Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Inspired by the excess soft X-ray emission recently detected in Green Pea galaxies, we model the soft X-ray emission (0.5–2.0 keV) of hot gas from star-cluster winds. By combining individual star clusters, we estimate the soft X-ray emission expected from the typically unresolved diffuse hot gas in starburst galaxies, devoid of competing emission from, e.g., active galactic nuclei (AGNs) or other unresolved point sources. We use stellar models of subsolar metallicities (0.02 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub> and 0.4 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>) and take into account supernova explosions for massive stars. For lower metallicities, we find that stellar winds do not contribute significantly (≲3% of the mechanical energy) to the observed soft X-ray emission of normal star-forming galaxies. For higher metallicities and possibly also for larger proportions of massive star clusters in the simulated starburst galaxies, we reproduce well the observed correlation between star formation rate and X-ray luminosity previously reported in the literature. However, we find that no combination of model assumptions is capable of reproducing the substantial soft X-ray emission observed from Green Pea galaxies, indicating that other emission mechanisms (i.e., unusually large quantities of high-/low-mass X-ray binaries, ultraluminous X-ray sources, a modified initial mass function, intermediate-mass black holes, or AGNs) are more likely to be responsible for the X-ray excess.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Chemical models predict that in cold cores gas-phase methanol is expected to be abundant at the outer edge of the CO depletion zone, where CO is actively adsorbed. CO adsorption correlates with volume density in cold cores, and, in nearby molecular clouds, catastrophic CO freeze-out happens at volume densities above 10<jats:sup>4</jats:sup> cm<jats:sup>−3</jats:sup>. The methanol production rate is maximized there and its freeze-out rate does not overcome its production rate, while the molecules are shielded from UV destruction by gas and dust. Thus, in cold cores, methanol abundance should generally correlate with visual extinction, which depends on both volume and column density. In this work, we test the most basic model prediction that maximum methanol abundance is associated with a <jats:italic>local</jats:italic> <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ∼ 4 mag in dense cores and constrain the model parameters with the observational data. With the IRAM 30 m antenna, we mapped the CH<jats:sub>3</jats:sub>OH (2–1) and (3–2) transitions toward seven dense cores in the L1495 filament in Taurus to measure the methanol abundance. We use the Herschel/SPIRE maps to estimate visual extinction, and the C<jats:sup>18</jats:sup>O(2–1) maps from Tafalla &amp; Hacar to estimate CO depletion. We explored the observed and modeled correlations between the methanol abundances, CO depletion, and visual extinction, varying the key model parameters. The modeling results show that hydrogen surface diffusion via tunneling is crucial to reproduce the observed methanol abundances, and the necessary reactive desorption efficiency matches the one deduced from laboratory experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the results of variability power spectral density (PSD) analysis using multiwavelength radio to GeV <jats:italic>γ</jats:italic>-ray light curves covering timescales of decades/years to days/minutes for the blazars 3C 279 and PKS 1510−089. The PSDs are modeled as single power laws, and the best-fit spectral shape is derived using the “power spectral response” method. With more than 10 yr of data obtained with weekly/daily sampling intervals, most of the PSDs cover ∼2–4 decades in temporal frequency; moreover, in the optical band, the PSDs cover ∼6 decades for 3C 279 due to the availability of intranight light curves. Our main results are the following: (1) on timescales ranging from decades to days, the synchrotron and the inverse-Compton spectral components, in general, exhibit red-noise (slope ∼2) and flicker-noise (slope ∼1) type variability, respectively; (2) the slopes of <jats:italic>γ</jats:italic>-ray variability PSDs obtained using a 3 hr integration bin and 3 weeks total duration exhibit a range between ∼1.4 and ∼2.0 (mean slope = 1.60 ± 0.70), consistent within errors with the slope on longer timescales; (3) comparisons of fractional variability indicate more power on timescales ≤100 days at <jats:italic>γ</jats:italic>-ray frequencies compared to longer wavelengths, in general (except between the <jats:italic>γ</jats:italic>-ray and optical wavelengths for PKS 1510−089); (4) the normalization of intranight optical PSDs for 3C 279 appears to be a simple extrapolation from longer timescales, indicating a continuous (single) process driving the variability at optical wavelengths; and (5) the emission at optical/infrared wavelengths may involve a combination of disk and jet processes for PKS 1510−089.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Comparing the inactive and gas-poor normal lenticular galaxies (S0s) in the local universe, we study a barred star-forming S0 galaxy, PGC 34107, which has been observed by the Centro Astronómico Hispano Alemán 3.5 m telescope and the Northern Extended Millimeter Array. The spatially resolved ionized gas and molecular gas traced by <jats:sup>12</jats:sup>CO(1–0), hereafter CO(1–0), show similar distribution and kinematics to the stellar component with an off-center star-forming region, ∼380 pc away from the center. The resolved kinematics of molecular CO(1–0) emission reveals that there is a blueshifted (redshifted) velocity component on the receding (approaching) side of the galaxy along the stellar bar. This might provide plausible evidence of noncircular motion, such as the bar-induced molecular gas inflow. The velocity of the molecular gas inflow decreases when approaching toward the peak of the off-center star formation in the north, which might be associated with the inner Lindblad resonance. In addition to CO(1–0), we also detect the isotopic line of <jats:sup>13</jats:sup>CO(1–0). For most H<jats:italic>α</jats:italic>, CO(1–0) and <jats:sup>13</jats:sup>CO(1–0) emissions are concentrated on this northern star-forming region. We find that PGC 34107 follows the local stellar mass–metallicity relation, star-forming main sequence, and the Kennicutt–Schmidt law. The resolved and integrated molecular gas main sequence suggests that there is a higher gas fraction in the central region of the galaxy, which supports a scenario that the bar-induced gas reservoir provides the raw material, and subsequently triggers the central star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of PSR J1555−2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. This fast and energetic (<jats:inline-formula> <jats:tex-math> <?CDATA $\dot{E}=3\times {10}^{35}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>35</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac49efieqn1.gif" xlink:type="simple" /> </jats:inline-formula> erg s<jats:sup>−1</jats:sup>) millisecond pulsar was first detected as a gamma-ray point source in Fermi Large Area Telescope (LAT) sky survey observations. Guided by a steep-spectrum radio point source in the Fermi error region, we performed a search at 820 MHz with the Green Bank Telescope that first discovered the pulsations. The initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the LAT data, from which we derive a timing solution valid for the full Fermi mission. In addition to the discovery and timing of radio and gamma-ray pulsations, we searched for X-ray pulsations using NICER but no significant pulsations were detected. We also obtained time-series <jats:italic>r</jats:italic>-band photometry that indicates strong heating of the companion star by the pulsar wind. Material blown off the heated companion eclipses the 820 MHz radio pulse during inferior conjunction of the companion for ≈10% of the orbit, which is twice the angle subtended by its Roche lobe in an edge-on system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The disk components of galaxies generally show an exponential profile extending over several scale lengths, both in mass and star formation rate, but the physical origin is not well understood. We explore a physical model in which the galactic gas disk is viewed as a “modified accretion disk” in which coplanar gas inflow, driven by viscous stresses in the disk, provides the fuel for star formation, which progressively removes gas as it flows inward. We show that magnetic stresses from magneto-rotational instability are the most plausible source of the required viscosity, and construct a simple physical model to explore this. A key feature is to link the magnetic field strength to the local star formation surface density, <jats:inline-formula> <jats:tex-math> <?CDATA ${B}_{\mathrm{tot}}\propto {{\rm{\Sigma }}}_{\mathrm{SFR}}^{\alpha }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>tot</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>SFR</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac49edieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. This provides a feedback loop between star formation and the flow of gas. We find that the model naturally produces stable steady-state exponential disks, as long as <jats:italic>α</jats:italic> ∼ 0.15, the value indicated from spatially resolved observations of nearby galaxies. The disk scale length <jats:italic>h</jats:italic> <jats:sub>R</jats:sub> is set by the rate at which the disk is fed, by the normalization of the <jats:italic>B</jats:italic> <jats:sub>tot</jats:sub>–Σ<jats:sub>SFR</jats:sub> relation and by the circular velocity of the halo. The angular momentum distribution of the gas and stars within the disk is a consequence of the transfer of angular momentum that is inherent to the operation of an accretion disk, rather than the initial angular momentum of the inflowing material. We suggest that magnetic stresses likely play a major role in establishing the stable exponential form of galactic disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The presence of complex organic molecules (COMs) in the interstellar medium is of great interest since it may link to the origin and prevalence of life in the universe. Aiming to investigate the occurrence of COMs and their possible origins, we conducted a chemical census toward a sample of protostellar cores as part of the Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps project. We report the detection of 11 hot corino sources, which exhibit compact emissions from warm and abundant COMs, among 56 Class 0/I protostellar cores. All of the hot corino sources discovered are likely Class 0, and their sizes of the warm region (&gt;100 K) are comparable to 100 au. The luminosity of the hot corino sources exhibits positive correlations with the total number of methanol and the extent of its emissions. Such correlations are consistent with the thermal desorption picture for the presence of hot corinos and suggest that the lower-luminosity (Class 0) sources likely have a smaller region with COM emissions. With the same sample selection method and detection criteria being applied, the detection rates of the warm methanol in the Orion cloud (15/37) and the Perseus cloud (28/50) are statistically similar when the cloud distances and the limited sample size are considered. Observing the same set of COM transitions will bring a more informative comparison between the cloud properties.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We used a convolutional neural network to infer stellar rotation periods from a set of synthetic light curves simulated with realistic spot-evolution patterns. We convolved these simulated light curves with real TESS light curves containing minimal intrinsic astrophysical variability to allow the network to learn TESS systematics and estimate rotation periods despite them. In addition to periods, we predict uncertainties via heteroskedastic regression to estimate the credibility of the period predictions. In the most credible half of the test data, we recover 10% accurate periods for 46% of the targets, and 20% accurate periods for 69% of the targets. Using our trained network, we successfully recover periods of real stars with literature rotation measurements, even past the 13.7 day limit generally encountered by TESS rotation searches using conventional period-finding techniques. Our method also demonstrates resistance to half-period aliases. We present the neural network and simulated training data, and introduce the software <jats:monospace>butterpy</jats:monospace> used to synthesize the light curves using realistic starspot evolution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Isotope variations of nucleosynthetic origin among solar system solid samples are well documented, yet the origin of these variations is still uncertain. The observed variability of <jats:sup>54</jats:sup>Cr among materials formed in different regions of the protoplanetary disk has been attributed to variable amounts of presolar, chromium-rich oxide (chromite) grains, which exist within the meteoritic stardust inventory and most likely originated from some type of supernova explosion. To investigate if core-collapse supernovae (CCSNe) could be the site of origin of these grains, we analyze yields of CCSN models of stars with initial masses 15, 20, and 25 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and solar metallicity. We present an extensive abundance data set of the Cr, Mg, and Al isotopes as a function of enclosed mass. We find cases in which the explosive C ashes produce a composition in good agreement with the observed <jats:sup>54</jats:sup>Cr/<jats:sup>52</jats:sup>Cr and <jats:sup>53</jats:sup>Cr/<jats:sup>52</jats:sup>Cr ratios as well as the <jats:sup>50</jats:sup>Cr/<jats:sup>52</jats:sup>Cr ratios. Taking into account that the signal at atomic mass 50 could also originate from <jats:sup>50</jats:sup>Ti, the ashes of explosive He burning also match the observed ratios. Addition of material from the He ashes (enriched in Al and Cr relative to Mg to simulate the make-up of chromite grains) to the solar system’s composition may reproduce the observed correlation between Mg and Cr anomalies, while material from the C ashes does not present significant Mg anomalies together with Cr isotopic variations. In all cases, nonradiogenic, stable Mg isotope variations dominate over the variations expected from <jats:sup>26</jats:sup>Al.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thirteen yr observation data of 4FGL J0824.9+3915 with the Large Area Telescope on board the Fermi Gamma Ray Space Telescope (Fermi/LAT) are analyzed for revisiting whether 4C +39.23B, a compact steep-spectrum (CSS) source close to a flat-spectrum radio quasar (FSRQ) 4C +39.23A in the <jats:italic>γ</jats:italic>-ray emitting region of 4FGL J0824.9+3915, is a <jats:italic>γ</jats:italic>-ray emitter. We find that the time-integrated <jats:italic>γ</jats:italic>-ray emission of 4FGL J0824.9+3915 is overwhelmingly dominated by 4C +39.23A. It shows significant variability at a 6.7<jats:italic>σ</jats:italic> confidence level and the average <jats:italic>γ</jats:italic>-ray flux in the 0.1–300 GeV energy band is (1.60 ± 0.15) × 10<jats:sup>−8</jats:sup> ph cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> with a power-law photon spectral index of 2.48 ± 0.05. During MJD 57500–58500, 4FGL J0824.9+3915 is in a low state with a steady <jats:italic>γ</jats:italic>-ray flux. Through the analysis of the Fermi/LAT observation data in this time interval, it is found that the test statistic values of the <jats:italic>γ</jats:italic>-ray emission from 4C +39.23A and 4C +39.23B are ∼5 and ∼31, respectively, indicating that the <jats:italic>γ</jats:italic>-ray emission in this time interval is dominated by CSS 4C +39.23B. The derived average flux in this time interval for 4C +39.23B is (9.40 ± 4.10) × 10<jats:sup>−9</jats:sup> ph cm <jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> with Γ<jats:sub> <jats:italic>γ</jats:italic> </jats:sub> = 2.45 ± 0.17. Attributing the spectral energy distribution (SED) of 4C +39.23B to the radiations from its core and extended region, we show that the SED can be represented with a two-zone leptonic model. Its <jats:italic>γ</jats:italic>-ray emission is contributed to by the core region. The derived magnetic field strength and Doppler boosting factor of the core are 0.13 G and 6.5. Comparing 4C +39.23B with other <jats:italic>γ</jats:italic>-emitting CSSs and compact symmetric objects (CSOs) in the Γ<jats:sub> <jats:italic>γ</jats:italic> </jats:sub> − <jats:italic>L</jats:italic> <jats:sub> <jats:italic>γ</jats:italic> </jats:sub> plane, it resembles CSSs.</jats:p>