Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The toroidal magnetic field is assumed to be generated in the tachocline in most Babcock–Leighton (BL)-type solar dynamo models, in which the poloidal field is produced by the emergence and subsequent dispersal of sunspot groups. However, magnetic activity of fully convective stars and MHD simulations of global stellar convection have recently raised serious doubts regarding the importance of the tachocline in the generation of the toroidal field. In this study, we aim to develop a new BL-type dynamo model, in which the dynamo operates mainly within the bulk of the convection zone. Our 2D model includes the effect of solar-like differential rotation, one-cell meridional flow, near-surface radial pumping, strong turbulent diffusion, BL-type poloidal source, and nonlinear back-reaction of the magnetic field on its source with a vertical outer boundary condition. The model leads to a simple dipolar configuration of the poloidal field that has the dominant latitudinal component, which is wound up by the latitudinal shear within the bulk of the convection zone to generate the toroidal flux. As a result, the tachocline plays a negligible role in the model. The model reproduces the basic properties of the solar cycle, including (a) approximately 11 yr cycle period and 18 yr extended cycle period; (b) equatorward propagation of the antisymmetric toroidal field starting from high latitudes; and (c) polar field evolution that is consistent with observations. Our model opens the possibility for a paradigm shift in understanding the solar cycle to transition from the classical flux transport dynamo.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use IllustrisTNG simulations to explore the dynamic scaling relation between massive clusters and their—central—brightest cluster galaxies (BCGs). The IllustrisTNG-300 simulation we use includes 280 massive clusters from the <jats:italic>z</jats:italic> = 0 snapshot with <jats:italic>M</jats:italic> <jats:sub>200</jats:sub> &gt; 10<jats:sup>14</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, enabling a robust statistical analysis. We derive the line-of-sight velocity dispersion of the stellar particles of the BCGs (<jats:italic>σ</jats:italic> <jats:sub>*,BCG</jats:sub>), analogous to the observed BCG stellar velocity dispersion. We also compute the subhalo velocity dispersion to measure the cluster velocity dispersion (<jats:italic>σ</jats:italic> <jats:sub>cl</jats:sub>). Both <jats:italic>σ</jats:italic> <jats:sub>*,BCG</jats:sub> and <jats:italic>σ</jats:italic> <jats:sub>cl</jats:sub> are proportional to the cluster halo mass, but the slopes differ slightly. Thus, like the observed relation, <jats:italic>σ</jats:italic> <jats:sub>*,BCG</jats:sub>/<jats:italic>σ</jats:italic> <jats:sub>cl</jats:sub> declines as a function of <jats:italic>σ</jats:italic> <jats:sub>cl</jats:sub>, but the scatter is large. We explore the redshift evolution of the <jats:italic>σ</jats:italic> <jats:sub>*,BCG</jats:sub> − <jats:italic>σ</jats:italic> <jats:sub>cl</jats:sub> scaling relation for <jats:italic>z</jats:italic> ≲ 1 in a way that can be compared directly with observations. The scaling relation has a similar slope at high redshift, but the scatter increases because of the large scatter in <jats:italic>σ</jats:italic> <jats:sub>*,BCG</jats:sub>. The simulations imply that high-redshift BCGs are dynamically more complex than their low-redshift counterparts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A quantitative data-driven comparison among supernovae (SNe) based on their spectral time series combined with multiband photometry is presented. We use an unsupervised random forest algorithm as a metric on a set of 82 well-documented SNe representing all the main spectroscopic types, in order to embed these in an abstract metric space reflecting shared correlations between the objects. We visualize the resulting metric space in 3D, revealing strong agreement with the current spectroscopic classification scheme. The embedding splits Type Ib supernovae into two groups, with one subgroup exhibiting broader, less prominent, higher-velocity lines than the other, possibly suggesting a new SN Ib subclass is required. The method could be to classify newly discovered SNe according to their distance from known event groups, or ultimately to devise a new, spectral–temporal classification scheme. Such an embedding could also depend on hidden parameters that may perhaps be physically interpretable.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical imaging and spectroscopy of SN 2018lfe, which we classify as a Type I superluminous supernova (SLSN-I) at a redshift of <jats:italic>z</jats:italic> = 0.3501 ± 0.0004 with a peak absolute magnitude of <jats:italic>M</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> = −22.1 ± 0.1 mag, one of the brightest SLSNe discovered. SN 2018lfe was identified for follow-up using our FLEET machine-learning pipeline. Both the light curve and the spectra of SN 2018lfe are consistent with the broad population of SLSNe. We fit the light curve with a magnetar central engine model and find an ejecta mass of <jats:italic>M</jats:italic> <jats:sub>ej</jats:sub> ≈ 3.8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, a magnetar spin period of <jats:italic>P</jats:italic> ≈ 2.9 ms, and a magnetic field strength of <jats:italic>B</jats:italic> <jats:sub>⊥</jats:sub> ≈ 2.8 × 10<jats:sup>14</jats:sup> G. The magnetic field strength is near the top of the distribution for SLSNe, while the spin period and ejecta mass are near the median values of the distribution for SLSNe. From late-time imaging and spectroscopy we find that the host galaxy of SN 2018lfe has an absolute magnitude of <jats:italic>M</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> = −17.85 ± 0.24, (<jats:italic>L</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub> = 0.029 ± 0.007<jats:italic>L</jats:italic>*), and an inferred metallicity of <jats:italic>Z</jats:italic> ≈ 0.3 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub> and star formation rate of ≈0.8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A complete census of dusty star-forming galaxies (DSFGs) at early epochs is necessary to constrain the obscured contribution to the cosmic star formation rate density (CSFRD); however, DSFGs beyond <jats:italic>z</jats:italic> ∼ 4 are both rare and hard to identify from photometric data alone due to degeneracies in submillimeter photometry with redshift. Here, we present a pilot study obtaining follow-up Atacama Large Millimeter Array (ALMA) 2 mm observations of a complete sample of 39 850 <jats:italic>μ</jats:italic>m-bright dusty galaxies in the SSA22 field. Empirical modeling suggests 2 mm imaging of existing samples of DSFGs selected at 850 <jats:italic>μ</jats:italic>m—1 mm can quickly and easily isolate the “needle in a haystack” DSFGs that sit at <jats:italic>z</jats:italic> &gt; 4 or beyond. Combining archival submillimeter imaging with our measured ALMA 2 mm photometry (1<jats:italic>σ</jats:italic> ∼ 0.08 mJy beam<jats:sup>−1</jats:sup> rms), we characterize the galaxies’ IR spectral energy distributions (SEDs) and use them to constrain redshifts. With available redshift constraints fit via the combination of six submillimeter bands, we identify 6/39 high-<jats:italic>z</jats:italic> candidates each with &gt;50% likelihood to sit at <jats:italic>z</jats:italic> &gt; 4, and find a positive correlation between redshift and 2 mm flux density. Specifically, our models suggest the addition of 2 mm to a moderately constrained IR SED will improve the accuracy of a millimeter-derived redshift from Δ<jats:italic>z</jats:italic>/(1 + <jats:italic>z</jats:italic>) = 0.3 to Δ<jats:italic>z</jats:italic>/(1 + <jats:italic>z</jats:italic>) = 0.2. Our IR SED characterizations provide evidence for relatively high-emissivity spectral indices (〈<jats:italic>β</jats:italic>〉 = 2.4 ± 0.3) in the sample. We measure that especially bright (<jats:italic>S</jats:italic> <jats:sub>850<jats:italic>μ</jats:italic> <jats:italic>m</jats:italic> </jats:sub> &gt; 5.55 mJy) DSFGs contribute ∼10% to the cosmic-averaged CSFRD from 2 &lt; <jats:italic>z</jats:italic> &lt; 5, confirming findings from previous work with similar samples.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this study, 36 cores (30 starless and six protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in the <jats:italic>J</jats:italic> = 1 → 0 transitions of HCO<jats:sup>+</jats:sup>, H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup>, N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup>, HNC, and HN<jats:sup>13</jats:sup>C. The asymmetry parameter <jats:italic>δV</jats:italic>, which was the ratio of the difference between the HCO<jats:sup>+</jats:sup> and H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> peak velocities to the H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores surveyed) were identified as cores with blue-skewed line profiles (asymmetric profiles with more intense blueshifted emission), and another two starless cores (7%) were identified as candidate blue-skewed line profiles. The peak velocity difference between HCO<jats:sup>+</jats:sup> and H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> of them was up to 0.9 km s<jats:sup>−1</jats:sup>, suggesting that some inward motions exceeded the speed of sound for the quiescent gas (∼10–17 K). The mean of <jats:italic>δV</jats:italic> of the five aforementioned starless cores was derived to be −0.5 ± 0.3. One core, G211.16−19.33North3, observed using the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array in DCO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 3 → 2 exhibited blue-skewed features. Velocity offset in the blue-skewed line profile with a dip in the DCO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 3 → 2 line was larger (∼0.5 km s<jats:sup>−1</jats:sup>) than that in HCO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 1 → 0 (∼0.2 km s<jats:sup>−1</jats:sup>), which may represent gravitational acceleration of inward motions. It seems that this core is at the last stage in the starless phase, judging from the chemical evolution factor version 2.0 (CEF2.0).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The physical characteristics and atmospheric chemical composition of newly discovered exoplanets are often inferred from their transit spectra, which are obtained from complex numerical models of radiative transfer. Alternatively, simple analytical expressions provide insightful physical intuition into the relevant atmospheric processes. The deep-learning revolution has opened the door for deriving such analytical results directly with a computer algorithm fitting to the data. As a proof of concept, we successfully demonstrate the use of symbolic regression on synthetic data for the transit radii of generic hot-Jupiter exoplanets to derive a corresponding analytical formula. As a preprocessing step, we use dimensional analysis to identify the relevant dimensionless combinations of variables and reduce the number of independent inputs, which improves the performance of the symbolic regression. The dimensional analysis also allowed us to mathematically derive and properly parameterize the most general family of degeneracies among the input atmospheric parameters that affect the characterization of an exoplanet atmosphere through transit spectroscopy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Being able to distinguish between galaxies that have recently undergone major-merger events, or are experiencing intense star formation, is crucial for making progress in our understanding of the formation and evolution of galaxies. As such, we have developed a machine-learning framework based on a convolutional neural network to separate star-forming galaxies from post-mergers using a data set of 160,000 simulated images from IllustrisTNG100 that resemble observed deep imaging of galaxies with Hubble. We improve upon previous methods of machine learning with imaging by developing a new approach to deal with the complexities of contamination from neighboring sources in crowded fields and define a quality control limit based on overlapping sources and background flux. Our pipeline successfully separates post-mergers from star-forming galaxies in IllustrisTNG 80% of the time, which is an improvement by at least 25% in comparison to a classification using the asymmetry (<jats:italic>A</jats:italic>) of the galaxy. Compared with measured Sérsic profiles, we show that star-forming galaxies in the CANDELS fields are predominantly disk-dominated systems while post-mergers show distributions of transitioning disks to bulge-dominated galaxies. With these new measurements, we trace the rate of post-mergers among asymmetric galaxies in the universe, finding an increase from 20% at <jats:italic>z</jats:italic> = 0.5 to 50% at <jats:italic>z</jats:italic> = 2. Additionally, we do not find strong evidence that the scattering above the star-forming main sequence can be attributed to major post-mergers. Finally, we use our new approach to update our previous measurements of galaxy merger rates <jats:inline-formula> <jats:tex-math> <?CDATA ${ \mathcal R }=0.022\pm 0.006\times {(1+z)}^{2.71\pm 0.31}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.022</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.006</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>z</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>2.71</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.31</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac66eaieqn1.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present spectroscopic and photometric observations of the Type IIP supernova, SN 2020jfo, in ultraviolet and optical wavelengths. SN 2020jfo occurred in the spiral galaxy M61 (NGC 4303), with eight observed supernovae in the past 100 yr. SN 2020jfo exhibited a short plateau lasting &lt; 65 days, and achieved a maximum brightness in <jats:italic>V</jats:italic>band of <jats:italic>M</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> = −17.4 ± 0.4 mag at about 8.0 ± 0.5 days since explosion. From the bolometric light curve, we have estimated the mass of <jats:sup>56</jats:sup>Ni synthesized in the explosion to be 0.033 ± 0.006 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The observed spectral features are typical for a Type IIP supernova except for shallow H<jats:italic>α</jats:italic> absorption throughout the evolution and the presence of stable <jats:sup>58</jats:sup>Ni feature at 7378 Å, in the nebular phase. Using hydrodynamical modeling in the <jats:monospace>MESA</jats:monospace> <jats:monospace>+</jats:monospace> <jats:monospace>STELLA</jats:monospace> framework, an ejecta mass of ∼5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> is estimated. Models also indicate SN 2020jfo could be the result of a red supergiant progenitor with <jats:italic>M</jats:italic> <jats:sub>ZAMS</jats:sub> ∼ 12 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Bolometric light-curve modeling revealed the presence of a secondary radiation source for initial ∼20 days, which has been attributed to interaction with a circumstellar material of mass ∼ 0.2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which most likely was ejected due to enhanced mass loss about 20 yr prior to the supernova explosion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a spectroscopic analysis of the most rapidly rotating stars currently known, VFTS 102 (<jats:inline-formula> <jats:tex-math> <?CDATA ${v}_{e}\sin i=649\pm 52$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:mn>649</mml:mn> <mml:mo>±</mml:mo> <mml:mn>52</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac66e6ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>; O9: Vnnne+) and VFTS 285 (<jats:inline-formula> <jats:tex-math> <?CDATA ${v}_{e}\sin i=610\pm 41$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:mn>610</mml:mn> <mml:mo>±</mml:mo> <mml:mn>41</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac66e6ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>; O7.5: Vnnn), both members of the 30 Dor complex in the Large Magellanic Cloud. This study is based on high-resolution ultraviolet spectra from Hubble Space Telescope/Cosmic Origins Spectrograph and optical spectra from the Very Large Telescope (VLT) X-shooter plus archival VLT GIRAFFE spectra. We utilize numerical simulations of their photospheres, rotationally distorted shape, and gravity darkening to calculate model spectral line profiles and predicted monochromatic absolute fluxes. We use a guided grid search to investigate parameters that yield best fits for the observed features and fluxes. These fits produce estimates of the physical parameters for these stars (plus a Galactic counterpart, <jats:italic>ζ</jats:italic> Oph) including the equatorial rotational velocity, inclination, radius, mass, gravity, temperature, and reddening. We find that both stars appear to be radial-velocity constant. VFTS 102 is rotating at critical velocity, has a modest He enrichment, and appears to share the motion of the nearby OB-association LH 99. These properties suggest that the star was spun up through a close binary merger. VFTS 285 is rotating at 95% of critical velocity, has a strong He enrichment, and is moving away from the R136 cluster at the center of 30 Dor. It is mostly likely a runaway star ejected by a supernova explosion that released the components of the natal binary system.</jats:p>