenario that QSOs are powered after the shutdown of the star formation and help complete the quenching of massive quiescent galaxies at high redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, six convolutional neural networks (CNNs) have been trained based on 15,638 superflare candidates on solar-type stars, which are collected from the three years of Transiting Exoplanet Survey Satellite (TESS) observations. These networks are used to replace the manually visual inspection, which was a direct way of searching for superflares, and exclude false-positive events in recent years. Unlike other methods, which only used stellar light curves to search for superflare signals, we try to identify superflares through TESS pixel-level data with lower risk of mixing false-positive events and give more reliable identification results for statistical analysis. The evaluated accuracy of each network is around 95.57%. After applying ensemble learning to these networks, the stacking method promotes accuracy to 97.62% with a 100% classification rate, and the voting method promotes accuracy to 99.42% with a relatively lower classification rate at 92.19%. We find that superflare candidates with short duration and low peak amplitude have lower identification precision, as their superflare features are hard to be identified. The database includes 71,732 solar-type stars and 15,638 superflare candidates from TESS with corresponding feature images and arrays, and the trained CNNs in this work are public available.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the simple but robust model of a shell of dark matter (DM) around a Schwarzschild black hole (BH), represented by the mass ratio of the shell and BH Δ<jats:italic>M</jats:italic>/<jats:italic>M</jats:italic>, the shell extension Δ<jats:italic>r</jats:italic> <jats:sub>s</jats:sub> and its inner radius <jats:italic>r</jats:italic> <jats:sub>s</jats:sub>, we study the influence of DM on the spacetime structure and geodesic motion, and provide a classification of the BH+DM shell spacetimes according to the properties of the stable circular geodesics governing Keplerian disks. We focus our attention on the epicyclic motion around circular geodesics that can be related to observational phenomena in X-ray radiation from Keplerian accretion disks, assumed to be influenced by the DM shell only gravitationally. We give the frequencies of the orbital and epicyclic motions and discuss their properties in terms of the parameters governing the DM shell. Using the frequencies in relevant variants of the standard geodesic model of high-frequency quasiperiodic oscillations (HF QPOs), we test the role of DM by fitting the HF QPO data from some microquasars and active galactic nuclei with supermassive BHs where no variant of the geodesic model applied in the standard vacuum BH background is able to explain the data. We thus provide a robust review of the applicability of the geodesic model of HF QPOs, and also provide limits on the amount of DM around a BH. We demonstrate that the geodesic model could be well applied to most observations of active galactic nuclei, with strong restrictions on the amount of invisible matter around BHs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the results of an analysis of the H<jats:italic>β</jats:italic> emission line region of a sample of 30 low-redshift (<jats:italic>z</jats:italic> &lt; 1) iron low-ionization broad absorption line quasars (FeLoBALQs). Eleven of these objects are newly classified as FeLoBALQs. A matched sample of 132 unabsorbed quasars was analyzed in parallel. The emission lines showed the well-known anticorrelation between the [O <jats:sc>iii</jats:sc>] and Fe <jats:sc>ii</jats:sc> emission. Using a summary statistic called <jats:italic>E</jats:italic>1 to quantify this anticorrelation, we found that while the distribution of <jats:italic>E</jats:italic>1 for the unabsorbed quasars has a single peak, the FeLoBALQs have a bimodal shape in this parameter. Previous studies have shown that the line emission properties of BAL and non-BALQs are consistent; therefore, the difference in the H<jats:italic>β</jats:italic> region emission between FeLoBALQs and unabsorbed quasars is a new result. The two populations of FeLoBALQs are characterized by low and high bolometric luminosities and Eddington ratios. Some previous studies have suggested that BALQs are high accretion rate objects and therefore the discovery of the low accretion rate branch of FeLoBAL quasars was unexpected. We also found that the H<jats:italic>β</jats:italic> FWHM is systematically broader among the FeLoBALQs, implying a higher inclination viewing angle or a dearth of low velocity line emitting gas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>AMEGO-X, the All-sky Medium Energy Gamma-ray Observatory eXplorer, is a proposed instrument designed to bridge the so-called “MeV gap” by surveying the sky with unprecedented sensitivity from ∼100 keV to about 1 GeV. This energy band is of key importance for multimessenger and multiwavelength studies but it is nevertheless currently underexplored. AMEGO-X addresses this situation by proposing a design capable of detecting and imaging gamma rays via both Compton interactions and pair production processes. However, some of the objects that AMEGO-X will study, such as gamma-ray bursts and magnetars, extend to energies below ∼100 keV where the dominant interaction becomes photoelectric absorption. These events deposit their energy in a single pixel of the detector. In this work we show how the ∼3500 cm<jats:sup>2</jats:sup> effective area of the AMEGO-X tracker to events between ∼25 and ∼100 keV will be utilized to significantly improve its sensitivity and expand the energy range for transient phenomena. Although imaging is not possible for single-site events, we show how we will localize a transient source in the sky using their aggregate signal to within a few degrees. This technique will more than double the number of cosmological gamma-ray bursts seen by AMEGO-X, allow us to detect and resolve the pulsating tails of extragalactic magnetar giant flares, and increase the number of detected less-energetic magnetar bursts—some possibly associated with fast radio bursts. Overall, single-site events will increase the sensitive energy range, expand the science program, and promptly alert the community of fainter transient events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The UV/optical variability of active galactic nuclei (AGN) has long been thought to be driven by the X-ray illumination of the accretion disk. However, recent multiwavelength campaigns of nearby Seyfert galaxies seem to challenge this paradigm, with an apparent discrepancy between observations and the underlying theory. In order to further probe the connection between the UV/optical and X-ray variability in AGN, we developed a physical model to reproduce the UV/optical power spectral densities (PSDs) of AGN assuming the thermal reprocessing of the X-rays in the disk. This model offers a novel way to probe the innermost regions of AGN. We use our model to study the variability of NGC 5548, and we infer that the X-ray and UV/optical PSDs as well as the interband UV/optical time lags are all well reproduced. We also derive constraints on the source physical parameters, such as the X-ray corona height and the accretion rate. Our results suggest that X-ray disk reprocessing accounts for the full variability properties of this AGN, within the considered timescales. Using earlier data of NGC 5548, we also show that our model can reproduce its PSD in different epochs, establishing the feasibility of using PSD modeling to investigate the time evolution of a source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recently, a new class of white dwarfs (“slowly cooling WDs”) has been identified in the globular cluster M13. The cooling time of these stars is increased by stable thermonuclear hydrogen burning in their residual envelope. These WDs are thought to be originated by horizontal branch (HB) stars populating the HB blue tail that skipped the asymptotic giant branch phase. To further explore this phenomenon, we took advantage of deep photometric data acquired with the Hubble Space Telescope in the near-ultraviolet and investigate the bright portion of the WD cooling sequence in NGC 6752, another Galactic globular cluster with a metallicity, age, and HB morphology similar to M13. The normalized WD luminosity function derived in NGC 6752 turns out to be impressively similar to that observed in M13, in agreement with the fact that the stellar mass distribution along the HB of these two systems is almost identical. As in the case of M13, the comparison with theoretical predictions is consistent with ∼70% of the investigated WDs evolving at slower rates than standard, purely cooling WDs. Thanks to its relatively short distance from Earth, NGC 6752 photometry reaches a luminosity 1 order of a magnitude fainter than the case of M13, allowing us to sample a regime where the cooling time delay, with respect to standard WD models, reaches ∼300 Myr. The results presented in this paper provide new evidence for the existence of slowly cooling WDs and further support to the scenario proposing a direct causal connection between this phenomenon and the HB morphology of the host stellar cluster.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We measure, for the first time, the median equivalent width (EW) of H<jats:italic>α</jats:italic>+[N <jats:sc>ii</jats:sc>] in star-forming galaxies at <jats:italic>z</jats:italic> ∼ 8. Our estimate leverages the unique photometric depth of the Spitzer/IRAC 5.8 <jats:italic>μ</jats:italic>m band mosaics (probing ≈5500–7100 Å at <jats:italic>z</jats:italic> ∼ 8) of the GOODS Reionization Era Wide Area Treasury from Spitzer (GREATS) program. We median-stacked the stamps of 102 Lyman-break galaxies in the 3.6, 4.5, 5.8, and 8.0 <jats:italic>μ</jats:italic>m bands, after carefully removing potential contamination from neighboring sources. We infer an extreme rest-frame EW<jats:sub>0</jats:sub>(H<jats:italic>α</jats:italic>+[N <jats:sc>ii</jats:sc>]) = <jats:inline-formula> <jats:tex-math> <?CDATA ${2328}_{-1127}^{+1326}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2328</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1127</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1326</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7e44ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Å from the measured red [3.6] − [5.8] = 0.82 ± 0.27 mag, consistent with young (≲10<jats:sup>7</jats:sup> yr) average stellar population ages at <jats:italic>z</jats:italic> ∼ 8. This implies an ionizing photon production efficiency of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{l}}{\rm{o}}{\rm{g}}({\xi }_{{\rm{i}}{\rm{o}}{\rm{n}},0}/{\rm{e}}{\rm{r}}{\rm{g}}\,{{\rm{H}}{\rm{z}}}^{-1})={25.97}_{-0.28}^{+0.18}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">l</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">g</mml:mi> </mml:mrow> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>,</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">g</mml:mi> </mml:mrow> </mml:mrow> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">z</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>25.97</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.28</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.18</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7e44ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Such a high value for photoproduction, similar to the highest values found at <jats:italic>z</jats:italic> ≲ 4, indicates that only modest escape fractions <jats:italic>f</jats:italic> <jats:sub>esc</jats:sub> ≲ 0.3 (at 2<jats:italic>σ</jats:italic>) are sufficient for galaxies brighter than <jats:italic>M</jats:italic> <jats:sub>UV</jats:sub> &lt; −18 mag to reionize the neutral hydrogen at <jats:italic>z</jats:italic> ∼ 8. This requirement is relaxed even more to <jats:italic>f</jats:italic> <jats:sub>esc</jats:sub> ≤ 0.1 when considering galaxies brighter than <jats:italic>M</jats:italic> <jats:sub>UV</jats:sub> ≈ −13 mag, consistent with recent luminosity functions and as typically assumed in studies addressing reionization. These exceptional results clearly indicate that galaxies can be the dominant source of reionizing photons, and provide us with an exciting glimpse into what we might soon learn about the early universe, and particularly about the reionization epoch, from forthcoming JWST/MIRI and NIRCam programs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analysis of the mid-infrared spectra, obtained from the Spitzer Space Telescope, of the dark globule DC 314.8–5.1, which is at the onset of low-mass star formation. The target has a serendipitous association with a B-type field star that illuminates a reflection nebula in the cloud. We focus on the polycyclic aromatic hydrocarbon (PAH) emission features prevalent throughout the mid-infrared range. The analysis of the spectra with the PAHFIT software as well as with the pypahdb package shows that (i) the intensities of PAH features decrease over distance from the ionizing star toward the cloud center, with some however showing a saturation at larger distances; (ii) the relative intensities of the 6.2 and 8.6 features with respect to the 11.2 <jats:italic>μ</jats:italic>m feature remain high throughout the globule, suggesting a higher cation-to-neutral PAH ratio of the order of unity; the breakdown from pypahdb confirms a high ionized fraction within the cloud; (iii) the pypahdb results display a decrease in large-PAH fraction with increased distance from HD 130079, as well as a statistically significant correlation between the large-size fraction and the ionized fraction across the globule; (iv) the 7.7 PAH feature displays a peak nearer to 7.8 <jats:italic>μ</jats:italic>m, suggesting a chemically processed PAH population with a small fraction of UV-processed PAHs; and (v) the H<jats:sub>2</jats:sub> S(0) line is detected at larger distances from the ionizing star. All in all, our results suggest divergent physical conditions within the quiescent cloud DC 314.8–5.1 as compared to molecular clouds with ongoing star formation.</jats:p>