Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Massive molecular gas has been discovered in giant elliptical galaxies at the centers of galaxy clusters. To reveal its role in active galactic nucleus (AGN) feedback in those galaxies, we construct a semianalytical model of gas circulation. This model especially focuses on the massive molecular gas (interstellar cold gas on a scale of ∼10 kpc) and the circumnuclear disk (≲0.5 kpc). We consider the destruction of the interstellar cold gas by star formation and the gravitational instability for the circumnuclear disk. Our model can reproduce the basic properties of the interstellar cold gas and the circumnuclear disk, such as their masses. We also find that the circumnuclear disk tends to stay at the boundary between stable and unstable states. This works as an “adjusting valve” that regulates mass accretion toward the supermassive black hole. On the other hand, the interstellar cold gas serves as a “fuel tank” in the AGN feedback. Even if the cooling of the galactic hot gas is prevented, the interstellar cold gas can sustain the AGN activity for ≳0.5 Gyr. We also confirm that the small entropy of hot gas (≲30 keV cm<jats:sup>2</jats:sup>) or the short cooling time (≲1 Gyr) is a critical condition for the existence of massive amounts of molecular gas in the galaxy. The dissipation time of the interstellar cold gas may be related to the critical cooling time. The galaxy behavior is described by a simple relation among the disk stability, the cloud dissipation time, and the gas cooling rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We studied an Earth-directed coronal mass ejection (CME) that erupted on 2015 March 15. Our aim was to model the CME flux rope as a magnetized structure using the European Heliospheric Forecasting Information Asset (EUHFORIA). The flux rope from eruption data (FRED) output was applied to the EUHFORIA spheromak CME model. In addition to the geometrical properties of the CME flux rope, we needed to input the parameters that determine the CME internal magnetic field like the helicity, tilt angle, and toroidal flux of the CME flux rope. According to the FRED technique geometrical properties of the CME flux rope are obtained by applying a graduated cylindrical shell fitting of the CME flux rope on the coronagraph images. The poloidal field magnetic properties can be estimated from the reconnection flux in the source region utilizing the post-eruption arcade method, which uses the Heliospheric Magnetic Imager magnetogram together with the Atmospheric Imaging Assembly (AIA) 193 Å images. We set up two EUHFORIA runs with RUN-1 using the toroidal flux obtained from the FRED technique and RUN-2 using the toroidal flux that was measured from the core dimming regions identified from the AIA 211 Å images. We found that the EUHFORIA simulation outputs from RUN-1 and RUN-2 are comparable to each other. Overall using the EUHFORIA spheromak model, we successfully obtained the magnetic field rotation of the flux rope, while the arrival time near Earth and the strength of the interplanetary CME magnetic field at Earth are not as accurately modeled.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Reconnection fronts (RFs) play a vital role in particle acceleration and energy transport in the terrestrial magnetosphere. It is widely believed that RFs have planar monotonic profiles that determine the particle dynamics. However, recent in situ studies have revealed that the front surface is not planar as expected but rather rippled. How the surface irregularities of RFs’ impact particle energization and transport is still an open issue. Using a particle-tracing technique, we traced the trajectories of ions near fronts with or without surface ripples at different scales to understand how ions are mediated by such rippled structures. We find that the ion relative energy gain increases considerably when the rippled surface of RFs appears. The main acceleration mechanism is ion-trapping acceleration, in which ions are confined at the RFs for a longer time by the rippled structure and are accelerated by the duskward electric field. Moreover, ions can be accelerated effectively when their gyroradius is comparable to the size of the ripple. Formulas of relative energy gain as a function of the ripple size are presented.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Although galactic outflows play a key role in our understanding of the evolution of galaxies, the exact mechanism by which galactic outflows are driven is still far from being understood and, therefore, our understanding of associated feedback mechanisms that control the evolution of galaxies is still plagued by many enigmas. In this work, we present a simple toy model that can provide insight on how non-axisymmetric instabilities in galaxies (bars, spiral arms, warps) can lead to local exponential magnetic field growth by radial flows beyond the equipartition value by at least two orders of magnitude on a timescale of a few 100 Myr. Our predictions show that the process can lead to galactic outflows in barred spiral galaxies with a mass-loading factor <jats:italic>η</jats:italic> ≈ 0.1, in agreement with our numerical simulations. Moreover, our outflow mechanism could contribute to an understanding of the large fraction of barred spiral galaxies that show signs of galactic outflows in the <jats:sc>chang-es</jats:sc> survey. Extending our model shows the importance of such processes in high-redshift galaxies by assuming equipartition between magnetic energy and turbulent energy. Simple estimates for the star formation rate in our model together with cross correlated masses from the star-forming main sequence at redshifts <jats:italic>z</jats:italic> ∼ 2 allow us to estimate the outflow rate and mass-loading factors by non-axisymmetric instabilities and a subsequent radial inflow dynamo, giving mass-loading factors of <jats:italic>η</jats:italic> ≈ 0.1 for galaxies in the range of <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> = 10<jats:sup>9</jats:sup>–10<jats:sup>12</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, in good agreement with recent results of <jats:sc>sinfoni</jats:sc> and <jats:sc>kmos</jats:sc> <jats:sup>3D</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hypervelocity impacts on spacecraft surfaces produce a wide range of effects including transient plasma clouds, surface material ablation, and for some impacts, the liberation of spacecraft material as debris clouds. This study examines debris-producing impacts on the Parker Solar Probe spacecraft as it traverses the densest part of the zodiacal cloud: the inner heliosphere. Hypervelocity impacts by interplanetary dust grains on the spacecraft that produce debris clouds are identified and examined. Impact-generated plasma and debris strongly perturb the near-spacecraft environment, producing distinct signals on electric, magnetic, and imaging sensors, as well as anomolous behavior of the star tracker cameras used for attitude determination. From these data, the spatial distribution, mass, and velocity of impactors that produce debris clouds are estimated. Debris-cloud expansion velocity and debris fragment sizes are constrained by the observational data, and long-duration electric potential perturbations caused by debris clouds are reported, along with a hypothesis for their creation. Impact-generated plasma-cloud expansion velocities, as well as pickup acceleration by the solar wind and driven plasma waves are also measured. Together, these observations produce a comprehensive picture of near-spacecraft environmental perturbations in the aftermath of a hypervelocity impact.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of the orbital light curves of the recurrent nova IM Normae since its 2002 outburst. The broad “eclipses” recur with a 2.46 hr period, which increases on a timescale of 1.28(16) × 10<jats:sup>6</jats:sup> yr. Under the assumption of conservative mass transfer, this suggests a rate near 10<jats:sup>−7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>, and this agrees with the estimated <jats:italic>accretion</jats:italic> rate of the postnova, based on our estimate of luminosity. IM Nor appears to be a close match to the famous recurrent nova T Pyxidis. Both stars appear to have very high accretion rates, sufficient to drive the recurrent-nova events. Both have quiescent light curves, which suggest strong heating of the low-mass secondary, and very wide orbital minima, which suggest obscuration of a large “corona” around the primary. And both have very rapid orbital period increases, as expected from a short-period binary with high mass transfer from the low-mass component. These two stars may represent a final stage of nova—and cataclysmic variable—evolution, in which irradiation-driven winds drive a high rate of mass transfer, thereby evaporating the donor star in a paroxysm of nova outbursts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Population III stars ended the cosmic dark ages and began early cosmological reionization and chemical enrichment. However, in spite of their importance to the evolution of the early universe, their properties remain uncertain because of the limitations on previous numerical simulations and the lack of any observational constraints. Here, we investigate Population III star formation in five primordial halos using 3D radiation-hydrodynamical cosmological simulations. We find that multiple stars form in each minihalo and that their numbers increase over time, with up to 23 stars forming in one of the halos. Radiative feedback from the stars generates strong outflows, deforms the surrounding protostellar disk, and delays star formation for a few thousand years. Star formation rates vary with halo, and depend on the mass accretion onto the disk, the halo spin number, and the fraction of massive stars in the halo. The stellar masses in our models range from 0.1–37 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and of the 55 stars that form in our models, 12 are &gt;10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and most of the others are 1–10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Our simulations thus suggest that Population III stars have characteristic masses of 1–10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and top-heavy initial mass functions with dN/dM <jats:inline-formula> <jats:tex-math> <?CDATA $\propto \,{M}_{* }^{-1.18}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∝</mml:mo> <mml:mspace width="0.50em" /> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.18</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3916ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Up to 70% of the stars are ejected from their disks by three-body interactions that, along with ionizing UV feedback, limit their final masses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the response of a starved Kerr black hole magnetosphere to abrupt changes in the intensity of disk emission and in the global magnetospheric current, by means of one-dimensional general relativistic particle-in-cell simulations. Such changes likely arise from the intermittency of the accretion process. We find that in cases where the pair-production opacity contributed by the soft disk photons is modest, as in, e.g., M87, such changes can give rise to delayed, strong teraelectronvolt (TeV) flares, dominated by curvature emission of particles accelerated in the gap. The flare rise time, and the delay between the external variation and the onset of the flare emitted from the outer gap boundary, are of the order of the light-crossing time of the gap. The rapid, large-amplitude TeV flares observed in M87, and perhaps, other active galactic nuclei may be produced by such a mechanism.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In recent years, continuum-reverberation mapping involving high-cadence UV/optical monitoring campaigns of nearby active galactic nuclei has been used to infer the size of their accretion disks. One of the main results from these campaigns has been that in many cases the accretion disks appear too large, by a factor of 2–3, compared to standard models. Part of this may be due to diffuse continuum emission from the broad-line region (BLR), which is indicated by excess lags around the Balmer jump. Standard cross-correlation lag-analysis techniques are usually used to just recover the peak or centroid lag and cannot easily distinguish between reprocessing from the disk and BLR. However, frequency-resolved lag analysis, where the lag is determined at each Fourier frequency, has the potential to separate out reprocessing on different size scales. Here we present simulations to demonstrate the potential of this method and then apply a maximum-likelihood approach to determine frequency-resolved lags in NGC 5548. We find that the lags in NGC 5548 generally decrease smoothly with increasing frequency, and are not easily described by accretion-disk reprocessing alone. The standard cross-correlation lags are consistent with lags at frequencies lower than 0.1 day<jats:sup>−1</jats:sup>, indicating they are dominated from reprocessing at size scales greater than ∼10 light days. A combination of a more distant reprocessor, consistent with the BLR, along with a standard-sized accretion disk is more consistent with the observed lags than a larger disk alone.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We calculate the Galactic Chemical Evolution of Mo and Ru by taking into account the contribution from <jats:italic>ν</jats:italic> <jats:italic>p</jats:italic>-process nucleosynthesis. We estimate yields of <jats:italic>p</jats:italic>-nuclei such as <jats:sup>92,94</jats:sup>Mo and <jats:sup>96,98</jats:sup>Ru through the <jats:italic>ν</jats:italic> <jats:italic>p</jats:italic>-process in various supernova progenitors based upon recent models. In particular, the <jats:italic>ν</jats:italic> <jats:italic>p</jats:italic>-process in energetic hypernovae produces a large amount of <jats:italic>p</jats:italic>-nuclei compared to the yield in ordinary core-collapse SNe. Because of this, the abundances of <jats:sup>92,94</jats:sup>Mo and <jats:sup>96,98</jats:sup>Ru in the Galaxy are significantly enhanced at [Fe/H] = 0 by the <jats:italic>ν</jats:italic> <jats:italic>p</jats:italic>-process. We find that the <jats:italic>ν</jats:italic> <jats:italic>p</jats:italic>-process in hypernovae is the main contributor to the elemental abundance of <jats:sup>92</jats:sup>Mo at low metallicity [Fe/H] &lt; −2. Our theoretical prediction of the elemental abundances in metal-poor stars becomes more consistent with observational data when the <jats:italic>ν</jats:italic> <jats:italic>p</jats:italic>-process in hypernovae is taken into account.</jats:p>