Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The largest moon of Neptune, Triton, possesses a cold and hazy atmosphere. Since the discovery of the near-surface haze layer during the Voyager fly in 1989, the haze formation mechanism has not been investigated in detail. Here we provide the first haze microphysical model on Triton. Our model solves the evolution of both size and porosity distributions of haze particles in a self-consistent manner. We simulated the formation of sphere and aggregate hazes with and without condensation of the C<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub> ice. The haze particles can grow into fractal aggregates with mass-equivalent sphere sizes of ∼0.1–1 <jats:italic>μ</jats:italic>m and fractal dimensions of <jats:italic>D</jats:italic> <jats:sub>f</jats:sub> = 1.8–2.2. The ice-free hazes cannot simultaneously explain both UV and visible observations of Voyager 2, while including the condensation of C<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub> ices provides two better solutions. For ice aggregates, the required total haze mass flux is ∼2 × 10<jats:sup>−15</jats:sup> g cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>. For the icy sphere scenario, the column-integrated C<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub> production rate is ∼8 × 10<jats:sup>−15</jats:sup> g cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, and the ice-free mass flux is ∼6 × 10<jats:sup>−17</jats:sup> g cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>. The UV occultation observations at short wavelengths, &lt;0.15 <jats:italic>μ</jats:italic>m, may slightly favor the icy aggregates. Observations of the haze optical depth and the degree of forward scattering in UV and visible should be able to distinguish whether Triton’s hazes are icy spheres or ice aggregates in future Triton missions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Cepheid period–luminosity (PL) relation is the key tool for measuring astronomical distances and for establishing the extragalactic distance scale. In particular, the local value of the Hubble constant (<jats:italic>H</jats:italic> <jats:sub>0</jats:sub>) strongly depends on Cepheid distance measurements. The recent Gaia Data Releases and other parallax measurements from the Hubble Space Telescope (HST) already enabled us to improve the accuracy of the slope (<jats:italic>α</jats:italic>) and intercept (<jats:italic>β</jats:italic>) of the PL relation. However, the dependence of this law on metallicity is still largely debated. In this paper, we combine three samples of Cepheids in the Milky Way (MW), the Large Magellanic Cloud (LMC), and the Small Magellanic Cloud (SMC) in order to derive the metallicity term (hereafter <jats:italic>γ</jats:italic>) of the PL relation. The recent publication of extremely precise LMC and SMC distances based on late-type detached eclipsing binary systems provides a solid anchor for the Magellanic Clouds. In the MW, we adopt Cepheid parallaxes from the early third Gaia Data Release. We derive the metallicity effect in <jats:italic>V</jats:italic>, <jats:italic>I</jats:italic>, <jats:italic>J</jats:italic>, <jats:italic>H</jats:italic>, <jats:italic>K</jats:italic> <jats:sub> <jats:italic>S</jats:italic> </jats:sub>, <jats:italic>W</jats:italic> <jats:sub> <jats:italic>VI</jats:italic> </jats:sub>, and <jats:italic>W</jats:italic> <jats:sub> <jats:italic>JK</jats:italic> </jats:sub>. In the <jats:italic>K</jats:italic> <jats:sub> <jats:italic>S</jats:italic> </jats:sub> band we report a metallicity effect of −0.221 ± 0.051 mag dex<jats:sup>−1</jats:sup>, the negative sign meaning that more metal-rich Cepheids are intrinsically brighter than their more metal-poor counterparts of the same pulsation period.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present new high-resolution (<jats:italic>R</jats:italic> = <jats:italic>λ</jats:italic>/Δ<jats:italic>λ</jats:italic> ∼ 14,000) spectra of the two brightest He <jats:sc>ii</jats:sc>-transparent quasars in the far-UV at <jats:italic>z</jats:italic> <jats:sub>em</jats:sub> &gt; 3.5, HE2QS J2311−1417 (<jats:italic>z</jats:italic> <jats:sub>em</jats:sub> = 3.70) and HE2QS J1630+0435 (<jats:italic>z</jats:italic> <jats:sub>em</jats:sub> = 3.81), obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. In the predominantly saturated He <jats:sc>ii</jats:sc> absorption spectra, both sight lines show several isolated resolved (FWHM ≳ 50 km s<jats:sup>−1</jats:sup>) transmission spikes in He <jats:sc>ii</jats:sc> Ly<jats:italic>α</jats:italic> and He <jats:sc>ii</jats:sc> Ly<jats:italic>β</jats:italic>. The incidence of such spikes decreases with increasing redshift, but both sight lines show significant spikes at <jats:italic>z</jats:italic> ≳ 3.5, signaling the presence of fully ionized regions in the <jats:italic>z</jats:italic> ≳ 3.5 intergalactic medium (IGM). We employ an automated algorithm to compare the number of detected He <jats:sc>ii</jats:sc> transmission spikes to predictions from mock spectra created from the outputs of a cubic (146 cMpc)<jats:sup>3</jats:sup> optically thin <jats:monospace>Nyx</jats:monospace> hydrodynamical simulation, assuming a range of UV background photoionization rates Γ<jats:sub>He <jats:sc>II</jats:sc> </jats:sub>. From the incidence of Ly<jats:italic>α</jats:italic> and Ly<jats:italic>β</jats:italic> transmission spikes we infer similar photoionization rates of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Gamma }}}_{\mathrm{He}{\rm\small{II}}}=({2.0}_{-0.5}^{+0.6})\times {10}^{-15}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabee17ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at 3.51 &lt; <jats:italic>z</jats:italic> &lt; 3.66 and Γ<jats:sub>He <jats:sc>II</jats:sc> </jats:sub> = (0.9 ± 0.3) × 10<jats:sup>−15</jats:sup> s<jats:sup>−1</jats:sup> at 3.460 &lt; <jats:italic>z</jats:italic> &lt; 3.685, respectively. Because the transmission spikes indicate fully ionized regions at <jats:italic>z</jats:italic> ≳ 3.5 along both lines of sight, our observations provide further evidence that He <jats:sc>ii</jats:sc> reionization had substantially progressed at these redshifts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the kinematic and chemical profiles of red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE)-2 survey in the direction of the Jhelum stellar stream, a Milky Way substructure located in the inner halo of the Milky Way at a distance from the Sun of ≈13 kpc. From the six APOGEE-2 Jhelum pointings, we isolate stars with log(<jats:italic>g</jats:italic>) &lt; 3.5, leaving a sample of 289 red giant stars. From this sample of APOGEE-2 giants, we identified seven stars that are consistent with the astrometric signal from Gaia DR2 for this stream. Of these seven, one falls onto the red giant branch (RGB) along the same sequence as the Jhelum stars presented by Ji et al. This new Jhelum member has [Fe/H] = −2.2 and is at the tip of the RGB. By selecting high orbital eccentricity, metal-rich stars, we identify red giants in our APOGEE2 sample that are likely associated with the Gaia-Enceladus-Sausage (GES) merger. We compare the abundance profiles of the Jhelum stars and GES stars and find similar trends in <jats:italic>α</jats:italic>-elements, as expected for low-metallicity populations. However, we find that the orbits for GES and Jhelum stars are not generally consistent with a shared origin. The chemical abundances for the APOGEE-2 Jhelum star and other confirmed members of the stream are similar to stars in known stellar streams and thus are consistent with an accreted dwarf galaxy origin for the progenitor of the stream, although we cannot rule out a globular cluster origin.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The recent advent of the Event Horizon Telescope (EHT) has made direct imaging of supermassive black holes a reality. Simulated images of black holes produced via general relativistic ray tracing and radiative transfer provide a key counterpart to these observational efforts. Black hole images have a wide range of physically interesting image structures, ranging from extremely fine scales in their lensed “photon rings” to the very large scales in their relativistic jets. The multiscale nature of the black hole system is therefore suitable for a multiscale approach to generate simulated images that capture all key elements of the system. Here, we present a prescription for adaptive ray tracing, which enables efficient computation of extremely high-resolution images of black holes. Using the polarized ray-tracing code <jats:sc>ipole</jats:sc>, we image a combination of semianalytic and general relativistic magnetohydrodynamic (GRMHD) models, and we show that images can be reproduced with a mean squared error of less than 0.1% even after tracing 12× fewer rays. We then use adaptive ray tracing to explore the properties of the photon ring. We illustrate the behavior of individual subrings in GRMHD simulations, and we explore their signatures in interferometric visibilities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Characterizing the atmospheres of planets orbiting M dwarfs requires understanding the spectral energy distributions of M dwarfs over planetary lifetimes. Surveys like MUSCLES, HAZMAT, and FUMES have collected multiwavelength spectra across the spectral type’s range of <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> and activity, but the extreme ultraviolet (EUV, 100–912 Å) flux of most of these stars remains unobserved because of obscuration by the interstellar medium compounded with limited detector sensitivity. While targets with observable EUV flux exist, there is no currently operational facility observing between 150 and 912 Å. Inferring the spectra of exoplanet hosts in this regime is critical to studying the evolution of planetary atmospheres because the EUV heats the top of the thermosphere and drives atmospheric escape. This paper presents our implementation of the differential emission measure technique to reconstruct the EUV spectra of cool dwarfs. We characterize our method’s accuracy and precision by applying it to the Sun and AU Mic. We then apply it to three fainter M dwarfs: GJ 832, Barnard’s star, and TRAPPIST-1. We demonstrate that with the strongest far-ultraviolet (FUV, 912–1700 Å) emission lines, observed with the Hubble Space Telescope and/or Far Ultraviolet Spectroscopic Explorer, and a coarse X-ray spectrum from either the Chandra X-ray Observatory or XMM-Newton, we can reconstruct the Sun’s EUV spectrum to within a factor of 1.8, with our model’s formal uncertainties encompassing the data. We report the integrated EUV flux of our M dwarf sample with uncertainties of a factor of 2–7 depending on available data quality.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The exact mechanism for the production of fast <jats:italic>γ</jats:italic>-ray variability in blazars remains debated. Magnetic reconnection, in which plasmoids filled with relativistic particles and magnetic fields are formed, is a viable candidate to explain the broadband electromagnetic spectrum and variability of these objects. Using state-of-the-art magnetic reconnection simulations, we generate realistic <jats:italic>γ</jats:italic>-ray light curves that would be observed with the Fermi Large Area Telescope. A comparison with observed <jats:italic>γ</jats:italic>-ray flares from flat spectrum radio quasars (FSRQs) reveals that magnetic reconnection events lead to comparable flux levels and variability patterns, in particular, when the reconnection layer is slightly misaligned with the line of sight. Emission from fast plasmoids moving close to the line of sight could explain the fast variability on the timescales of minutes for which evidence has been found in observations of FSRQs. Our results motivate improvements in existing radiative transfer simulations as well as dedicated searches for fast variability as evidence for magnetic reconnection events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the detection of [O <jats:sc>i</jats:sc>] 145.5 <jats:italic>μ</jats:italic>m in the BR 1202-0725 system, a compact group at <jats:italic>z</jats:italic> = 4.7 consisting of a quasar (QSO), a submillimeter-bright galaxy (SMG), and three faint Ly<jats:italic>α</jats:italic> emitters. By taking into account the previous detections and upper limits, the [O <jats:sc>i</jats:sc>] /[C <jats:sc>ii</jats:sc>] line ratios of the now five known high-<jats:italic>z</jats:italic> galaxies are higher than or on the high end of the observed values in local galaxies ([O <jats:sc>i</jats:sc>] /[C <jats:sc>ii</jats:sc>] ≳ 0.13). The high [O <jats:sc>i</jats:sc>] /[C <jats:sc>ii</jats:sc>] ratios and the joint analysis with previous detection of [N <jats:sc>ii</jats:sc>] lines for both of the QSO and the SMG suggest the presence of warm and dense neutral gas in these highly star-forming galaxies. This is further supported by new CO (12–11) line detections and a comparison with cosmological simulations. There is a possible positive correlation between the [N <jats:sc>ii</jats:sc>] 122/205 line ratio and the [O <jats:sc>i</jats:sc>] /[C <jats:sc>ii</jats:sc>] ratio when all local and high-<jats:italic>z</jats:italic> sources are taken into account, indicating that the denser the ionized gas, the denser and warmer the neutral gas (or vice versa). The detection of the [O <jats:sc>i</jats:sc>] line in the BR 1202-0725 system with a relatively short amount of integration with Atacama Large Millimeter/submillimeter Array (ALMA) demonstrates the great potential of this line as a dense gas tracer for high-<jats:italic>z</jats:italic> galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a compendium of disk galaxy scaling relations and a detailed characterization of their intrinsic scatter. Observed scaling relations are typically characterized by their slope, intercept, and scatter; however, these parameters are a mixture of observational errors and astrophysical processes. We introduce a novel Bayesian framework for computing the intrinsic scatter of scaling relations that accounts for nonlinear error propagation and covariant uncertainties. Bayesian intrinsic scatters are ∼25% more accurate than those obtained with a first-order classical method, which systematically underestimates the true intrinsic scatter. Structural galaxy scaling relations based on velocity (<jats:italic>V</jats:italic> <jats:sub>23.5</jats:sub>), size (<jats:italic>R</jats:italic> <jats:sub>23.5</jats:sub>), luminosity (<jats:italic>L</jats:italic> <jats:sub>23.5</jats:sub>), color (<jats:italic>g</jats:italic> − <jats:italic>z</jats:italic>), central stellar surface density (Σ<jats:sub>1</jats:sub>), stellar mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>), dynamical mass (<jats:italic>M</jats:italic> <jats:sub>dyn</jats:sub>), stellar angular momentum (<jats:italic>j</jats:italic> <jats:sub>*</jats:sub>), and dynamical angular momentum (<jats:italic>j</jats:italic> <jats:sub>dyn</jats:sub>) are examined to demonstrate the power and importance of the Bayesian formalism. Our analysis is based on a diverse selection of over 1000 late-type galaxies from the Photometry and Rotation Curve Observations from Extragalactic Surveys compilation with deep optical photometry and extended rotation curves. We determine the tightest relation for each parameter by intrinsic orthogonal scatter, finding <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> − <jats:italic>V</jats:italic> <jats:sub>23.5</jats:sub>, <jats:italic>R</jats:italic> <jats:sub>23.5</jats:sub> − <jats:italic>j</jats:italic> <jats:sub>*</jats:sub>, and <jats:italic>L</jats:italic> <jats:sub>23.5</jats:sub> − <jats:italic>j</jats:italic> <jats:sub>dyn</jats:sub> to be especially tight. The scatter of the <jats:italic>R</jats:italic> <jats:sub>23.5</jats:sub> − <jats:italic>L</jats:italic> <jats:sub>23.5</jats:sub>, <jats:italic>V</jats:italic> <jats:sub>23.5</jats:sub> − (<jats:italic>g</jats:italic> − <jats:italic>z</jats:italic>), and <jats:italic>R</jats:italic> <jats:sub>23.5</jats:sub> − <jats:italic>j</jats:italic> <jats:sub>dyn</jats:sub> relations is mostly intrinsic, making them ideal for galaxy formation and evolutionary studies. Our code to compute the Bayesian intrinsic scatter of any scaling relation is also presented. We quantify the correlated nature of many uncertainties in galaxy scaling relations and scrutinize the uncertain nature of disk inclination corrections and their effect on scatter estimates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the LIGO/Virgo GWTC-2 catalog to study the primary mass distribution of the merging black holes. We perform hierarchical Bayesian analysis and examine whether the mass distribution has a sharp cutoff for primary black hole masses below 65 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, as predicted in the pulsational pair-instability supernova model. We construct two empirical mass functions. One is a piece-wise function with two power-law segments joined by a sudden drop. The other consists of a main-truncated power-law component, a Gaussian component, and a third very massive component. Both models can reasonably fit the data and a sharp drop of the mass distribution is found at ∼50<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, suggesting that the majority of the observed black holes can be explained by the stellar evolution scenarios in which the pulsational pair-instability process takes place. On the other hand, the very massive subpopulation, which accounts for at most several percent of the total, may be formed through hierarchical mergers or other processes.</jats:p>