Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Fluctuation dynamos are thought to play an essential role in the evolution of magnetized galaxies, saturating within ∼0.01 Gyr and thus potentially acting as seeds for large-scale mean-field dynamos. However, unambiguous observational confirmation of the fluctuation dynamo action in a galactic environment is still missing. This is because, in spiral galaxies, it is difficult to differentiate between small-scale magnetic fields generated by a fluctuation dynamo and those due to the tangling of the large-scale field. We propose that observations of magnetic fields in elliptical galaxies would directly probe the fluctuation dynamo action. This is motivated by the fact that in ellipticals, due to their lack of significant rotation, the conventional large-scale dynamo is absent and the fluctuation dynamo is responsible for controlling the strength and structure of the magnetic field. By considering turbulence injected by Type Ia supernova explosions and possible magnetic field amplification by cooling flows, we estimate expected magnetic field strengths of <jats:inline-formula> <jats:tex-math> <?CDATA $0.2\mbox{--}1\,\mu {\rm{G}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd2bbieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in the centers of quiescent elliptical galaxies. We use a semianalytic model of galaxy formation to estimate the distribution and redshift evolution of field strengths, tentatively finding a decrease in magnetic field strength with decreasing redshift. We analyze a historical sample of radio sources that exhibit the Laing–Garrington effect (radio polarization asymmetry in jets) and infer magnetic field strengths between <jats:inline-formula> <jats:tex-math> <?CDATA $0.14\,\mathrm{and}\,1.33\,\mu {\rm{G}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd2bbieqn2.gif" xlink:type="simple" /> </jats:inline-formula> for a uniform thermal electron density and between <jats:inline-formula> <jats:tex-math> <?CDATA $1.36\,\mathrm{and}\,6.21\,\mu {\rm{G}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd2bbieqn3.gif" xlink:type="simple" /> </jats:inline-formula> for the thermal electron density following the King profile. We examine observational techniques for measuring the magnetic field saturation state in elliptical galaxies, focusing on Faraday rotation measure grids, the Laing–Garrington effect, synchrotron emission, and gravitational lensing, and finding appealing prospects for future empirical analysis.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many core-collapse supernova (SN) progenitors show indications of enhanced pre-SN mass loss and outbursts, some of which could be powered by wave energy transport within the progenitor star. Depending on the star’s structure, convectively excited waves driven by late-stage nuclear burning can carry substantial energy from the core to the envelope, where the wave energy is dissipated as heat. We examine the process of wave energy transport in single-star SNe progenitors with masses between 11 and 50 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Using MESA stellar evolution simulations, we evolve stars until core collapse and calculate the wave power produced and transmitted to the stars’ envelopes. These models improve upon prior efforts by incorporating a more realistic wave spectrum and nonlinear damping effects, reducing our wave-heating estimates by ∼1 order of magnitude compared to prior work. We find that waves excited during oxygen/neon burning typically transmit ∼10<jats:sup>46</jats:sup>–10<jats:sup>47</jats:sup> erg of energy at 0.1–10 yr before core collapse in typical (<jats:italic>M</jats:italic> &lt; 30 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) SN progenitors. High-mass progenitors can often transmit ∼10<jats:sup>47</jats:sup>–10<jats:sup>48</jats:sup> erg of energy during oxygen/neon burning, but this tends to occur later, at about 0.01–0.1 yr before core collapse. Pre-SN outbursts may be most pronounced in low-mass SN progenitors (<jats:italic>M</jats:italic> ≲ 12 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) undergoing semidegenerate neon ignition and in high-mass progenitors (<jats:italic>M</jats:italic> ≳ 30 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) exhibiting convective shell mergers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present ultradeep, matched-resolution Karl G. Jansky Very Large Array observations at 10 and 3 GHz in the COSMOS field: the COSMOS-XS survey. The final 10 and 3 GHz images cover ∼16 and <jats:inline-formula> <jats:tex-math> <?CDATA $\sim 180\,{\mathrm{arcmin}}^{2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and reach median rms values at the phase center of 0.41 and 0.53 <jats:italic>μ</jats:italic>Jy beam<jats:sup>−1</jats:sup>, respectively. Both images have an angular resolution of  ∼20. To account for the spectral shape and resolution variations across the broad bands, we image all data with a multiscale, multifrequency synthesis algorithm. We present source catalogs for the 10 and 3 GHz image with 91 and 1498 sources, respectively, above a peak brightness threshold of 5<jats:italic>σ</jats:italic>. We present source counts with completeness corrections included that are computed via Monte Carlo simulations. Our corrected counts at 3 GHz are consistent within the uncertainties with other results at 3 and 1.4 GHz but extend to fainter flux densities than previous direct detections. The 3 GHz number counts exceed the counts predicted by the semiempirical simulations developed in the framework of the SKA Simulated Skies project, consistent with previous <jats:italic>P</jats:italic>(<jats:italic>D</jats:italic>) analyses. Our source counts suggest a steeper luminosity function evolution for faint star-forming sources. The semiempirical Tiered Radio Extragalactic Continuum Simulation predicts this steeper evolution and is in better agreement with our results at 10 and 3 GHz within the expected variations from cosmic variance. In summary, the multiband, matched-resolution COSMOS-XS survey in the COSMOS field provides a high-resolution view of the ultrafaint radio sky that can help guide next-generation radio facilities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>By employing our charge-consistent acceleration model we demonstrate a possibility to explain the isotopic ratios observed in a number of <jats:sup>3</jats:sup>He-rich events. We investigate the dependence of isotopic ratios of heavy ions on the energy of the particles, the acceleration efficiency, the product of acceleration time, and the number density of ambient electrons, of the plasma temperature, and of the spectral index of the magnetic fluctuations by which the ions are energized in the acceleration region. On the basis of the energy spectra of heavy ions and their isotopic ratios observed in the event of 2002 August 20 by the Solar Isotope Spectrometer on board the Advanced Composition Explorer (SIS/ACE) we put constraints on the plasma parameters in the acceleration region. Our investigation gives evidence that the spectral index of the fluctuations with which the ions interact is greater than 2, and that the plasma temperature is about 1 MK.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The correlation between black hole mass and the stellar mass of the bulge of the host galaxy has attracted much attention ever since its discovery. While traditional investigations of this correlation have treated elliptical galaxies as single, monolithic spheroids, the recent realization that massive elliptical galaxies have undergone significant late-time (<jats:inline-formula> <jats:tex-math> <?CDATA $z\lesssim 2$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) dissipationless assembly since their initially dense “red nugget” phase strongly suggests that black holes in present-day ellipticals should be associated only with their cores and not with their extended envelopes. We perform two-dimensional image decomposition of Two Micron All Sky Survey <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>-band images to derive the stellar mass of the cores of 35 nearby ellipticals with reliably measured black hole masses. We revisit the relation between black hole mass and bulge stellar mass by combining classical bulges with the cores of ellipticals. The new relation exhibits nearly identical slope (<jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\bullet }\propto {M}_{\mathrm{core}}^{1.2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) as the conventional relation but a factor of ∼2 higher normalization and moderately larger intrinsic scatter (0.4 dex). At a core mass of <jats:inline-formula> <jats:tex-math> <?CDATA ${10}^{11}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\bullet }/{M}_{\mathrm{core}}=0.9 \% $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>, but it rises to <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\bullet }/{M}_{\mathrm{core}}=1.5 \% $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> for the most massive cores with mass <jats:inline-formula> <jats:tex-math> <?CDATA ${10}^{12}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. Fast and slow rotator ellipticals follow the same correlation. The <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\bullet }\mbox{--}{M}_{\mathrm{core}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcaa1ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> relation provides a revised benchmark for studies of black hole–galaxy coevolution in the high-redshift universe.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{O}}\,{\rm\small{VI}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> absorption in the circumgalactic medium (CGM) as a function of projected virial radius and azimuthal angle. We compare these simulations to an observed sample of 53 galaxies from the Multiphase Galaxy Halos Survey. Using <jats:sc>Mockspec</jats:sc>, an absorption-line analysis pipeline, we generate synthetic quasar absorption-line observations of the simulated CGM. To best emulate observations, we studied the averaged properties of 15,000 “mock samples,” each of 53 sight lines having a distribution of <jats:inline-formula> <jats:tex-math> <?CDATA $D/{R}_{\mathrm{vir}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and sight-line orientation statistically consistent with the observations. We find that the <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{O}}\,{\rm\small{VI}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo (<jats:inline-formula> <jats:tex-math> <?CDATA $D/{R}_{\mathrm{vir}}\leqslant 0.375$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>) and is within 1.1<jats:italic>σ</jats:italic> in the outer halo (<jats:inline-formula> <jats:tex-math> <?CDATA $D/{R}_{\mathrm{vir}}\gt 0.75$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>), but is underproduced within <jats:inline-formula> <jats:tex-math> <?CDATA $0.375\lt D/{R}_{\mathrm{vir}}\leqslant 0.75$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. The observed bimodal distribution of the <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{O}}\,{\rm\small{VI}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> covering fraction with azimuthal angle, showing a higher frequency of absorption along the projected major and minor axes of galaxies, is not reproduced in the simulations. Further analysis reveals the spatial-kinematic distribution of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{O}}\,{\rm\small{VI}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd033ieqn8.gif" xlink:type="simple" /> </jats:inline-formula>-absorbing gas is dominated by outflows in the inner halo mixed with an inflowing gas that originates from farther out in the halo. Though the CGM of the individual simulated galaxies exhibits spatial structure, the flat azimuthal distribution occurs because the individual simulated galaxies do not develop a CGM structure that is universal from galaxy to galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Cosmic-ray (CR) fluxes in the heliosphere are affected by the transient interplanetary coronal mass ejections (ICMEs), causing so-called Forbush decreases (FDs), characterized by a decline of up to 25% in the neutron monitor counts at the Earth’s surface, lasting up to over a week. FDs are thought to be caused by the ICME shock wave or the magnetic flux rope embedded in the ICME inhibiting CR propagation through the ICME structure. FDs are typically modeled as enhanced diffusion within the ICME structure. However, so far modeling has not considered the access of the CRs from the interplanetary field lines into the isolated magnetic field lines of the ICME flux rope. We study the effect of an ICME flux rope on particle propagation by using full-orbit particle simulations, with the interface between the external interplanetary magnetic field and the isolated flux rope field lines modeled analytically. We find that the particles can access the flux rope through the x-point region, where the external magnetic fields cancel the azimuthal component of the rope field. The transport through this region is fast compared to diffusive radial propagation within the rope. As a result, the propagation of CRs into the flux rope can be modeled as diffusion into a cylinder. The density cavity within the rope is asymmetric, and limited to the magnetic field lines isolated from the external field. Thus, in order to evaluate the role of the flux rope in FDs, one must analyze the extent of the region where the flux rope magnetic field lines are separated from the interplanetary magnetic fields.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Understanding the Fe <jats:sc>II</jats:sc> emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as “Eigenvector 1” and tracing the chemical evolution of the cosmos. Recently, three large Fe <jats:sc>II</jats:sc> atomic data sets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code <jats:sc>Cloudy</jats:sc> and examined predictions using a new generation of AGN spectral energy distribution (SED), which indicates that the ultraviolet (UV) emission can be quite different depending on the data set utilized. The Smyth et al. data set better reproduces the observed Fe <jats:sc>II</jats:sc> template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of ≈100 km s<jats:sup>−1</jats:sup> reproduces the observed shape and strength of the so-called Fe <jats:sc>II</jats:sc> “UV bump.” Comparing our predictions to the observed Fe <jats:sc>II</jats:sc> template, we derive a typical cloud density of 10<jats:sup>11</jats:sup> cm<jats:sup>−3</jats:sup> and photon flux of 10<jats:sup>20</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, and show that these largely reproduce the observed Fe <jats:sc>II</jats:sc> emission in the UV and optical. We calculate the <jats:italic>I</jats:italic>(Fe <jats:sc>II</jats:sc>)/<jats:italic>I</jats:italic>(Mg <jats:sc>II</jats:sc>) emission-line intensity ratio using our best-fitting model and obtain log(<jats:italic>I</jats:italic>(Fe <jats:sc>II</jats:sc>)/<jats:italic>I</jats:italic>(Mg <jats:sc>II</jats:sc>)) ∼  0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The dynamical evolution of protoplanetary disks is of key interest for building a comprehensive theory of planet formation and to explain the observational properties of these objects. Using the magnetohydrodynamics code Athena++, with an isothermal shearing box setup, we study the boundary between the active and dead zone, where the accretion rate changes and mass can accumulate. We quantify how the turbulence level is affected by the presence of a non-uniform Ohmic resistivity in the radial <jats:italic>x</jats:italic> direction that leads to a region of inhibited turbulence (or dead zone). Comparing the turbulent activity to that of ideal simulations, the turbulence-inhibited area shows density fluctuations and magnetic activity at its boundaries, driven by energy injection from the active (ideal) zone boundaries. We find magnetic dissipation to be significantly stronger in the ideal regions, and the turbulence penetration through the boundary of the dead zone is determined by the value of the resistivity itself, through the Ohmic dissipation process, though the thickness of the transition does not play a significant role in changing the dissipation. We investigate the 1D spectra along the shearing direction: magnetic spectra appear flat at large scales both in ideal as well as resistive simulations, though a Kolmogorov scaling over more than one decade persists in the dead zone, suggesting the turbulent cascade is determined by the hydrodynamics of the system: magnetorotational instability dynamo action is inhibited where sufficiently high resistivity is present.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The unusual behavior of the spectral lines of NGC5548 during the STORM campaign demonstrated a missing piece in the structure of AGNs. For a two-month period in the middle of the campaign, the spectral lines showed a deficit in flux and a reduced response to the variations of the UV continuum. This was the first time that this behavior was unequivocally observed in an AGN. Our previous papers explained this as being due to a variable disk wind that acts as a shield and alters the SED. Here, we use Cloudy to create an atlas of photoionization models for a variety of disk winds, in order to study their effects on the SED. We show that the winds have three different cases: Case 1 winds are transparent, fully ionized, and have minimal effects on the intrinsic SED, although they can produce some line emission, especially He <jats:sc>ii</jats:sc> or FeK<jats:italic>α</jats:italic>. We propose that this is the situation in most of the AGNs. Case 2 winds, which have a He<jats:sup>++</jats:sup>–He<jats:sup>+</jats:sup> ionization front, block part of the XUV continuum but transmit much of the Lyman continuum. They lead to the observed abnormal behavior. Case 3 winds have a H<jats:sup>+</jats:sup> ionization front and block much of the Lyman continuum. The results show that the presence of these winds has important effects on the spectral lines of AGNs. They will thus have an effect on the measurements of the black hole mass and the geometry of the AGN. This atlas of spectral simulations can serve as a guide to future reverberation campaigns.</jats:p>