Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>In this paper we examine the factors that shape the distribution of molecular gas surface densities on the 150 pc scale across 67 morphologically diverse star-forming galaxies in the PHANGS-ALMA CO (2–1) survey. Dividing each galaxy into radial bins, we measure molecular gas surface density contrasts, defined here as the ratio between a fixed high percentile of the CO distribution and a fixed reference level in each bin. This reference level captures the level of the faint CO floor that extends between bright filamentary features, while the intensity level of the higher percentile probes the structures visually associated with bright, dense interstellar medium features like spiral arms, bars, and filaments. We compare these contrasts to matched percentile-based measurements of the 3.6 <jats:italic>μ</jats:italic>m emission measured using Spitzer/IRAC imaging, which trace the underlying stellar mass density. We find that the logarithms of CO contrasts on 150 pc scales are 3–4 times larger than, and positively correlated with, the logarithms of 3.6 <jats:italic>μ</jats:italic>m contrasts probing smooth nonaxisymmetric stellar bar and spiral structures. The correlation appears steeper than linear, consistent with the compression of gas as it flows supersonically in response to large-scale stellar structures, even in the presence of weak or flocculent spiral arms. Stellar dynamical features appear to play an important role in setting the cloud-scale gas density in our galaxies, with gas self-gravity perhaps playing a weaker role in setting the 150 pc scale distribution of gas densities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Atmospheric retrievals of exoplanetary transmission spectra provide important constraints on various properties, such as chemical abundances, cloud/haze properties, and characteristic temperatures, at the day–night atmospheric terminator. To date, most spectra have been observed for giant exoplanets due to which retrievals typically assume hydrogen-rich atmospheres. However, recent observations of mini Neptunes/super-Earths, and the promise of upcoming facilities including the James Webb Space Telescope (JWST), call for a new generation of retrievals that can address a wide range of atmospheric compositions and related complexities. Here we report Aurora, a next-generation atmospheric retrieval framework that builds upon state-of-the-art architectures and incorporates the following key advancements: (a) a generalized compositional retrieval allowing for H-rich and H-poor atmospheres, (b) a generalized prescription for inhomogeneous clouds/hazes, (c) multiple Bayesian inference algorithms for high-dimensional retrievals, (d) modular considerations for refraction, forward scattering, and Mie scattering, and (e) noise modeling functionalities. We demonstrate Aurora on current and/or synthetic observations of the hot Jupiter HD 209458 b, mini Neptune K2-18b, and rocky exoplanet TRAPPIST-1 d. Using current HD 209458 b spectra, we demonstrate the robustness of our framework and cloud/haze prescription against assumptions of H-rich/H-poor atmospheres, improving on previous treatments. Using real and synthetic spectra of K2-18b, we demonstrate an agnostic approach to confidently constrain its bulk atmospheric composition and obtain precise abundance estimates. For TRAPPIST-1 d, 10 JWST-NIRSpec transits can enable identification of the main atmospheric component for cloud-free, CO<jats:sub>2</jats:sub>-rich, and N<jats:sub>2</jats:sub>-rich atmospheres and abundance constraints on trace gases, including initial indications of O<jats:sub>3</jats:sub> if present at enhanced levels (∼10×–100× Earth levels).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of nonthermal radiation. The inner 375 pc × 600 pc region, called the Central Molecular Zone, is home to the supermassive black hole Sagittarius A*, massive cloud complexes, and particle accelerators such as supernova remnants (SNRs). We present the results of our improved analysis of the very-high-energy gamma-ray emission above 2 TeV from the GC using 125 hr of data taken with the Very Energetic Radiation Imaging Telescope Array System imaging-atmospheric Cerenkov telescope between 2010 and 2018. The central source VER J1745–290, consistent with the position of Sagittarius A*, is detected at a significance of 38 standard deviations above the background level (38<jats:italic>σ</jats:italic>), and we report its spectrum and light curve. Its differential spectrum is consistent with a power law with exponential cutoff, with a spectral index of <jats:inline-formula> <jats:tex-math> <?CDATA ${2.12}_{-0.17}^{+0.22}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf926ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, a flux normalization at 5.3 TeV of <jats:inline-formula> <jats:tex-math> <?CDATA ${1.27}_{-0.23}^{+0.22}\times {10}^{-13}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf926ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> TeV<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, and cutoff energy of <jats:inline-formula> <jats:tex-math> <?CDATA ${10.0}_{-2.0}^{+4.0}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf926ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> TeV. We also present results on the diffuse emission near the GC, obtained by combining data from multiple regions along the GC ridge, which yield a cumulative significance of 9.5<jats:italic>σ</jats:italic>. The diffuse GC ridge spectrum is best fit by a power law with a hard index of 2.19 ± 0.20, showing no evidence of a cutoff up to 40 TeV. This strengthens the evidence for a potential accelerator of PeV cosmic rays being present in the GC. We also provide spectra of the other sources in our field of view with significant detections, composite SNR G0.9+0.1, and HESS J1746–285.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent studies have detected structurally bound water in the refractory silicate minerals present in ordinary and enstatite chondrite meteorites. The mechanism for the incorporation of the hydrogen is not well defined. In this paper we quantitatively examine a two-fold process involving the implantation and diffusion of nebular hydrogen ions that is responsible for the hydration of the chondritic minerals. Our simulations show that depending on critical parameters, including the flux of the protons in nebular plasma, retention coefficient, temperature of the silicate minerals, and desorption rate of implanted hydrogen, the implantation of low-energy hydrogen ions can result in equivalent water contents of ∼0.1 wt% in chondritic silicates within 10 years. Thus, this novel mechanism operating in the nebula at 10<jats:sup>−3</jats:sup> bar pressure and &lt;650 K temperatures can efficiently hydrate the free-floating chondritic minerals prior to the rapid formation of planetesimals inside the snow line, and agree well with the wet accretion scenario for the inner solar system objects.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The polarimetric observations of the protoplanetary disk around HL Tau have shown the scattering-induced polarization at ALMA Band 7, which indicates that the maximum dust size is ∼100 <jats:italic>μ</jats:italic>m, while the spectral energy distribution (SED) has suggested that the maximum dust size is approximately a millimeter. To solve the contradiction, we investigate the impact of differential settling of dust grains on the SED and polarization. If the disk is optically thick, a longer observing wavelength traces more interior layers, which would be dominated by larger grains. We find that the SED of the center part of the HL Tau disk can be explained with millimeter-sized grains for a broad range of turbulence strength, while 160 <jats:italic>μ</jats:italic>m–sized grains cannot be explained unless the turbulence strength parameter <jats:italic>α</jats:italic> <jats:sub>t</jats:sub> is lower than 10<jats:sup>−5</jats:sup>. We also find that the observed polarization fraction can be potentially explained with a maximum dust size of 1 mm if <jats:italic>α</jats:italic> <jats:sub>t</jats:sub> ≲ 10<jats:sup>−5</jats:sup>, although models with 160 <jats:italic>μ</jats:italic>m–sized grains are also acceptable. However, if the maximum dust size is ∼3 mm, the simulated polarization fraction is too low to explain the observations even if the turbulence strength is extremely small, indicating a maximum dust size of ≲1 mm. The degeneracy between 100 <jats:italic>μ</jats:italic>m– and millimeter-sized grains can be solved by improving the ALMA calibration accuracy or polarimetric observations at (sub)centimeter wavelengths.</jats:p>