Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212–272 GHz) covers potential [C <jats:sc>ii</jats:sc>] emission in galaxies at 6 ≤ <jats:italic>z</jats:italic> ≤ 8 throughout a 2.9 arcmin<jats:sup>2</jats:sup> area. By selecting on known Ly<jats:italic>α</jats:italic> emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5<jats:italic>σ</jats:italic> [C <jats:sc>ii</jats:sc>] luminosity depth <jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>II</jats:sc>]</jats:sub> ∼ 2.0 × 10<jats:sup>8</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>, corresponding roughly to star formation rates (SFRs) of 10–20 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [C <jats:sc>ii</jats:sc>] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of <jats:italic>z</jats:italic> = 6–7 LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between <jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>ii</jats:sc>]</jats:sub> and SFR—with the exception of a single [C <jats:sc>ii</jats:sc>]-deficient, UV-luminous LBG. We also perform a blind search for [C <jats:sc>ii</jats:sc>]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [C <jats:sc>ii</jats:sc>] sources with <jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>II</jats:sc>]</jats:sub> &gt; 2.0 × 10<jats:sup>8</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub> (5<jats:italic>σ</jats:italic>) to be less than 1.8 × 10<jats:sup>−4</jats:sup> Mpc<jats:sup>−3</jats:sup> (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [C <jats:sc>ii</jats:sc>] luminosity function from <jats:italic>z</jats:italic> = 6–8 to <jats:italic>z</jats:italic> ∼ 0 by comparing the ASPECS measurement to literature results at lower redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A pair of nonthermal radio bubbles recently discovered in the inner few hundred parsecs of the Galactic center bears a close spatial association with elongated, thermal X-ray features called the X-ray chimneys. While their morphology, position, and orientation vividly point to an outflow from the Galactic center, the physical processes responsible for the outflow remain to be understood. We use 3D magnetohydrodynamic simulations to test the hypothesis that the radio bubbles/X-ray chimneys are the manifestation of an energetic outflow driven by multiple core-collapsed supernovae (SNe) in the nuclear stellar disk, where numerous massive stars are known to be present. Our simulations are run with different combinations of two main parameters, the supernova birth rate and the strength of a global magnetic field being vertically oriented with respect to the disk. The simulation results show that a hot gas outflow can naturally form and acquire a vertically elongated shape due to collimation by the magnetic pressure. In particular, the simulation with an initial magnetic field strength of 80 <jats:italic>μ</jats:italic>G and a supernova rate of 1 kyr<jats:sup>−1</jats:sup> can well reproduce the observed morphology, internal energy, and X-ray luminosity of the bubbles after an evolutionary time of 330 kyr. On the other hand, a magnetic field strength of 200 <jats:italic>μ</jats:italic>G gives rise to an overly elongated outflow that is inconsistent with the observed bubbles. The simulations also reveal that, inside the bubbles, mutual collisions between the shock waves of individual SNe produce dense filaments of locally amplified magnetic field. Such filaments may account for a fraction of the synchrotron-emitting radio filaments known to exist in the Galactic center.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present simultaneous measurements of emission from dust continuum at 230 GHz and the <jats:italic>J</jats:italic> = 2–1 <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, and C<jats:sup>18</jats:sup>O isotopologues at ∼15 pc resolution from individual giant molecular clouds (GMCs) in the Andromeda galaxy (M31). These observations were obtained in an ongoing survey of this galaxy being conducted with the Submillimeter Array. Initial results describing the continuum and <jats:sup>12</jats:sup>CO emission have been published earlier. Here, we primarily analyze the observations of <jats:sup>13</jats:sup>CO and C<jats:sup>18</jats:sup>O emission and compare them to the measurements of dust continuum and <jats:sup>12</jats:sup>CO emission. We also report additional dust continuum and CO measurements from newly added GMCs to the M31 sample. We detect spatially resolved <jats:sup>13</jats:sup>CO emission with high signal-to-noise ratios in 31 objects. We find the extent of the <jats:sup>13</jats:sup>CO emission to be nearly comparable to that of <jats:sup>12</jats:sup>CO, typically covering 75% of the area of the <jats:sup>12</jats:sup>CO emission. We derive <jats:sup>13</jats:sup>CO and C<jats:sup>18</jats:sup>O abundances of 2.9 × 10<jats:sup>−6</jats:sup> and 4.4 × 10<jats:sup>−7</jats:sup> relative to H<jats:sub>2</jats:sub>, respectively, by comparison with hydrogen column densities of the same regions derived from the dust continuum observations assuming a Milky Way gas-to-dust ratio. We find the isotopic abundance ratio [<jats:sup>13</jats:sup>CO]/[C<jats:sup>18</jats:sup>O] = 6.7 ± 2.9 to be consistent with the Milky Way value (8.1). Finally, we derive the mass-to-light conversion factors for all three CO species to be <jats:italic>α</jats:italic> <jats:sub>12</jats:sub> = 8.7 ± 3.9, <jats:italic>α</jats:italic> <jats:sub>13</jats:sub> = 48.9 ± 20.4, and <jats:inline-formula> <jats:tex-math> <?CDATA ${\alpha }_{18}={345}_{-31}^{+25}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe629ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <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> for the <jats:italic>J</jats:italic> = 2–1 transitions of <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, and C<jats:sup>18</jats:sup>O, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Light curves produced by the Kepler mission demonstrate stochastic brightness fluctuations (or <jats:italic>flicker</jats:italic>) of stellar origin which contribute to the noise floor, limiting the sensitivity of exoplanet detection and characterization methods. In stars with surface convection, the primary driver of these variations on short (sub-eight-hour) timescales is believed to be convective granulation. In this work, we improve existing models of this granular flicker amplitude, or <jats:italic>F</jats:italic> <jats:sub>8</jats:sub>, by including the effect of the Kepler bandpass on measured flicker, by incorporating metallicity in determining convective Mach numbers, and by using scaling relations from a wider set of numerical simulations. To motivate and validate these changes, we use a recent database of convective flicker measurements in Kepler stars, which allows us to more fully detail the remaining model-prediction error. Our model improvements reduce the typical misprediction of flicker amplitude from a factor of 2.5–2. We rule out rotation period and strong magnetic activity as possible explanations for the remaining model error, and we show that binary companions may affect convective flicker. We also introduce an <jats:italic>envelope</jats:italic> model that predicts a range of flicker amplitudes for any one star to account for some of the spread in numerical simulations, and we find that this range covers 78% of observed stars. We note that the solar granular flicker amplitude is lower than most Sun-like stars. This improved model of convective flicker amplitude can better characterize this source of noise in exoplanet studies as well as better inform models and simulations of stellar granulation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The prediction of the equation of state of hot, dense nuclear matter is one of the most complicated and interesting problems in nuclear astrophysics. At the same time, knowledge of it is the basic ingredient for some of the most interesting studies. In the present work, we concentrate our study on the construction of the equation of state of hot, dense nuclear matter, related mainly to the interior of the neutron star. We employ a theoretical nuclear model, which includes momentum-dependent interaction among the nucleons, along with state-of-the-art microscopic calculations. Thermal effects are introduced in a self-consistent way, and a set of isothermal and isentropic equations of state are predicted. The predicted equations of state are used in order to acquire and extend the knowledge of the thermal effect on both nonrotating and rapidly rotating with the Kepler frequency neutron stars. The simultaneous study of thermal and rotation effects provides useful information on some of the most important quantities, including the mass (gravitational and baryon) and radius, the Kepler frequency and Kerr parameter, the moment of inertia, etc. These quantities are directly related to studies of protoneutron stars and mainly the hot and rapidly rotating remnant of a binary neutron star merger. Data from the late observations of binary neutron star mergers and the present study may offer useful tools for investigation and help in providing possible constraints on the equation of state of nuclear matter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze light curves of 284,834 unique K2 targets using a Gaussian process model with a quasi-periodic kernel function. By cross-matching K2 stars to observations from Gaia Data Release 2, we have identified 69,627 likely main-sequence stars. From these we select a subsample of 8977 stars on the main sequence with highly precise rotation period measurements. With this sample we recover the gap in the rotation period−color diagram first reported by McQuillan et al. While the gap was tentatively detected in Reinhold &amp; Hekker, this work represents the first robust detection of the gap in K2 data for field stars. This is significant because K2 observed along many lines of sight at wide angular separation, in contrast to Kepler’s single line of sight. Together with recent results for rotation in open clusters, we interpret this gap as evidence for a departure from the <jats:italic>t</jats:italic> <jats:sup>−1/2</jats:sup> Skumanich spin-down law, rather than an indication of a bimodal star formation history. We provide maximum likelihood estimates and uncertainties for all parameters of the quasi-periodic light-curve model for each of the 284,834 stars in our sample.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the spectral diversity of Type Ia supernovae (SNe Ia) at maximum light using high signal-to-noise spectrophotometry of 173 SNe Ia from the Nearby Supernova Factory. We decompose the diversity of these spectra into different extrinsic and intrinsic components, and we construct a nonlinear parameterization of the intrinsic diversity of SNe Ia that preserves pairings of “twin” SNe Ia. We call this parameterization the “Twins Embedding.” Our methodology naturally handles highly nonlinear variability in spectra, such as changes in the photosphere expansion velocity, and uses the full spectrum rather than being limited to specific spectral line strengths, ratios, or velocities. We find that the time evolution of SNe Ia near maximum light is remarkably similar, with 84.6% of the variance in common to all SNe Ia. After correcting for brightness and color, the intrinsic variability of SNe Ia is mostly restricted to specific spectral lines, and we find intrinsic dispersions as low as ∼0.02 mag between 6600 and 7200 Å. With a nonlinear three-dimensional model plus one dimension for color, we can explain 89.2% of the intrinsic diversity in our sample of SNe Ia, which includes several different kinds of “peculiar” SNe Ia. A linear model requires seven dimensions to explain a comparable fraction of the intrinsic diversity. We show how a wide range of previously established indicators of diversity in SNe Ia can be recovered from the Twins Embedding. In a companion article, we discuss how these results can be applied to the standardization of SNe Ia for cosmology.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Effective spectroscopic diagnostics rely on the ability to convert a particular flux measurement into a physical interpretation. Knowledge of uncertainty is a central component of diagnostics. We present data from a simulated solar-like chromosphere, where we have addressed the question of whether degeneracy is a problem in mapping from a non-LTE chromospheric line profile to a particular vertical stratification of atmospheric properties along the line of sight. Our results indicate that stratification degeneracies do exist, at least in our simulated atmosphere. We quantify this effect through the creation of posterior densities for atmospheric properties based on the Mg <jats:sc>ii</jats:sc> h line profile using the approximate Bayesian computation (ABC) technique. We find that the predictive power of the ABC temperature posterior systematically varies as a function of atmospheric column mass and ground-truth temperature. The ABC posteriors more effectively reproduce the spectral intensity in the Ca <jats:sc>ii</jats:sc> 8542 Å line than they do temperature stratification, although residual error in the Ca <jats:sc>ii</jats:sc> line core is common. Our results illustrate that some degeneracies should be alleviated through simultaneous analysis of multiple chromospheric lines.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show how spectra of Type Ia supernovae (SNe Ia) at maximum light can be used to improve cosmological distance estimates. In a companion article, we used manifold learning to build a three-dimensional parameterization of the intrinsic diversity of SNe Ia at maximum light that we call the “Twins Embedding.” In this article, we discuss how the Twins Embedding can be used to improve the standardization of SNe Ia. With a single spectrophotometrically calibrated spectrum near maximum light, we can standardize our sample of SNe Ia with an rms of 0.101 ± 0.007 mag, which corresponds to 0.084 ± 0.009 mag if peculiar velocity contributions are removed and to 0.073 ± 0.008 mag if a larger reference sample were obtained. Our techniques can standardize the full range of SNe Ia, including those typically labeled as peculiar and often rejected from other analyses. We find that traditional light-curve width + color standardization such as SALT2 is not sufficient. The Twins Embedding identifies a subset of SNe Ia, including, but not limited to, 91T-like SNe Ia whose SALT2 distance estimates are biased by 0.229 ± 0.045 mag. Standardization using the Twins Embedding also significantly decreases host-galaxy correlations. We recover a host mass step of 0.040 ± 0.020 mag compared to 0.092 ± 0.026 mag for SALT2 standardization on the same sample of SNe Ia. These biases in traditional standardization methods could significantly impact future cosmology analyses if not properly taken into account.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stellar evolution and numerical hydrodynamics simulations depend critically on access to fast, accurate, thermodynamically consistent equations of state. We present Skye, a new equation of state for fully ionized matter. Skye includes the effects of positrons, relativity, electron degeneracy, Coulomb interactions, nonlinear mixing effects, and quantum corrections. Skye determines the point of Coulomb crystallization in a self-consistent manner, accounting for mixing and composition effects automatically. A defining feature of this equation of state is that it uses analytic free energy terms and provides thermodynamic quantities using automatic differentiation machinery. Because of this, Skye is easily extended to include new effects by simply writing new terms in the free energy. We also introduce a novel <jats:italic>thermodynamic extrapolation</jats:italic> scheme for extending analytic fits to the free energy beyond the range of the fitting data while preserving desirable properties like positive entropy and sound speed. We demonstrate Skye in action in the <jats:monospace>MESA</jats:monospace> stellar evolution software instrument by computing white dwarf cooling curves.</jats:p>