Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Tidal disruption events (TDEs) provide a unique opportunity to probe the stellar populations around supermassive black holes (SMBHs). By combining light-curve modeling with spectral line information and knowledge about the stellar populations in the host galaxies, we are able to constrain the properties of the disrupted star for three TDEs. The TDEs in our sample have UV spectra, and measurements of the UV N <jats:sc>iii</jats:sc> to C <jats:sc>iii</jats:sc> line ratios enabled estimates of the nitrogen-to-carbon abundance ratios for these events. We show that the measured nitrogen line widths are consistent with originating from the disrupted stellar material dispersed by the central SMBH. We find that these nitrogen-to-carbon abundance ratios necessitate the disruption of moderately massive stars (≳1–2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>). We determine that these moderately massive disruptions are overrepresented by a factor of ≳10<jats:sup>2</jats:sup> when compared to the overall stellar population of the post-starburst galaxy hosts. This implies that SMBHs are preferentially disrupting higher mass stars, possibly due to ongoing top-heavy star formation in nuclear star clusters or to dynamical mechanisms that preferentially transport higher mass stars to their tidal radii.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We search for H<jats:italic>α</jats:italic> emitters at <jats:italic>z</jats:italic> ∼ 7.8 in four gravitationally lensed fields observed in the Hubble Frontier Fields program. We use the Lyman break method to select galaxies at the target redshift and perform photometry in the Spitzer/IRAC 5.8 <jats:italic>μ</jats:italic>m band to detect H<jats:italic>α</jats:italic> emission from the candidate galaxies. We find no significant detections of counterparts in the IRAC 5.8 <jats:italic>μ</jats:italic>m band, and this gives a constraint on the H<jats:italic>α</jats:italic> luminosity function (LF) at <jats:italic>z</jats:italic> ∼ 7.8. We compare the constraint with previous studies based on rest-frame UV and far-infrared observations using the correlation between the H<jats:italic>α</jats:italic> luminosity and the star formation rate. Additionally, we convert the constraint on the H<jats:italic>α</jats:italic> LF into an upper limit for the star formation rate density (SFRD) at this epoch assuming the shape of the LF. We examine two types of parameterization of the LF and obtain an upper limit for the SFRD of <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}({\rho }_{\mathrm{SFR}}\ [{M}_{\odot }\,{\mathrm{yr}}^{-1}\ {\mathrm{Mpc}}^{-3}])\lesssim -1.1$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>SFR</mml:mi> </mml:mrow> </mml:msub> <mml:mspace width="0.33em" /> <mml:mo stretchy="false">[</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em" /> <mml:msup> <mml:mrow> <mml:mi>Mpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">]</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≲</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1.1</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac356aieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at <jats:italic>z</jats:italic> ∼ 7.8. With this constraint on the SFRD, we present an independent probe into the total star formation activity including dust-obscured and unobscured star formation at the Epoch of Reionization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gas morphology and kinematics in the Milky Way contain key information for understanding the formation and evolution of our Galaxy. We present hydrodynamical simulations based on realistic barred Milky Way potentials constrained by recent observations. Our model can reproduce most features in the observed longitude–velocity diagram, including the Central Molecular Zone, the Near and Far 3 kpc arms, the Molecular Ring, and the spiral arm tangents. It can also explain the noncircular motions of masers from the recent BeSSeL2 survey. The central gas kinematics are consistent with a mass of 6.9 × 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> in the Nuclear Stellar Disk. Our model predicts the formation of an elliptical gaseous ring surrounding the bar, which is composed of the 3 kpc arms, the Norma arm, and the bar-spiral interfaces. This ring is similar to those “inner” rings in some Milky Way analogs with a boxy/peanut-shaped bulge (e.g., NGC 4565 and NGC 5746). The kinematics of gas near the solar neighborhood are governed by the Local arm. The bar pattern speed constrained by our gas model is 37.5–40 km s<jats:sup>−1</jats:sup> kpc<jats:sup>−1</jats:sup>, corresponding to a corotation radius of <jats:italic>R</jats:italic> <jats:sub>CR</jats:sub> = 6.0–6.4 kpc. The rotation curve of our model rises gently within the central ∼ 5 kpc, significantly less steep than those predicted by some recent zoom-in cosmological simulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The continuum-fitting and the iron-line methods are currently the two leading techniques for measuring the spins of accreting black holes. In the past few years, these two methods have been developed for testing fundamental physics. In the present work, we employ state-of-the-art models to test black holes through the continuum-fitting and the iron-line methods and we analyze three NuSTAR observations of the black hole binary GRS 1716-249 during its outburst in 2016–2017. In these three observations, the source was in a hard-intermediate state and the spectra show both a strong thermal component and prominent relativistic reflection features. Our analysis confirms the Kerr nature of the black hole in GRS 1716-249 and provides quite stringent constraints on possible deviations from the predictions of general relativity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The CO-to-H<jats:sub>2</jats:sub> conversion factor (<jats:italic>α</jats:italic> <jats:sub>CO</jats:sub>) is critical to studying molecular gas and star formation in galaxies. The value of <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> has been found to vary within and between galaxies, but the specific environmental conditions that cause these variations are not fully understood. Previous observations on ~kiloparsec scales revealed low values of <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> in the centers of some barred spiral galaxies, including NGC 3351. We present new Atacama Large Millimeter/submillimeter Array Band 3, 6, and 7 observations of <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, and C<jats:sup>18</jats:sup>O lines on 100 pc scales in the inner ∼2 kpc of NGC 3351. Using multiline radiative transfer modeling and a Bayesian likelihood analysis, we infer the H<jats:sub>2</jats:sub> density, kinetic temperature, CO column density per line width, and CO isotopologue abundances on a pixel-by-pixel basis. Our modeling implies the existence of a dominant gas component with a density of 2–3 × 10<jats:sup>3</jats:sup> cm<jats:sup>−3</jats:sup> in the central ∼1 kpc and a high temperature of 30–60 K near the nucleus and near the contact points that connect to the bar-driven inflows. Assuming a CO/H<jats:sub>2</jats:sub> abundance of 3 × 10<jats:sup>−4</jats:sup>, our analysis yields <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> ∼ 0.5–2.0 <jats:italic>M</jats:italic> <jats:sub>⊙ </jats:sub>(K km s<jats:sup>−1</jats:sup> pc<jats:sup>2</jats:sup>)<jats:sup>−1</jats:sup> with a decreasing trend with galactocentric radius in the central ∼1 kpc. The inflows show a substantially lower <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> ≲ 0.1 <jats:italic>M</jats:italic> <jats:sub>⊙ </jats:sub>(K km s<jats:sup>−1 </jats:sup>pc<jats:sup>2</jats:sup>)<jats:sup>−1</jats:sup>, likely due to lower optical depths caused by turbulence or shear in the inflows. Over the whole region, this gives an intensity-weighted <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> of ∼1.5 <jats:italic>M</jats:italic> <jats:sub>⊙ </jats:sub>(K km s<jats:sup>−1 </jats:sup>pc<jats:sup>2</jats:sup>)<jats:sup>−1</jats:sup>, which is similar to previous dust-modeling-based results at kiloparsec scales. This suggests that low <jats:italic>α</jats:italic> <jats:sub>CO</jats:sub> on kiloparsec scales in the centers of some barred galaxies may be due to the contribution of low-optical-depth CO emission in bar-driven inflows.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The ratio of <jats:italic>α</jats:italic>-elements to iron in galaxies holds valuable information about the star formation history (SFH) since their enrichment occurs on different timescales. The fossil record of stars in galaxies has mostly been excavated for passive galaxies, since the light of star-forming galaxies is dominated by young stars, which have much weaker atmospheric absorption features. Here we use the largest reference cosmological simulation of the EAGLE project to investigate the origin of variations in stellar <jats:italic>α</jats:italic>-enhancement among star-forming galaxies at <jats:italic>z</jats:italic> = 0, and their impact on integrated spectra. The definition of <jats:italic>α</jats:italic>-enhancement in a composite stellar population is ambiguous. We elucidate two definitions—termed “mean” and “galactic” <jats:italic>α</jats:italic>-enhancement—in more detail. While a star-forming galaxy has a high “mean” <jats:italic>α</jats:italic>-enhancement when its stars formed rapidly, a galaxy with a large “galactic” <jats:italic>α</jats:italic>-enhancement generally had a delayed SFH. We find that absorption-line strengths of Mg and Fe correlate with variations in <jats:italic>α</jats:italic>-enhancement. These correlations are strongest for the “galactic” <jats:italic>α</jats:italic>-enhancement. However, we show that these are mostly caused by other effects that are cross-correlated with <jats:italic>α</jats:italic>-enhancement, such as variations in the light-weighted age. This severely complicates the retrieval of <jats:italic>α</jats:italic>-enhancements in star-forming galaxies. The ambiguity is not severe for passive galaxies, and we confirm that spectral variations in these galaxies are caused by measurable variations in <jats:italic>α</jats:italic>-enhancements. We suggest that this more complex coupling between <jats:italic>α</jats:italic>-enhancement and SFHs can guide the interpretation of new observations of star-forming galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many astrophysical phenomena are time-varying, in the sense that their brightness changes over time. In the case of periodic stars, previous approaches assumed that changes in period, amplitude, and phase are well described by either parametric or piecewise-constant functions. With this paper, we introduce a new mathematical model for the description of the so-called <jats:italic>modulated</jats:italic> light curves, as found in periodic variable stars that exhibit <jats:italic>smoothly</jats:italic> time-varying parameters such as amplitude, frequency, and/or phase. Our model accounts for a smoothly time-varying trend and a harmonic sum with smoothly time-varying weights. In this sense, our approach is flexible because it avoids restrictive assumptions (parametric or piecewise-constant) about the functional form of the trend and amplitudes. We apply our methodology to the light curve of a pulsating RR Lyrae star characterized by the Blazhko effect. To estimate the time-varying parameters of our model, we develop a semi-parametric method for unequally spaced time series. The estimation of our time-varying curves translates into the estimation of time-invariant parameters that can be performed by ordinary least squares, with the following two advantages: modeling and forecasting can be implemented in a parametric fashion, and we are able to cope with missing observations. To detect serial correlation in the residuals of our fitted model, we derive the mathematical definition of the spectral density for unequally spaced time series. The proposed method is designed to estimate smoothly time-varying trends and amplitudes, as well as the spectral density function of the errors. We provide simulation results and applications to real data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In a protocluster USS1558-003 at <jats:italic>z</jats:italic> = 2.53, galaxies in the dense cores show systematically elevated star-forming activity compared to those in less dense regions. To understand its origin, we look into the gas properties of the galaxies in the dense cores by conducting deep 1.1 mm observations with the Atacama Large Millimeter/submillimeter Array. We detect interstellar dust continuum emission from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from the CO(3–2) line, we infer that the latter might be overestimated. We find that the gas to stellar mass ratios of the galaxies in the dense cores tend to be higher (at <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ∼ 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> where we see the enhanced star-forming activity), suggesting that such large gas masses can sustain their high star-forming activity. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at a similar cosmic epoch, we find no significant environmental difference at the same stellar mass and star formation rate. Although both gas mass ratios and star-forming activity are enhanced in the majority of member galaxies, they appear to follow the same scaling relation as field galaxies. Our results are consistent with the scenario in which the cold gas is efficiently supplied to protocluster cores and to galaxies therein along surrounding filamentary structures, which leads to the high gas mass fractions and thus the elevated star formation activity, but without changing the star formation law.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a comparative study of X-ray and IR active galactic nuclei (AGNs) at <jats:italic>z</jats:italic> ≈ 2 to highlight the important AGN selection effects on the distributions of host-galaxy properties. Compared with non-AGN star-forming galaxies (SFGs) on the main sequence, X-ray AGNs have similar median star formation (SF) properties, but their incidence (<jats:italic>q</jats:italic> <jats:sub>AGN</jats:sub>) is higher among galaxies with either enhanced or suppressed SF, and among galaxies with a larger stellar-mass surface density, regardless if it is measured within the half-light radius (Σ<jats:sub> <jats:italic>e</jats:italic> </jats:sub>) or central 1 kpc (Σ<jats:sub>1kpc</jats:sub>). Unlike X-ray AGNs, IR AGNs are less massive and have enhanced SF and similar distributions of colors, Σ<jats:sub> <jats:italic>e</jats:italic> </jats:sub> and Σ<jats:sub>1kpc</jats:sub>, relative to non-AGN SFGs. Given that Σ<jats:sub> <jats:italic>e</jats:italic> </jats:sub> and Σ<jats:sub>1kpc</jats:sub> strongly correlate with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>, we introduce the fractional mass within the central 1 kpc (<jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{1{\rm{kpc}}}/{M}_{\ast }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mi mathvariant="normal">kpc</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>∗</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3837ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), which only weakly depends on <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>, to quantify galaxy compactness. Both AGN populations have similar <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{1{\rm{kpc}}}/{M}_{\ast }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mi mathvariant="normal">kpc</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>∗</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3837ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> distributions compared to non-AGN SFGs’. While <jats:italic>q</jats:italic> <jats:sub>AGN</jats:sub> increases with Σ<jats:sub> <jats:italic>e</jats:italic> </jats:sub> and Σ<jats:sub>1kpc</jats:sub>, it remains constant with <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{1{\rm{kpc}}}/{M}_{\ast }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mi mathvariant="normal">kpc</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>∗</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3837ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, indicating that the trend of increasing <jats:italic>q</jats:italic> <jats:sub>AGN</jats:sub> with Σ is driven by <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> more than morphology. While our findings are not in conflict with the scenario of AGN quenching, they do not imply it either, because the incidence of AGNs hosted in transitional galaxies depends crucially on AGN selections. Additionally, despite the relatively large uncertainty of AGN bolometric luminosities, their very weak correlation, if any, with SF activities, regardless of AGN selections, also argues against a direct causal link between the presence of AGNs and the quenching of massive galaxies at <jats:italic>z</jats:italic> ∼ 2.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To study properties of magnetohydrodynamic (MHD) convection and resultant dynamo activities in proto-neutron stars (PNSs), we construct a “PNS in a box” simulation model and solve the compressible MHD equation coupled with a nuclear equation of state (EOS) and simplified leptonic transport. As a demonstration, we apply it to two types of PNS model with different internal structures: a fully convective model and a spherical-shell convection model. By varying the spin rate of the models, the rotational dependence of convection and the dynamo that operate inside the PNS is investigated. We find that, as a consequence of turbulent transport by rotating stratified convection, large-scale structures of flow and thermodynamic fields are developed in all models. Depending on the spin rate and the depth of the convection zone, various profiles of the large-scale structures are obtained, which can be physically understood as steady-state solutions to the “mean-field” equation of motion. Additionally to those hydrodynamic structures, a large-scale magnetic component of <jats:inline-formula> <jats:tex-math> <?CDATA ${ \mathcal O }({10}^{15})$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac34f6ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> G is also spontaneously organized in disordered tangled magnetic fields in all models. The higher the spin rate, the stronger the large-scale magnetic component grows. Intriguingly, as an overall trend, the fully convective models have a stronger large-scale magnetic component than that in the spherical-shell convection models. The deeper the convection zone extends, the larger the size of the convective eddies becomes. As a result, rotationally constrained convection seems to be more easily achieved in the fully convective model, resulting in a higher efficiency of the large-scale dynamo there. To gain a better understanding of the origin of the diversity of a neutron star’s magnetic field, we need to study the PNS dynamo in a wider parameter range.</jats:p>