Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Full-physics cosmological simulations are powerful tools for studying the formation and evolution of structure in the universe but require extreme computational resources. Here, we train a convolutional neural network to use a cheaper <jats:italic>N</jats:italic>-body-only simulation to reconstruct the baryon hydrodynamic variables (density, temperature, and velocity) on scales relevant to the Ly<jats:italic>α</jats:italic> forest, using data from <jats:monospace>Nyx</jats:monospace> simulations. We show that our method enables rapid estimation of these fields at a resolution of ∼20 kpc, and captures the statistics of the Ly<jats:italic>α</jats:italic> forest with much greater accuracy than existing approximations. Because our model is fully convolutional, we can train on smaller simulation boxes and deploy on much larger ones, enabling substantial computational savings. Furthermore, as our method produces an approximation for the hydrodynamic fields instead of Ly<jats:italic>α</jats:italic> flux directly, it is not limited to a particular choice of ionizing background or mean transmitted flux.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar filament eruptions can generate coronal mass ejections (CMEs), which are huge threats to space weather. Thus, we need to understand their underlying mechanisms. Although many authors have studied the mechanisms for several decades, we still do not fully understand in what conditions a filament can erupt to become a CME or not. Previous studies have discussed extensively why a highly twisted and already erupted filament will be interrupted and considered that a strong overlying constraint field seems to be the key factor. However, few of them study filaments in the weak field, namely, quiescent filaments, as it is too hard to reconstruct the magnetic configuration there. Here we show a case study, in which we can fully reconstruct the configuration of an intermediate filament with the MHD-relaxation extrapolation model and discuss its initial eruption and eventual failure. By analyzing the magnetic configuration, we suggest that the reconnection between the erupting magnetic flux rope (MFR) and the overlying field are the key factors that constrained the eruption of the filament. There is observational evidence that MFRs will reconnect with peripheral field lines. Usually, the reconnection between an MFR and peripheral fields will weaken the overlying constraint and promote further eruption, but in some cases in which the magnetic configuration of an MFR is far different from peripheral fields, the reconnection will play a negative role in MFR eruption.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A1689-zD1 is one of the most distant galaxies, discovered with the aid of gravitational lensing, providing us with an important opportunity to study galaxy formation in the very early universe. In this study, we report the detection of [C <jats:sc>ii</jats:sc>]158 <jats:italic>μ</jats:italic>m and [O <jats:sc>iii</jats:sc>]88 <jats:italic>μ</jats:italic>m emission lines of A1689-zD1 in the Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 8. We measure the redshift of this galaxy as <jats:italic>z</jats:italic> <jats:sub>sys</jats:sub> = 7.133 ± 0.005 based on the [C <jats:sc>ii</jats:sc>] and [O <jats:sc>iii</jats:sc>] emission lines, consistent with that adopted by Bakx et al. The observed <jats:italic>L</jats:italic> <jats:sub>[O <jats:sc>III</jats:sc>]</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>II</jats:sc>]</jats:sub> ratio is 2.09 ± 0.09, higher than that of most of the local galaxies, but consistent with other <jats:italic>z</jats:italic> ∼ 7 galaxies. The moderate spatial resolution of ALMA data provided us with a precious opportunity to investigate spatial variation of <jats:italic>L</jats:italic> <jats:sub>[O <jats:sc>III</jats:sc>]</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>II</jats:sc>]</jats:sub>. In contrast to the average value of 2.09, we find a much higher <jats:italic>L</jats:italic> <jats:sub>[O <jats:sc>III</jats:sc>]</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>II</jats:sc>]</jats:sub> of ∼7 at the center of the galaxy. This spatial variation of <jats:italic>L</jats:italic> <jats:sub>[O <jats:sc>III</jats:sc>]</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>[C <jats:sc>II</jats:sc>]</jats:sub> was seldom reported for other high-<jats:italic>z</jats:italic> galaxies. It is also interesting that the peak of the ratio does not overlap with optical peaks. Possible physical reasons include a central active galactic nucleus, shock heating from merging, and a starburst. Our moderate spatial resolution data also reveal that in addition to the observed two clumps shown in previous Hubble Space Telescope images, there is a redshifted segment to the west of the northern optical clump. This structure is consistent with previous claims that A1689-zD1 is a merging galaxy, but with the northern redshifted part being some ejected material, or that the northern redshifted material stems from a third more highly obscured region of the galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the latest results of a Parkes multibeam survey for pulsars and dispersed radio bursts in the Large Magellanic Cloud (LMC). We conducted both periodicity and single-pulse searches at a much larger range of trial dispersion measures (DMs) than previously searched. We detected 229 single pulses with signal-to-noise ratio (S/N) &gt; 7 that were classified by the deep-learning network FETCH as being real (with &gt;90% likelihood), of which nine were from the known giant-pulse-emitting pulsar PSR B0540−69. Two possibly repeating sources were detected with DMs suggesting that they lie within the LMC, but these require confirmation. Only three of the 220 unknown pulses had S/N &gt; 8, and the DM distribution for these detected pulses follows an exponential falloff with increasing DM and does not show any excess of signals at DM values expected for the LMC. These features suggest that the detected pulses are not likely to be real, although they are visually compelling. We also report the discovery of a new pulsar (PSR J0556−67) in our periodicity search. This pulsar has a spin period of 791 ms, a DM of 71 cm<jats:sup>−3</jats:sup> pc, an estimated 1400 MHz flux density of ∼0.12 mJy, and shows no evidence of binary motion. Future observations may be able to confirm whether any of the weak but promising candidates in our single-pulse and periodicity searches, including our two possible repeaters, are real or not.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Inspired by observations of sunspots embedded in active regions, it is often assumed that large-scale, strong magnetic flux emerges from the Sun’s deep interior in the form of arched, cylindrical structures, colloquially known as flux tubes. Here, we continue to examine the different dynamics encountered when these structures are considered as concentrations in a volume-filling magnetic field rather than as isolated entities in a field-free background. Via 2.5D numerical simulations, we consider the buoyant rise of magnetic flux concentrations from a radiative zone through an overshooting convection zone that self-consistently (via magnetic pumping) arranges a volume-filling large-scale background field. This work extends earlier papers that considered the evolution of such structures in a purely adiabatic stratification with an assumed form of the background field. This earlier work established the existence of a bias that created an increased likelihood of the successful rise for magnetic structures with one (relative) orientation of twist and a decreased likelihood for the other. When applied to the solar context, this bias is commensurate with the solar hemispherical helicity rules (SHHRs). This paper establishes the robustness of this selection mechanism in a model incorporating a more realistic background state, consisting of overshooting convection and a turbulently pumped mean magnetic field. Ultimately, convection only weakly influences the selection mechanism, since it is enacted at the initiation of the rise, at the edge of the overshoot zone. Convection does however add another layer of statistical fluctuations to the bias, which we investigate in order to explain variations in the SHHRs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore a new approach for extracting reionization-era contributions to the kinetic Sunyaev–Zel’dovich (kSZ) effect. Our method utilizes the cross-power spectrum between filtered and squared maps of the cosmic microwave background (CMB) and photometric galaxy surveys during the Epoch of Reionization (EoR). This kSZ<jats:sup>2</jats:sup>–galaxy cross-power spectrum statistic has been successfully detected at lower redshifts (<jats:italic>z</jats:italic> ≲ 1.5). Here we extend this method to <jats:italic>z</jats:italic> ≳ 6 as a potential means to extract signatures of patchy reionization. We model the expected signal across multiple photometric redshift bins using seminumeric simulations of the reionization process. In principle, the cross-correlation statistic robustly extracts reionization-era contributions to the kSZ signal, while its redshift evolution yields valuable information regarding the timing of reionization. Specifically, the model cross-correlation signal near <jats:italic>ℓ</jats:italic> ∼ 1000 peaks during the early stages of the EoR, when about 20% of the volume of the universe is ionized. Detectable <jats:italic>ℓ</jats:italic> modes mainly reflect squeezed-triangle configurations of the related bispectrum, quantifying correlations between the galaxy overdensity field on large scales and the smaller-scale kSZ power. We forecast the prospects for detecting this signal using future wide-field samples of Lyman-break galaxies from the Roman Space Telescope and next-generation CMB surveys including the Simons Observatory, CMB-S4, and CMB-HD. We find that a roughly 13<jats:italic>σ</jats:italic> detection is possible for CMB-HD and Roman after summing over all <jats:italic>ℓ</jats:italic> modes. We discuss the possibilities for improving this approach and related statistics, with the aim of moving beyond simple detections to measure the scale and redshift dependence of the cross-correlation signals.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Zwicky Transient Facility follow-up campaign of alerts released by the IceCube Neutrino Observatory has led to the likely identification of the transient AT2019fdr as the source of the neutrino event IC200530A. AT2019fdr was initially suggested to be a tidal disruption event in a Narrow-Line Seyfert 1 galaxy. However, the combination of its spectral properties, color evolution, and feature-rich light curve suggests that AT2019fdr may be a Type IIn superluminous supernova. In the latter scenario, IC200530A may have been produced via inelastic proton-proton collisions between the relativistic protons accelerated at the forward shock and the cold protons of the circumstellar medium. Here, we investigate this possibility and find that at most 4.6 × 10<jats:sup>−2</jats:sup> muon neutrino and antineutrino events are expected to be detected by the IceCube Neutrino Observatory within 394 days of discovery in the case of excellent discrimination of the atmospheric background. After correcting for the Eddington bias, which occurs when a single cosmic neutrino event is adopted to infer the neutrino emission at the source, we conclude that IC200530A may originate from the hydrogen-rich superluminous supernova AT2019fdr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>After the successful detection of a gravitational-wave (GW) signal and its associated electromagnetic (EM) counterparts from GW170817, neutron star–black hole (NSBH) mergers have been highly expected to be the next type of multimessenger source. However, despite the detection of several NSBH merger candidates during the GW third observation run, no confirmed EM counterparts from these sources have been identified. The most plausible explanation is that these NSBH merger candidates were plunging events mainly because the primary black holes (BHs) had near-zero projected aligned spins based on GW observations. In view of the fact that neutron stars (NSs) can be easily tidally disrupted by BHs with high projected aligned spins, we study an evolution channel to form NSBH binaries with fast-spinning BHs, the properties of BH mass and spin, and their associated tidal disruption probability. We find that if the NSs are born first, the companion helium stars would be tidally spun up efficiently, and would thus finally form fast-spinning BHs. If BHs do not receive significant natal kicks at birth, these NSBH binaries that can merge within Hubble time would have BHs with projected aligned spins <jats:italic>χ</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub> ≳ 0.8 and, hence, can certainly allow tidal disruption to happen. Even if significant BH kicks are considered for a small fraction of NSBH binaries, the projected aligned spins of BHs are <jats:italic>χ</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub> ≳ 0.2. These systems can still be disrupted events unless the NSs are very massive. Thus, NS-first-born NSBH mergers would be promising multimessenger sources. We discuss various potential EM counterparts associated with these systems and their detectability in the upcoming fourth observation run.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Fast radio bursts (FRBs) are cosmological radio transients with an unclear generation mechanism. Known characteristics such as their luminosity, duration, spectrum, and repetition rate, etc., suggest that FRBs are powerful coherent radio signals at GHz frequencies, but the status of FRBs near the source remains unknown. As an extreme astronomical event, FRBs should be accompanied by energy-comparable or even more powerful X/<jats:italic>γ</jats:italic>-ray counterparts. Here, particle-in-cell simulations of ultrastrong GHz radio pulse interaction with GeV photons show that at ≳3 × 10<jats:sup>12</jats:sup> V cm<jats:sup>−1</jats:sup> field strengths, quantum cascade can generate dense pair plasmas, which greatly dampen the radio pulse. Thus, in the presence of GeV photons in the source region, GHz radio pulses stronger than 3 × 10<jats:sup>12</jats:sup> V cm<jats:sup>−1</jats:sup> cannot escape. This result indicates an upper field-strength limit of FRBs at the source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four of these systems, DW Cnc, V515 And, V1223 Sgr, and RX J2133.7+5107, we are able to perform timing analysis in and out of the low states. We find that, for DW Cnc and V515 And, the dominant periodicities in the light curves change as the flux decreases, indicating a change in the sources’ accretion properties as they transition to the low state. For V1223 Sgr, we find that the variability is almost completely quenched at the lowest flux, but we do not find evidence for a changing accretion geometry. For RX J2133.7+5107, the temporal properties do not change in the low state, but we do see a period of enhanced accretion that is coincident with increased variability on the beat frequency, which we do not associate with a change in the accretion mechanisms in the system.</jats:p>