Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>In this paper, we collect a sample of stars observed both in LAMOST and Gaia, which have colors implying a temperature hotter than 7000 K. We train a machine-learning algorithm on LAMOST spectroscopic data which has been tagged with stellar classifications and metallicities, and use this machine to construct a catalog of blue horizontal branch stars (BHBs), together with metallicity information. Another machine is trained using Gaia parallaxes to predict absolute magnitudes for these stars. The final catalog of 13,693 BHBs is thought to be about 86% pure, with <jats:italic>σ</jats:italic> <jats:sub>[Fe/H]</jats:sub> ∼ 0.35 dex, and <jats:italic>σ</jats:italic> <jats:sub> <jats:italic>G</jats:italic> </jats:sub> ∼ 0.31 mag. These values are confirmed via comparison to globular clusters, although a covariance error seems to affect our magnitude and abundance estimates. We analyze a subset of this catalog in the Galactic Halo. We find that BHB populations in the outer halo appear redder, which could imply a younger population, and that the metallicity gradient is relatively flat around [Fe/H] = −1.9 dex over our sample footprint. We find that our metal-rich BHB stars are on more radial velocity dispersion-dominated orbits (<jats:italic>β</jats:italic> ∼ 0.70) at all radii than our metal-poor BHB stars (<jats:italic>β</jats:italic> ∼ 0.62).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Spatially resolved spectroscopy from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey has revealed a class of quiescent, relatively common early-type galaxies termed “red geysers” that possibly host large-scale active galactic nuclei–driven winds. Given their potential importance in maintaining a low level of star formation at late times, additional evidence confirming that winds are responsible for the red geyser phenomenon is critical. In this work, we present follow-up observations with the Echellette Spectrograph and Imager (ESI) at the Keck telescope of two red geysers (<jats:italic>z</jats:italic> &lt; 0.1) using multiple long slit positions to sample different regions of each galaxy. Our ESI data with a spectral resolution (<jats:italic>R</jats:italic>) ∼ 8000 improve upon MaNGA’s resolution by a factor of 4, allowing us to resolve the ionized gas velocity profiles along the putative wind cone with an instrumental resolution of <jats:italic>σ</jats:italic> = 16 km s<jats:sup>−1</jats:sup>. The line profiles of H<jats:italic>α</jats:italic> and [N <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic>6584 show asymmetric shapes that depend systematically on location: extended blue wings on the redshifted side of the galaxy and red wings on the opposite side. We construct a simple wind model and show that our results are consistent with geometric projections through an outflowing conical wind oriented at an angle toward the line of sight. An alternative hypothesis that assigns the asymmetric pattern to “beam smearing” of a rotating, ionized gas disk does a poor job matching the line asymmetry profiles. While our study features just two sources, it lends further support to the notion that red geysers are the result of galaxy-scale winds.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present new proper-motion measurements of optically emitting oxygen-rich knots of supernova remnant 1E 0102.2-7219 (E0102), which are used to estimate the remnant’s center of expansion and age. Four epochs of high-resolution Hubble Space Telescope images spanning 19 yr were retrieved and analyzed. We found a robust center of expansion of <jats:italic>α</jats:italic> = 1<jats:sup>h</jats:sup>04<jats:sup>m</jats:sup>02.ˢ48 and <jats:italic>δ</jats:italic> = −72°01′53.″92 (J2000) with 1<jats:italic>σ</jats:italic> uncertainty of 1.″77 using 45 knots from images obtained with the Advanced Camera for Surveys using the F475W filter in 2003 and 2013 having the highest signal-to-noise ratio. We also estimate an upper limit explosion age of 1738 ± 175 yr by selecting the knots with the highest proper motions and these knots are assumed to be the least decelerated. We find evidence of an asymmetry in the proper motions of the knots as a function of position angle. We conclude that these asymmetries were most likely caused by interaction between E0102's original supernova blast wave and an inhomogeneous surrounding environment, as opposed to intrinsic explosion asymmetry. The observed nonhomologous expansion suggests that the use of a free expansion model inaccurately offsets the center of expansion and leads to an overestimated explosion age. We discuss our findings as they compare to previous age and center of expansion estimates of E0102, as well as their relevance to a recently identified candidate central compact object.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>While dust is a major player in galaxy evolution, its relationship with gas and stellar radiation in the early universe is still not well understood. We combine 3D-Hubble Space Telescope emission-line fluxes with far-UV through far-IR photometry in a sample of 669 emission-line galaxies (ELGs) between 1.2 &lt; <jats:italic>z</jats:italic> &lt; 1.9 and use the <jats:monospace>MCSED</jats:monospace> spectral energy distribution fitting code to constrain the galaxies’ physical parameters, such as their star formation rates (SFRs), stellar masses, and dust masses. We find that the assumption of energy balance between dust attenuation and emission is likely unreasonable in many cases. We highlight a relationship between the mass-specific SFR, stellar mass, and dust mass, although its exact form is still unclear. Finally, a stacking of H<jats:italic>α</jats:italic> and H<jats:italic>β</jats:italic> fluxes shows that nebular attenuation increases with stellar mass and SFR for IR-bright ELGs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the results of ALMA observations toward the low-mass Class 0 binary system VLA 1623Aab in the Ophiuchus molecular cloud in <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, and C<jats:sup>18</jats:sup>O(2–1) lines. Our <jats:sup>12</jats:sup>CO (<jats:italic>J</jats:italic> = 2–1) data reveal that the VLA 1623 outflow consists of twin spatially overlapped outflows/jets. The redshifted northwestern jet exhibits three cycles of wiggle with a spatial period of 1360 ± 10 au, corresponding to a time period of 180 yr. The wiggle-like structure is also found in the position–velocity (PV) diagram, showing an amplitude in the velocity of about 0.9 km s<jats:sup>−1</jats:sup>. Both the period and velocity amplitude of the wiggle are roughly consistent with those expected from the binary parameters, i.e., the orbital period (460 ± 20 yr) and the Keplerian velocity (2.2 km s<jats:sup>−1</jats:sup>). Our <jats:sup>13</jats:sup>CO and C<jats:sup>18</jats:sup>O images show a dense gas nature in the two centimeter/millimeter sources, VLA 1623B and W, and its relation to the outflows, and strongly support the previous interpretation that both are shocked cloudlets. The driving sources of the twin molecular outflows are, therefore, likely to be the VLA 1623Aab binary. The outflow axes of the two molecular outflows are estimated to be inclined by 70° to each other across the plane of sky, implying that protostellar disks are also misaligned by <jats:inline-formula> <jats:tex-math> <?CDATA $70^\circ $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb810ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Such nature together with a small binary separation of 34 au in one of the youngest protobinary systems seems difficult to explain by disk fragmentation in quiescent environments. Other effects such as turbulence probably play roles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition region of quasi-perpendicular (<jats:italic>Q</jats:italic> <jats:sub>⊥</jats:sub>) shocks in the high-beta (<jats:italic>β</jats:italic> = <jats:italic>P</jats:italic> <jats:sub>gas</jats:sub>/<jats:italic>P</jats:italic> <jats:sub>B</jats:sub>) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfvén ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in the particle-in-cell (PIC) simulations of <jats:italic>Q</jats:italic> <jats:sub>⊥</jats:sub> shocks with sonic Mach numbers, <jats:italic>M</jats:italic> <jats:sub>s</jats:sub> = 2–3, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including <jats:italic>β</jats:italic> and the ion-to-electron mass ratio. In addition, the nonlinear evolution of the induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for <jats:italic>β</jats:italic> ≈ 20–100, the AIC instability could induce ion-scale waves and generate shock surface ripples in supercritical shocks above the AIC critical Mach number, <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{AIC}}^{* }\approx 2.3$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>AIC</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>≈</mml:mo> <mml:mn>2.3</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf1e1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Also, electron-scale waves are generated primarily by the whistler instability in these high-<jats:italic>β</jats:italic> shocks. The resulting multiscale waves from electron to ion scales are thought to be essential in the electron injection to diffusive shock acceleration in <jats:italic>Q</jats:italic> <jats:sub>⊥</jats:sub> shocks in the ICM.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Synchrotron radiation from hot gas near a black hole results in a polarized image. The image polarization is determined by effects including the orientation of the magnetic field in the emitting region, relativistic motion of the gas, strong gravitational lensing by the black hole, and parallel transport in the curved spacetime. We explore these effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the Walker–Penrose constant, we provide analytic estimates for the image polarization. We test this model using currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions, such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent with the clockwise rotation inferred from total intensity images.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a comprehensive analysis of the shape of dark matter (DM) halos in a sample of 25 Milky Way-like galaxies in TNG50 simulation. Using an enclosed volume iterative method, we infer an oblate-to-triaxial shape for the DM halo with median <jats:italic>T</jats:italic> ≃ 0.24. We group DM halos into three different categories. Simple halos (32% of the population) establish principal axes whose ordering in magnitude does not change with radius and whose orientations are almost fixed throughout the halo. Twisted halos (32%) experience levels of gradual rotations throughout their radial profiles. Finally, stretched halos (36%) demonstrate a stretching in the lengths of their principal axes where the ordering of different eigenvalues changes with radius. Subsequently, the halo experiences a “rotation” of ∼90° where the stretching occurs. Visualizing the 3D ellipsoid of each halo, for the first time, we report signs of a reorienting ellipsoid in twisted and stretched halos. We examine the impact of baryonic physics on DM halo shape through a comparison to dark matter only (DMO) simulations. This suggests a triaxial (prolate) halo. We analyze the impacts of substructure on DM halo shape in both hydrodynamical and DMO simulations and confirm that they are subdominant. We study the distribution of satellites in our sample. In simple and twisted halos, the angle between satellites’ angular momentum and the galaxy’s angular momentum grows with radius. However, stretched halos show a flat distribution of angles. Overlaying our theoretical outcome on the observational results presented in the literature establishes a fair agreement.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We continue to investigate two-dimensional laterally propagating flames in type I X-ray bursts using fully compressible hydrodynamics simulations. In the current study we relax previous approximations where we artificially boosted the flames. We now use more physically realistic reaction rates, thermal conductivities, and rotation rates, exploring the effects of neutron star rotation rate and thermal structure on the flame. We find that at lower rotation rates the flame becomes harder to ignite, whereas at higher rotation rates the nuclear burning is enhanced by increased confinement from the Coriolis force and the flame propagates steadily. At higher crustal temperatures, the flame moves more quickly and accelerates as it propagates through the atmosphere. If the temperature is too high, instead of a flame propagating across the surface the entire atmosphere burns uniformly. Our findings could have implications for the relationship between observed burst rise times and neutron star rotation and accretion rates. All of the software used for these simulations is freely available.</jats:p>