Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Mass measurements and absorption-line studies indicate that the stellar initial mass function (IMF) is bottom-heavy in the central regions of many early-type galaxies, with an excess of low-mass stars compared to the IMF of the Milky Way. Here we test this hypothesis using a method that is independent of previous techniques. Low-mass stars have strong chromospheric activity characterized by nonthermal emission at short wavelengths. Approximately half of the UV flux of M dwarfs is contained in the <jats:italic>λ</jats:italic>1215.7 Ly<jats:italic>α</jats:italic> line, and we show that the total Ly<jats:italic>α</jats:italic> emission of an early-type galaxy is a sensitive probe of the IMF with a factor of ∼2 flux variation in response to plausible variations in the number of low-mass stars. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the Ly<jats:italic>α</jats:italic> line in the centers of the massive early-type galaxies NGC 1407 and NGC 2695. We detect Ly<jats:italic>α</jats:italic> emission in both galaxies and demonstrate that it originates in stars. We find that the Ly<jats:italic>α</jats:italic> to <jats:italic>i</jats:italic>-band flux ratio is a factor of 2.0 ± 0.4 higher in NGC 1407 than in NGC 2695, in agreement with the difference in their IMFs as previously determined from gravity-sensitive optical absorption lines. Although a larger sample of galaxies is required for definitive answers, these initial results support the hypothesis that the IMF is not universal but varies with environment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of candidate galaxy–absorber pairs for 43 low-redshift QSO sightlines (0.06 &lt; <jats:italic>z</jats:italic> &lt; 0.85) observed with the Hubble Space Telescope/Cosmic Origins Spectrograph that lie within the footprint of the Sloan Digital Sky Survey with a statistical approach to match absorbers with galaxies near the QSO lines of sight using only the SDSS Data Release 12 photometric data for the galaxies, including estimates of their redshifts. Our Bayesian methods combine the SDSS photometric information with measured properties of the circumgalactic medium to find the most probable galaxy match, if any, for each absorber in the line-of-sight QSO spectrum. We find ∼630 candidate galaxy–absorber pairs using two different statistics. The methods are able to reproduce pairs reported in the targeted spectroscopic studies upon which we base the statistics at a rate of 72%. The properties of the galaxies comprising the candidate pairs have median redshift, luminosity, and stellar mass, all estimated from the photometric data, <jats:italic>z</jats:italic> = 0.13, <jats:italic>L</jats:italic> = 0.1<jats:italic>L</jats:italic> <jats:sup>*</jats:sup>, and <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({M}_{* }/{M}_{\odot })=9.7$?> </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>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>9.7</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2954ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The median impact parameter of the candidate pairs is ∼430 kpc, or ∼3.5 times the galaxy virial radius. The results are broadly consistent with the high Ly<jats:italic>α</jats:italic> covering fraction out to this radius found in previous studies. This method of matching absorbers and galaxies can be used to prioritize targets for spectroscopic studies, and we present specific examples of promising systems for such follow-up.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is unclear whether successive filament eruptions at different sites within a short time interval are physically connected or not. Here, we present the observations of successive eruptions of a small and a large filament in a tripolar magnetic field region whose coronal magnetic field showed as a fan-spine magnetic system. By analyzing the multiwavelength observations taken by the Solar Dynamic Observatory and the extrapolated three-dimensional coronal magnetic field, we find that the two filaments resided respectively in the two lobes that make up the inner fan structure of the fan-spine magnetic system. In addition, a small fan-spine system was also revealed by the squashing factor Q map, which located in the east lobe of the fan structure of the large fan-spine system. The eruption of the small filament was a failed filament eruption, which did not cause any coronal mass ejection (CME) except for three flare ribbons and two post-flare-loop systems connecting the three magnetic polarities. The eruption of the large filament not only caused similar post-flare-loop systems and flare ribbons, as observed in the small filament eruption, but also a large-scale CME. Based on our analysis results, we conclude that the two successive filament eruptions were physically connected, in which the topology change caused by the small filament eruption is thought to be the physical linkage. In addition, the eruption of the small fan-spine structure further accelerated the instability and violent eruption of the large filament.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To figure out the effect of stellar mass and local environment on morphological transformation and star formation quenching in galaxies, we use the massive (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ≥ 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) galaxies at 0.5 ≤ <jats:italic>z</jats:italic> ≤ 2.5 in five fields of 3D-HST/CANDELS. Based on the <jats:italic>UVJ</jats:italic> diagnosis and the possibility of possessing a spheroid, our sample of massive galaxies is classified into four populations: quiescent early-type galaxies (qEs), quiescent late-type galaxies (qLs), star-forming early-type galaxies (sEs), and star-forming late-type galaxies (sLs). It is found that the quiescent fraction is significantly elevated at the high ends of mass and local environmental overdensity, which suggests a clear dependence of quenching on both mass and local environment. Over cosmic time, the mass dependence of galaxy quiescence decreases while the local environment dependence increases. The early-type fraction is found to be larger only at the high-mass end, indicating an evident mass dependence of morphological transformation. This mass dependence becomes more significant at lower redshifts. Among the four populations, the fraction of active galactic nuclei (AGNs) in the qLs peaks at 2 &lt; <jats:italic>z</jats:italic> ≤ 2.5, and rapidly declines with cosmic time. The sEs are found to have higher AGN fractions of 20%–30% at 0.5 ≤ <jats:italic>z</jats:italic> &lt; 2 . The redshift evolution of AGN fractions in the qLs and sEs suggests that AGN feedback could have played important roles in the formation of the qLs and sEs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Radioactive nuclei were present in the early solar system (ESS), as inferred from analysis of meteorites. Many are produced in massive stars, either during their lives or their final explosions. In the first paper of this series (Brinkman et al. 2019), we focused on the production of <jats:sup>26</jats:sup>Al in massive binaries. Here, we focus on the production of another two short-lived radioactive nuclei, <jats:sup>36</jats:sup>Cl and <jats:sup>41</jats:sup>Ca, and the comparison to the ESS data. We used the MESA stellar evolution code with an extended nuclear network and computed massive (10–80 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), rotating (with initial velocities of 150 and 300 km s<jats:sup>−1</jats:sup>) and nonrotating single stars at solar metallicity (<jats:italic>Z</jats:italic> = 0.014) up to the onset of core collapse. We present the wind yields for the radioactive isotopes <jats:sup>26</jats:sup>Al, <jats:sup>36</jats:sup>Cl, and <jats:sup>41</jats:sup>Ca, and the stable isotopes <jats:sup>19</jats:sup>F and <jats:sup>22</jats:sup>Ne. In relation to the stable isotopes, we find that only the most massive models, ≥60 and ≥40 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> give positive <jats:sup>19</jats:sup>F and <jats:sup>22</jats:sup>Ne yields, respectively, depending on the initial rotation rate. In relation to the radioactive isotopes, we find that the ESS abundances of <jats:sup>26</jats:sup>Al and <jats:sup>41</jats:sup>Ca can be matched with by models with initial masses ≥40 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, while <jats:sup>36</jats:sup>Cl is matched only by our most massive models, ≥60 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. <jats:sup>60</jats:sup>Fe is not significantly produced by any wind model, as required by the observations. Therefore, massive star winds are a favored candidate for the origin of the very short-lived <jats:sup>26</jats:sup>Al, <jats:sup>36</jats:sup>Cl, and <jats:sup>41</jats:sup>Ca in the ESS.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Through the Backyard Worlds: Planet 9 citizen science project we discovered a late-type L dwarf co-moving with the young K0 star BD+60 1417 at a projected separation of 37″ or 1662 au. The secondary—CWISER J124332.12+600126.2 (W1243)—is detected in both the CatWISE2020 and 2MASS reject tables. The photometric distance and CatWISE proper motion both match that of the primary within ∼1<jats:italic>σ</jats:italic> and our estimates for a chance alignment yield a zero probability. Follow-up near-infrared spectroscopy reveals W1243 to be a very red 2MASS (<jats:italic>J</jats:italic>–<jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> = 2.72), low surface gravity source that we classify as L6–L8<jats:italic>γ</jats:italic>. Its spectral morphology strongly resembles that of confirmed late-type L dwarfs in 10–150 Myr moving groups as well as that of planetary mass companions. The position on near- and mid-infrared color–magnitude diagrams indicates the source is redder and fainter than the field sequence, a telltale sign of an object with thick clouds and a complex atmosphere. For the primary we obtained new optical spectroscopy and analyzed all available literature information for youth indicators. We conclude that the Li <jats:sc>i</jats:sc> abundance, its loci on color–magnitude and color–color diagrams, and the rotation rate revealed in multiple TESS sectors are all consistent with an age of 50–150 Myr. Using our re-evaluated age of the primary and the Gaia parallax, along with the photometry and spectrum for W1243, we find <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> = 1303 ± 31 K, log <jats:italic>g</jats:italic> = 4.3 ± 0.17 cm s<jats:sup>−2</jats:sup>, and a mass of 15 ± 5 <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub>. We find a physical separation of ∼1662 au and a mass ratio of ∼0.01 for this system. Placing it in the context of the diverse collection of binary stars, brown dwarfs, and planetary companions, the BD+60 1417 system falls in a sparsely sampled area where the formation pathway is difficult to assess.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Big bang nucleosynthesis (BBN) is the standard model theory for the production of light nuclides during the early stages of the universe, taking place about 20 minutes after the big bang. Deuterium production, in particular, is highly sensitive to the primordial baryon density and the number of neutrino species, and its abundance serves as a sensitive test for the conditions in the early universe. The comparison of observed deuterium abundances with predicted ones requires reliable knowledge of the relevant thermonuclear reaction rates and their corresponding uncertainties. Recent observations reported the primordial deuterium abundance with percent accuracy, but some theoretical predictions based on BBN are in tension with the measured values because of uncertainties in the cross section of the deuterium-burning reactions. In this work, we analyze the <jats:italic>S</jats:italic>-factor of the D(p,<jats:italic>γ</jats:italic>)<jats:sup>3</jats:sup>He reaction using a hierarchical Bayesian model. We take into account the results of 11 experiments, spanning the period of 1955–2021, more than any other study. We also present results for two different fitting functions, a two-parameter function based on microscopic nuclear theory and a four-parameter polynomial. Our recommended reaction rates have a 2.2% uncertainty at 0.8 GK, which is the temperature most important for deuterium BBN. Differences between our rates and previous results are discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a census of neutral gas in the Milky Way disk and halo down to limiting column densities of <jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) ∼ 10<jats:sup>14</jats:sup> cm<jats:sup>−2</jats:sup> using measurements of H <jats:sc>i</jats:sc> Lyman series absorption from the Far Ultraviolet Spectroscopic Explorer. Our results are drawn from an analysis of 25 AGN sight lines spread evenly across the sky with Galactic latitude ∣<jats:italic>b</jats:italic>∣ ≳ 20°. By simultaneously fitting multi-component Voigt profiles to 11 Lyman series absorption transitions covered by FUSE (Ly<jats:italic>β</jats:italic>–Ly<jats:italic>μ</jats:italic>) plus HST measurements of Ly<jats:italic>α</jats:italic>, we derive the kinematics and column densities of a sample of 152 H <jats:sc>i</jats:sc> absorption components. While saturation prevents accurate measurements of many components with column densities 17 ≲ log <jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) ≲ 19, we derive robust measurements at log <jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) ≲ 17 and log <jats:italic>N</jats:italic>(H <jats:sc>i</jats:sc>) ≳ 19. We derive the first ultraviolet H <jats:sc>i</jats:sc> column density distribution function (CDDF) of the Milky Way, both globally and for low-velocity (ISM), intermediate-velocity clouds (IVCs), and high-velocity clouds (HVCs). We find that IVCs and HVCs show statistically indistinguishable CDDF slopes, with <jats:italic>β</jats:italic> <jats:sub>IVC</jats:sub> = <jats:inline-formula> <jats:tex-math> <?CDATA $-{1.01}_{-0.14}^{+0.15}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.01</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.15</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac1b9fieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:italic>β</jats:italic> <jats:sub>HVC</jats:sub> = <jats:inline-formula> <jats:tex-math> <?CDATA $-{1.05}_{-0.06}^{+0.07}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac1b9fieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Overall, the CDDF of the Galactic disk and halo appears shallower than that found by comparable extragalactic surveys, suggesting a relative abundance of high column density gas in the Galactic halo. We derive the sky-covering fractions as a function of H <jats:sc>i</jats:sc> column density, finding an enhancement of IVC gas in the northern hemisphere compared to the south. We also find evidence for an excess of inflowing H <jats:sc>i</jats:sc> over outflowing H <jats:sc>i</jats:sc>, with −0.88 ± 0.40 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> of HVC inflow versus ≈0.20 ± 0.10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> of HVC outflow, confirming an excess of inflowing HVCs seen in UV metal lines.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have been carrying out a dense monitoring of the blazar OJ 287 with Swift since late 2015 as part of our project MOMO (Multiwavelength Observations and Modeling of OJ 287). This is the densest existing monitoring of OJ 287 involving X-ray/UV data. In this latest publication of a sequence, we characterize the multiwavelength variability of OJ 287 based on &gt;4000 Swift single-wave-band data sets including archival data since 2005. A structure function analysis reveals a characteristic timescale of ∼5 days in the optical–UV at epochs of low-level activity and larger during outbursts. The discrete correlation function shows zero lag between optical and UV, with <jats:italic>τ</jats:italic> = 0 ± 1 day at the epoch of densest cadence. During outbursts (in 2016/17 and 2020) the X-rays follow the UV with near-zero lags. However, during quiescence, the delay is 7–18 days with X-rays leading or lagging, interpreted as due to a different X-ray component dominated by inverse Compton emission. Scaling relations are used to derive the characteristic length scales of the broad-line region and torus in OJ 287. A remarkable, symmetric UV–optical deep fade is identified in late 2017, lasting 2 months. We rule out occultation from the passage of a dusty cloud and a model where the secondary black hole deflects the jet between the primary and observer. We speculate about a temporary dispersion or jet swing event in the core or in a bright quasi-stationary jet feature. The deep fade reveals an additional, spatially distinct X-ray component. The epoch 2020.9–2021.1 was searched for precursor flare activity predicted by the binary black hole model of OJ 287.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Overshooting of turbulent motions from convective regions into adjacent stably stratified zones plays a significant role in stellar interior dynamics, as this process may lead to mixing of chemical species and contribute to the transport of angular momentum and magnetic fields. We present a series of fully nonlinear, three-dimensional (3D) anelastic simulations of overshooting convection in a spherical shell that are focused on the dependence of the overshooting dynamics on the density stratification and the rotation, both key ingredients in stars that however have not been studied systematically together via global simulations. We demonstrate that the overshoot lengthscale is not simply a monotonic function of the density stratification in the convective region, but instead it depends on the ratio of the density stratifications in the two zones. Additionally, we find that the overshoot lengthscale decreases with decreasing Rossby number Ro and scales as Ro<jats:sup>0.23</jats:sup> while it also depends on latitude with higher Rossby cases leading to a weaker latitudinal variation. We examine the mean flows arising due to rotation and find that they extend beyond the base of the convection zone into the stable region. Our findings may provide a better understanding of the dynamical interaction between stellar convective and radiative regions, and motivate future studies particularly related to the solar tachocline and the implications of its overlapping with the overshoot region.</jats:p>