Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Fast Radio Bursts (FRBs) are extragalactic radio transients that exhibit a distance-dependent dispersion of their signal, and thus can be used as cosmological probes. In this article we, for the first time, apply a model-independent approach to measure reionization from synthetic FRB data assuming these signals are detected beyond redshift 5. This method allows us to constrain the full shape of the reionization history as well as the CMB optical depth <jats:italic>τ</jats:italic> while avoiding the problems of commonly used model-based techniques. A total of 100 localized FRBs, originating from redshifts 5–15, could constrain (at 68% confidence level) the CMB optical depth to within 11%, and the midpoint of reionization to 4%, surpassing current state-of-the-art CMB bounds and quasar limits. Owing to the higher numbers of expected FRBs at lower redshifts, the <jats:italic>τ</jats:italic> constraints are asymmetric (+14%, −7%), providing a much stronger lower limit. Finally, we show that the independent constraints on reionization from FRBs will improve limits on other cosmological parameters, such as the amplitude of the power spectrum of primordial fluctuations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We presented observations of PSRs J0614+2229 and J1938+2213 using the Five-hundred-meter Aperture Spherical radio Telescope. PSR J0614+2229 shows two distinct emission states, in which the emission of state A occurs earlier than that of state B in longitude. The phase offset between the average pulse profile peaks of the two states is about 1.°05. The polarization properties of the average pulse profile of the two states are different with different linear position angle swings. We found that the emission becomes brighter during the transition between the two states, which has never been seen in other mode-changing pulsars before. PSR J1938+2213 appears to consist of a weak emission state superposed by brighter burst emissions. The weak state is always present and the energy of the strongest pulse in the burst state is about 57 times larger than that of the average pulse energy. The polarization properties of the two states are also different, and orthogonal polarization modes can be seen only in the burst state, rather than both states. Our results suggest that, for the two pulsars, the emissions of the two states may be generated in different regions in the pulsar magnetosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Known sources of lithium (Li) in the universe include the Big Bang, novae, asymptotic giant branch stars, and cosmic-ray spallation. During their longer-lived evolutionary phases, stars are not expected to add to the Li budget of the Galaxy, but to largely deplete it. In this context, recent analyses of Li data from GALAH and LAMOST for field red clump (RC) stars have concluded that there is the need for a new production channel of Li, ubiquitous among low-mass stars, and that would be triggered on the upper red giant branch (RGB) or at helium ignition. This is distinct from the Li-rich giant problem and reflects bulk RC star properties. We provide an analysis of the GALAH Li data that accounts for the distribution of progenitor masses of field RC stars observed today. Such progenitors are different than today’s field RGB stars. Using standard post-main-sequence stellar evolution, we show that the distribution of Li among field RC giants as observed by GALAH is consistent with standard model predictions, and does not require new Li production mechanisms. Our model predicts a large fraction of very low Li abundances from low-mass progenitors, with higher abundances from higher mass ones. Moreover, there should be a large number of upper limits for RC giants, and higher abundances should correspond to higher masses. The most recent GALAH data indeed confirm the presence of large numbers of upper limits, and a much lower mean Li abundance in RC stars, in concordance with our interpretation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>One of the most pressing questions in cosmology is how the black holes (BHs) powering quasars at high redshift grow to supermassive scales within a billion years of the Big Bang. Here we show that sustained super-Eddington accretion can be achieved for BHs with Eddington fractions <jats:italic>f</jats:italic> <jats:sub>Edd</jats:sub> ≳ 2/<jats:italic>ϵ</jats:italic>, where <jats:italic>ϵ</jats:italic> is the efficiency with which radiation is generated in the accretion process. In this regime, the radiation carries too little momentum to halt the accretion flow and the infalling gas traps the radiation. The BH growth then proceeds unimpeded until the gas supply is exhausted, in contrast to accretion at lower rates, which is limited by the radiation generated in the accretion process. The large gas supply available in massive high-redshift quasar host galaxies may be readily accreted onto seed BHs via this supply-limited mode of accretion, providing an explanation for how such supermassive BHs are assembled in the early universe. This sustained super-Eddington growth may also explain the short lifetimes inferred for the H <jats:sc>ii</jats:sc> regions surrounding high-redshift quasars, if the bulk of the BH growth occurs without the associated radiation escaping to ionize the intergalactic medium. It furthermore implies that a population of obscured rapidly growing BHs may be difficult to detect, perhaps explaining why so few quasars with Eddington fractions higher than a few have been observed. Finally, this simple condition for sustained super-Eddington growth can easily be implemented in cosmological simulations that can be used to assess in which environments it occurs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The filamentary network of intergalactic medium (IGM) gas that gives origin to the Ly<jats:italic>α</jats:italic> forest in the spectra of distant quasars encodes information on the physics of structure formation and the early thermodynamics of diffuse baryonic material. Here we use a massive suite of more than 400 high-resolution cosmological hydrodynamical simulations run with the Graphics Processing Unit–accelerated code Cholla to study the IGM at high spatial resolution maintained over the entire computational volume. The simulations capture a wide range of possible IGM thermal histories by varying the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei. A statistical comparison of synthetic spectra with the observed 1D flux power spectra of hydrogen at redshifts 2.2 ≤ <jats:italic>z</jats:italic> ≤ 5.0 and with the helium Ly<jats:italic>α</jats:italic> opacity at redshifts 2.4 &lt; <jats:italic>z</jats:italic> &lt; 2.9 tightly constrains the photoionization and photoheating history of the IGM. By leveraging the constraining power of the available Ly<jats:italic>α</jats:italic> forest data to break model degeneracies, we find that the IGM experienced two main reheating events over 1.2 Gyr of cosmic time. For our best-fit model, hydrogen reionization completes by <jats:italic>z</jats:italic> <jats:sub> <jats:italic>R</jats:italic> </jats:sub> ≈ 6.0 with a first IGM temperature peak of <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> ≃ 1.3 × 10<jats:sup>4</jats:sup> K and is followed by the reionization of He <jats:sc>ii</jats:sc> that completes by <jats:italic>z</jats:italic> <jats:sub>R</jats:sub> ≈ 3.0 and yields a second temperature peak of <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> ≃ 1.4 × 10<jats:sup>4</jats:sup> K. We discuss how our results can be used to obtain information on the timing and the sources of hydrogen and helium reionization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an updated catalog of <jats:monospace>StrayCats</jats:monospace> (a catalog of NuSTAR stray light observations of X-ray sources) that includes nearly 18 additional months of observations. <jats:monospace>StrayCats</jats:monospace> v2 has an added 53 sequence IDs, 106 rows, and three new identified stray light (SL) sources in comparison to the original catalog. The total catalog now has 489 unique sequence IDs, 862 entries, and 83 confirmed <jats:monospace>StrayCats</jats:monospace> sources. Additionally, we provide new resources for the community to gauge the utility and spectral state of the source in a given observation. We have created long-term light curves for each identified SL source using MAXI and Swift/BAT data when available. Further, source extraction regions for 632 identified SL observations were created and are available to the public. In this paper we present an overview of the updated catalog and new resources for each identified <jats:monospace>StrayCats</jats:monospace> SL source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This is the fourth paper exploring the infrared properties of giant H <jats:sc>ii</jats:sc> regions with the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way giant H <jats:sc>ii</jats:sc> regions identified by Conti &amp; Crowther, and in this paper we present the 20 and 37 <jats:italic>μ</jats:italic>m imaging data we obtained from SOFIA for sources Sgr D and W42. Based upon the SOFIA data and other multiwavelength data, we derive and discuss the detailed physical properties of the individual compact sources and subregions as well as the large-scale properties of Sgr D and W42. However, improved measurements have revealed much closer distances to both regions than previously believed, and consequently, both sources are not powerful enough to be considered giant H <jats:sc>ii</jats:sc> regions any longer. Motivated by this, we revisit the census of giant H <jats:sc>ii</jats:sc> regions, performing a search of the last two decades of literature to update each source with the most recent and/or most accurate distance measurements. Based on these new distance estimates, we determine that 14 sources in total (25%) are at sufficiently reliable and closer distances that they are not powerful enough to be considered giant H <jats:sc>ii</jats:sc> regions. We briefly discuss the observational and physical characteristics specific to Sgr D and W42 and show that they have properties distinct from the giant H <jats:sc>ii</jats:sc> regions previously studied as a part of this survey.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We propose a triple-star scenario where the merger of two pre-main-sequence low-mass stars, ≲0.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, ejects a dusty equatorial outflow that obscures and temporarily causes the disappearance of a massive star, ≳8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The merger of the low-mass inner binary powers a faint outburst, i.e., a faint intermediate luminosity optical transient (ILOT), but its main effect that can last for decades is to (almost) disappear the luminous massive star of the triple system. The typical orbital period of the triple system is about 1 yr. The merger process proceeds as the more-massive star of the two low-mass pre-main-sequence stars starts to transfer mass to the least-massive star in the triple system and as a result of that expands. This type II obscuring ILOT scenario in a triple-star system might account for the fading, rebrightening, and then refading of the massive post-main-sequence star M101-OC1. It might recover in about 20–100 yr. Our study strengthens the claim that there are alternative scenarios to account for the (almost) disappearing of massive stars, removing the need for failed supernovae. In these scenarios the disappearing is temporary, lasting from months to decades, and therefore at a later time the massive star explodes as a core collapse supernova, even if it forms a black hole.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Although it is generally accepted that massive galaxies form in a two-phased fashion, beginning with a rapid mass buildup through intense starburst activities followed by primarily dry mergers that mainly deposit stellar mass at outskirts, the late time stellar mass growth of brightest cluster galaxies (BCGs), the most massive galaxies in the universe, is still not well understood. Several independent measurements have indicated a slower mass growth rate than predictions from theoretical models. We attempt to resolve the discrepancy by measuring the frequency of BCGs with multiple cores, which serve as a proxy of the merger rates in the central region and facilitate a more direct comparison with theoretical predictions. Using 79 BCGs at <jats:italic>z</jats:italic> = 0.06–0.15 with integral field spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, we obtain a multiple-core fraction of 0.11 ± 0.04 at <jats:italic>z</jats:italic> ≈ 0.1 within an 18 kpc radius from the center, which is comparable to the value of 0.08 ± 0.04 derived from mock observations of 218 simulated BCGs from the cosmological hydrodynamical simulation <jats:italic>IllustrisTNG</jats:italic>. We find that most cores that appear close to the BCGs from imaging data turn out to be physically associated systems. Anchoring on the similarity in the multiple-core frequency between the MaNGA and IllustrisTNG, we discuss the mass growth rate of BCGs over the past 4.5 Gyr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We solve for waves in an isothermal, stratified medium with a magnetic field that points along a direction perpendicular to that of gravity and varies exponentially in the direction of gravity. We find exact analytical solutions for two different cases: (a) waves propagating along the direction of the magnetic field and (b) waves propagating along the direction of the gravity. In each case, we find solutions in terms of either the hypergeometric functions or their confluent cousins. We solve the resultant transcendental dispersion relation numerically. The eigenfrequencies decrease with increasing degree of the spatial inhomogeneity of the magnetic field. Further, the nodes of the eigenfunctions leak toward regions of lower Alfvén wave speed due to softened wave-reflection in such regions. Such changes in the dispersion relation and the mode structures may allow the detection of magnetic fields buried in the stellar interior.</jats:p>