Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We study the propagation of mildly relativistic cosmic rays (CRs) in multiphase interstellar medium environments with conditions typical of nearby disk galaxies. We employ the techniques developed in Armillotta et al. to postprocess three high-resolution TIGRESS magnetohydrodynamic simulations modeling local patches of star-forming galactic disks. Together, the three simulations cover a wide range of gas surface density, gravitational potential, and star formation rate (SFR). Our prescription for CR propagation includes the effects of advection by the background gas, streaming along the magnetic field at the local ion Alfvén speed, and diffusion relative to the Alfvén waves, with the diffusion coefficient set by the balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We find that the combined transport processes are more effective in environments with higher SFR. These environments are characterized by higher-velocity hot outflows (created by clustered supernovae) that rapidly advect CRs away from the galactic plane. As a consequence, the ratio of midplane CR pressure to midplane gas pressures decreases with increasing SFR. We also use the postprocessed simulations to make predictions regarding the potential dynamical impacts of CRs. The relatively flat CR pressure profiles near the midplane argue that they would not provide significant support against gravity for most of the ISM mass. However, the CR pressure gradients are larger than the other pressure gradients in the extraplanar region (∣<jats:italic>z</jats:italic>∣ &gt; 0.5 kpc), suggesting that CRs may affect the dynamics of galactic fountains and/or winds. The degree of this impact is expected to increase in environments with lower SFR.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Fossil cluster A2261 is well studied, but previous studies give contradictory results on its dynamical states, such as its X-ray central entropy and magnitude gap. To improve our understanding of its dynamical state, we conduct multiobject spectroscopic observations with Hectospec on the MMT, covering an area out to 5 virial radii from the cluster center, and get improved completeness and membership. Using these new data, we calculate multiple dynamical indicators, including Gaussianity, distance offset, and velocity offset. These indicators suggest that A2261 is moderately relaxed. However, a Dressler–Shectman test reveals a group candidate to the south at a projected distance that is near the virial radius and overlaps with an X-ray tail-like feature. One of the galaxies associated with that group would be sufficiently bright to reduce the fossil magnitude gap. This raises the possibility that A2261 could have recently transited in fossil status, if the group had previously crossed the cluster and is only now found outside. In the cluster outskirts, we see an extended feature of galaxies located on the opposite side of the cluster from the group candidate. On even larger scales, we find that this feature connects, both on the sky and in velocity space, with a long (4.4 Mpc) filamentary structure in the Sloan Digital Sky Survey data. This could support the idea that a group was fed into the cluster through the filament, temporarily breaking the fossil status and resulting in a minor merger that weakly disturbed the intracluster medium of the cluster.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the variation in the single-pulse emission from PSR J1900+4221 (CRAFTS 19C10) observed at frequency centered at 1.25 GHz using the Five-hundred-meter Aperture Spherical radio Telescope. The integrated pulse profile shows two distinct components, referred to here as the leading and trailing components, with the latter component also containing a third weak component. The single-pulse sequence reveals different emissions demonstrating as nulling, regular, and bright pulses, each with a particular abundance and duration distribution. There also exists pulses that follow a log-normal distribution suggesting the possibility of another emission, in which the pulsar is radiating weakly. Changes in the profile shape are seen across different emissions. We examine the emission variations in the leading and trailing components collectively and separately, and find moderate correlation between the two components. The inclination angle is estimated to be about 7° based on pulse-width, and we discuss that nulling in this pulsar does not seem to show correlation with age and rotation period.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The observationally inferred crystalline abundance in silicates in comets, which should have been formed in the outer region of a protoplanetary disk, is relatively high (∼10%–60%), although crystalline silicates would be formed by the annealing of amorphous precursors in the inner disk region. In order to quantitatively address this puzzle, we performed a Monte Carlo simulation of the advection/diffusion of silicate particles in a turbulent disk in a setting based on the pebble accretion model: pebbles consisting of many small amorphous silicates embedded in an icy mantle are formed in the outer disk region, silicate particles are released at the snow line, crystalline silicate particles are produced at the annealing line, silicate particles diffuse beyond the snow line, and they eventually stick to drifting pebbles to return to the snow line. In the simple case without sticking and with steady pebble flux, we show through the simulations and analytical arguments that the crystalline components in silicate materials beyond the snow line are robustly and uniformly ≃5%. On the other hand, in a more realistic case with sticking and with a decaying pebble flux, the crystalline abundance increases to ∼20%–25%, depending on the ratio of the decay to diffusion timescales. This abundance is consistent with the observations. In this investigation, we assume a simple steady-accretion disk. The simulations coupled with the disk evolution are needed for a more detailed comparison with observed data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the Fermi-LAT observations of the behind-the-limb (BTL) flare of 2021 July 17 and the joint detection of this flare by STIX on board the Solar Orbiter. The separation between Earth and the Solar Orbiter was 99.°2 at 05:00 UT, allowing STIX to have a front view of the flare. The location of the flare was S20E140 in Stonyhurst heliographic coordinates, making this the most distant behind-the-limb flare ever detected in &gt;100 MeV gamma-rays. The LAT detection lasted for ∼16 minutes, the peak flux was 3.6 ± 0.8 (10<jats:sup>−5</jats:sup>) ph cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> with a significance &gt;15<jats:italic>σ</jats:italic>. A coronal wave was observed from both STEREO-A and SDO in extreme ultraviolet (EUV), with an onset on the visible disk in coincidence with the LAT onset. A complex type II radio burst was observed by GLOSS also in coincidence with the onset of the LAT emission, indicating the presence of a shock wave. We discuss the relation between the time derivative of the EUV wave intensity profile at 193 Å as observed by STEREO-A and the LAT flux to show that the appearance of the coronal wave at the visible disk and the acceleration of protons as traced by the observed &gt;100 MeV gamma-ray emission are coupled. We also report how this coupling is present in the data from three other BTL flares detected by Fermi-LAT, suggesting that the protons driving the gamma-ray emission of BTL solar flares and the coronal wave share a common origin.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a well-designed sample of more than 1000 type 1 quasars at 3.5 &lt; <jats:italic>z</jats:italic> &lt; 5 and derive UV quasar luminosity functions (QLFs) in this redshift range. These quasars were selected using the Sloan Digital Sky Survey (SDSS) imaging data in the Stripe 82 and overlap regions with repeat imaging observations that are about 1 mag fainter than the SDSS single-epoch data. The follow-up spectroscopic observations were conducted by the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) as one of the BOSS ancillary programs. Reaching <jats:italic>i</jats:italic> ∼ 21.5 mag, our sample bridges previous samples from brighter and deeper surveys. We use a 1/<jats:italic>V</jats:italic> <jats:sub>a</jats:sub> method to derive binned QLFs at 3.6 &lt; <jats:italic>z</jats:italic> &lt; 4.0, 4.0 &lt; <jats:italic>z</jats:italic> &lt; 4.5, and 4.5 &lt; <jats:italic>z</jats:italic> &lt; 4.9 and then use a double power-law model to parameterize the QLFs. We also combine our data with literature QLFs to better constrain the QLFs across a much wider luminosity baseline. The faint- and bright-end slopes of the QLFs in this redshift range are around −1.7 and −3.7, respectively, with uncertainties from 0.2 to 0.3 to &gt;0.5. The evolution of the QLFs from <jats:italic>z</jats:italic> ∼ 5 to 3.5 can be described by a pure density evolution model (∝10<jats:sup> <jats:italic>kz</jats:italic> </jats:sup>) with a parameter <jats:italic>k</jats:italic> similar to that at 5 &lt; <jats:italic>z</jats:italic> &lt; 7, suggesting a nearly uniform evolution of the quasar density at <jats:italic>z</jats:italic> = 3.5–7.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>FRB 180916.J0158+65 is one of the nearest, periodically repeating, and actively bursting fast radio bursts (FRBs) that has been localized to the outskirts of a spiral galaxy. In this work we study the FRB with the hard X-ray 14–195 keV data from the Burst Alert Telescope (BAT) on board The Neil Gehrels Swift Observatory. BAT uses coded mask technology giving a localization of ≲3′ in the hard X-ray band, along with an accurate background estimation. BAT has been observing the source location in survey mode since 2020 February. The survey mode observations involve background subtracted spectra, integrated over a time span ranging 300–2000 s at the source location (from 2022 February–2022 January). We analyzed all the ∼230 survey mode observations from BAT and checked for any signal in any of the observations. We did not detect any signal at &gt;5<jats:italic>σ</jats:italic> confidence level in any of the observations. We could estimate a 5<jats:italic>σ</jats:italic> upper limit on the 14–195 keV flux, which ranged between 4.5 × 10<jats:sup>−10</jats:sup>–7.6 × 10<jats:sup>−9 </jats:sup>erg cm<jats:sup>−2 </jats:sup>s<jats:sup>−1</jats:sup>. At the source distance this relates to a 5<jats:italic>σ</jats:italic> upper limit on a luminosity of 5.08 × 10<jats:sup>44</jats:sup>–8.5 × 10<jats:sup>45 </jats:sup>erg s<jats:sup>−1</jats:sup>. With this estimate, we could rule out any persistent X-ray emission at the source location for these snapshots of BAT observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Ca <jats:sc>ii</jats:sc> H and K lines are among the few features available to infer the metallicity of extremely metal-poor stars from medium-resolution spectroscopy. Unfortunately, these lines can overlap with absorption produced in the intervening interstellar medium, introducing systematic errors in the derived metallicities. The strength of the Ca <jats:sc>ii</jats:sc> infrared triplet lines can also be measured at extremely low metallicities, and it is not affected by interstellar absorption, but it suffers significant departures from local thermodynamic equilibrium (LTE). We investigate the feasibility of adopting the Ca <jats:sc>ii</jats:sc> infrared triplet as a metallicity indicator in extremely metal-poor stars using state-of-the art non-LTE models including the most recent atomic data. We find that the triplet lines exhibit non-LTE abundance corrections that can exceed 0.5 dex. When interstellar absorption affecting the Ca <jats:sc>ii</jats:sc> resonance lines is accounted for using high-resolution observations, the agreement between non-LTE abundances for the triplet and those for the resonance lines, with only minor departures from LTE, is excellent. Non-LTE effects strengthen the Ca <jats:sc>ii</jats:sc> IR triplet lines, facilitating measurements at very low metallicities, compared with LTE estimates, down to [Fe/H] = −6.0. This result has important implications for the discovery of primitive stars in our Galaxy and others, since instruments are most sensitive at red/near-infrared wavelengths, and tens of millions of spectra covering the Ca <jats:sc>ii</jats:sc> IR triplet will soon become available from the Gaia, DESI, WEAVE, and PFS missions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We derive the first detailed chemical abundances of three star clusters in the Large Magellanic Cloud (LMC), NGC 1831 (436 ± 22 Myr), NGC 1856 (350 ± 18 Myr), and [SL63]268 (1230 ± 62 Myr) using integrated-light spectroscopic observations obtained with the Magellan Echelle spectrograph on Magellan Baade telescope. We derive [Fe/H], [Mg/Fe], [Ti/Fe], [Ca/Fe], [Ni/Fe], [Mn/Fe], [Cr/Fe], and [Na/Fe] for the three clusters. Overall, our results match the LMC abundances obtained in the literature as well as those predicted by detailed chemical evolution models. For clusters NGC 1831 and NGC 1856, the [Mg/Fe] ratios appear to be slightly depleted compared with [Ca/Fe] and [Ti/Fe]. This could be hinting at the well-known Mg–Al abundance anti-correlation observed in several Milky Way globular clusters. We note, however, that higher signal-to-noise observations are needed to confirm such a scenario, particularly for NGC 1831. We also find a slightly enhanced integrated-light [Na/Fe] ratio for cluster [SL63]268 compared with those from the LMC field stars, possibly supporting a scenario of intracluster abundance variations. We stress that detailed abundance analysis of individual stars in these LMC clusters is required to confirm the presence or absence of multiple stellar populations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the evolution of the flux power spectrum in the Cosmic Reionization On Computers simulations. We find that, contrary to some previous studies, the shape of the flux power spectrum is rather insensitive to the timing of reionization. However, the amplitude of the flux power spectrum does strongly evolve with time, and that evolution is almost perfectly correlated with the timing of reionization. We show how such correlation can be used in a (futuristic) measurement to determine the redshift of overlap of ionized bubbles.</jats:p>