Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering an active galactic nucleus (AGN). After studying the connection between major mergers and AGNs with the highest Eddington ratios at <jats:italic>z</jats:italic> = 2, we here expand our analysis to <jats:inline-formula> <jats:tex-math> <?CDATA $z\lt 0.2$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, exploring the same AGN parameter space. Using ESO VLT/FORS2 <jats:inline-formula> <jats:tex-math> <?CDATA $B-$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3eieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA $V-$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3eieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, and color images, we examine the morphologies of 17 galaxies hosting AGNs with Eddington ratios <jats:inline-formula> <jats:tex-math> <?CDATA ${\lambda }_{\mathrm{edd}}\gt 0.3$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3eieqn4.gif" xlink:type="simple" /> </jats:inline-formula>, and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. The combined sample of AGN and inactive galaxies was independently ranked by 19 experts with respect to the degree of morphological distortion. We combine the resulting individual rankings into multiple overall rankings, from which we derive the respective major merger fractions of the two samples. With a best estimate of <jats:italic>f</jats:italic> <jats:sub>m,agn</jats:sub> = 0.41 ± 0.12 for the AGN host galaxies and <jats:italic>f</jats:italic> <jats:sub>m,ina</jats:sub> = 0.08 ± 0.06 for the inactive galaxies, our results imply that our AGN host galaxies have a significantly higher merger rate, regardless of the observed wavelength or applied methodology. We conclude that although major mergers are an essential mechanism to trigger local high Eddington ratio AGNs at <jats:inline-formula> <jats:tex-math> <?CDATA $z\lt 0.2$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3eieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, the origin of <jats:inline-formula> <jats:tex-math> <?CDATA $\gtrsim 50 \% $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbd3eieqn6.gif" xlink:type="simple" /> </jats:inline-formula> of this specific AGN subpopulation still remains unclear.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Pulsar backend of the Canadian Hydrogen Intensity Mapping Experiment has monitored hundreds of known pulsars in the northern sky since fall 2018, providing a rich data set for the study of temporal variations in pulsar emission. Using a matched filtering technique, we report, for the first time, nulling behavior in five pulsars as well as mode switching in nine pulsars. Only one of the pulsars is observed to show both nulling and moding signals. These new nulling and mode-switching pulsars appear to come from a population with relatively long spin periods, in agreement with previous findings in the literature.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Although it has been shown that betatron and Fermi mechanisms contribute to electron acceleration at the dipolarization front (DF), the relative efficiency of these acceleration processes is unclear. In this paper, we directly calculate the electron adiabatic acceleration rate (the instantaneous acceleration) at DFs by using the data from the Magnetospheric Multiscale mission. We find that betatron acceleration dominates at the DF. Although the Fermi acceleration rate is smaller than the betatron acceleration rate, it is effective on a larger spatial scale than betatron acceleration, which is localized at the DF proper. The acceleration by the parallel electric field is negligible because it is far below the measurement uncertainties. The dependence of these acceleration rates on the DF normal, magnetic field, and thickness of the DF are analyzed. Our results provide important information for understanding the electron acceleration in the Earth's magnetotail.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The usage of the radius–luminosity (<jats:italic>R</jats:italic>–<jats:italic>L</jats:italic>) relation for the determination of black hole masses across the cosmic history, as well as its application for cosmological studies, motivates us to analyze its scatter, which has recently increased significantly for both the optical (H<jats:italic>β</jats:italic>) and UV (Mg <jats:sc>ii</jats:sc>) lines. To this purpose, we determined the scatter along the <jats:italic>R</jats:italic>–<jats:italic>L</jats:italic> relation for an up-to-date reverberation-mapped Mg <jats:sc>ii</jats:sc> sample. Studying linear combinations of the luminosity at 3000 Å with independent parameters such as the FWHM, the UV Fe <jats:sc>ii</jats:sc> strength (<jats:italic>R</jats:italic> <jats:sub>Fe <jats:sc>ii</jats:sc> </jats:sub>), and the fractional variability (<jats:italic>F</jats:italic> <jats:sub>var</jats:sub>) for the whole sample, we get only a small decrease in the scatter (<jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{\mathrm{rms}}=0.29\,-0.30$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> dex). Linear combinations with the dimensionless accretion rate (<jats:inline-formula> <jats:tex-math> <?CDATA $\dot{\,{ \mathcal M }}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) and the Eddington ratio lead to significant reductions of the scatter (<jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{\mathrm{rms}}\sim 0.1$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> dex), albeit both suffering from the interdependency on the observed time delay. After the division into two subsamples considering the median value of the <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{\,{ \mathcal M }}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> in the full sample, we find that the scatter decreases significantly for the highly accreting subsample. In particular, the smallest scatter of <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{\mathrm{rms}}=0.17$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> dex is associated with the independent parameter <jats:italic>R</jats:italic> <jats:sub>Fe <jats:sc>ii</jats:sc> </jats:sub>, followed by the combination with <jats:italic>F</jats:italic> <jats:sub>var</jats:sub> with <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{\mathrm{rms}}=0.19$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> dex. Both of these independent observationally inferred parameters are in turn correlated with <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{{ \mathcal M }}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb6f8ieqn8.gif" xlink:type="simple" /> </jats:inline-formula>. These results suggest that the large scatter along the <jats:italic>R</jats:italic>–<jats:italic>L</jats:italic> relation is driven <jats:italic>mainly</jats:italic> by the accretion rate intensity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analysis of the newly identified <jats:italic>μ</jats:italic> Tau Association (MUTA) of young stars at ≃150 pc from the Sun that is part of the large Cas-Tau structure, coeval and comoving with the <jats:italic>α</jats:italic> Persei cluster. This association is also located in the vicinity of the Taurus-Auriga star-forming region and the Pleiades association, although it is unrelated to them. We identify more than 500 candidate members of MUTA using Gaia DR2 data and the BANYAN Σ tool, and we determine an age of 62 ± 7 Myr for its population based on an empirical comparison of its color–magnitude diagram sequence with those of other nearby young associations. The MUTA association is related to the Theia 160 group of Kounkel &amp; Covey and corresponds to the e Tau group of Liu et al. It is also part of the Cas-Tau group of Blaauw. As part of this analysis, we introduce an iterative method based on spectral templates to perform an accurate correction of interstellar extinction of Gaia DR2 photometry, needed because of its wide photometric bandpasses. We show that the members of MUTA display an expected increased rate of stellar activity and faster rotation rates compared with older stars, and that literature measurements of the lithium equivalent width of nine G0- to K3-type members are consistent with our age determination. We show that the present-day mass function of MUTA is consistent with other known nearby young associations. We identify WD 0340+103 as a hot, massive white dwarf remnant of a B2 member that left its planetary nebula phase only 270,000 yr ago, posing an independent age constraint of <jats:inline-formula> <jats:tex-math> <?CDATA ${60}_{-6}^{+8}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb77eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Myr for MUTA, consistent with our isochrone age. This relatively large collection of comoving young stars near the Sun indicates that more work is required to unveil the full kinematic structure of the complex of young stars surrounding <jats:italic>α</jats:italic> Persei and Cas-Tau.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We estimate the strength of ram pressure stripping (RPS) for H<jats:sc>i</jats:sc>-rich galaxies in X-ray detected clusters. We find that galaxies under stronger RPS tend to show more significantly reduced total H<jats:sc>i</jats:sc> mass and enhanced central SFR when compared to control galaxies in the field that have similar stellar mass, stellar surface density and integral star formation rate. Galaxies under strong or weak RPS account for ∼40% of the H<jats:sc>i</jats:sc>-rich population at <jats:italic>R</jats:italic> <jats:sub>200</jats:sub>, and even beyond <jats:italic>R</jats:italic> <jats:sub>200</jats:sub> in the most massive clusters. Our results imply the important role of RPS as a channel of environmental processing far before the galaxies reach the core region of clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>W49B is the youngest supernova remnant (SNR) to date that exhibits recombining plasma. The two prevailing theories of this overionization are rapid cooling via adiabatic expansion or through thermal conduction with an adjacent cooler medium. To constrain the origin of the recombining plasma in W49B, we perform a spatially resolved spectroscopic study of deep XMM-Newton data across 46 regions. We adopt a three-component model (with one interstellar medium and two ejecta components), and we find that recombining plasma is present throughout the entire SNR, with increasing overionization from east to west. The latter result is consistent with previous studies, and we attribute the overionization in the west to adiabatic expansion. However, our findings depart from these prior works, as we find evidence of overionization in the east as well. As the SNR is interacting with molecular material there, we investigate the plausibility of thermal conduction as the origin of the rapid cooling. Based on estimated timescales, we show that both large- and small-scale thermal conduction can explain the observed overionization of the hotter ejecta. However, overionization of the cooler ejecta is only possible through small-scale thermal conduction resulting in evaporation of embedded, dense clouds with sizes ≲1 pc.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is well known that reverberation mapping of active galactic nuclei (AGNs) reveals a relationship between AGN luminosity and the size of the broad-line region, and that use of this relationship, combined with the Doppler width of the broad emission line, enables an estimate of the mass of the black hole at the center of the active nucleus based on a single spectrum. An unresolved key issue is the choice of parameter used to characterize the line width, either FWHM or line dispersion <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{\mathrm{line}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbc1cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (the square root of the second moment of the line profile). We argue here that use of FWHM introduces a bias, stretching the mass scale such that high masses are overestimated and low masses are underestimated. Here we investigate estimation of black hole masses in AGNs based on individual or “single-epoch” observations, with a particular emphasis in comparing mass estimates based on line dispersion and FWHM. We confirm the recent findings that, in addition to luminosity and line width, a third parameter is required to obtain accurate masses, and that parameter seems to be Eddington ratio. We present simplified empirical formulae for estimating black hole masses from the H<jats:italic>β</jats:italic> <jats:italic>λ</jats:italic>4861 and C <jats:sc>iv</jats:sc> <jats:italic>λ</jats:italic>1549 emission lines. While the AGN continuum luminosity at 5100 Å is usually used to predict the H<jats:italic>β</jats:italic> reverberation lag, we show that the luminosity of the H<jats:italic>β</jats:italic> broad component can be used instead without any loss of precision, thus eliminating the difficulty of accurately accounting for the host-galaxy contribution to the observed luminosity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery of a nuclear transient with the Caltech–NRAO Stripe 82 Survey (CNSS), a dedicated radio transient survey carried out with the Karl G. Jansky Very Large Array (VLA). This transient, CNSS J001947.3+003527, exhibited a turn-on over a timescale of ≲1 yr, increasing in flux density at 3 GHz from &lt;0.14 mJy in 2014 February to 4.4 ± 0.1 mJy in 2015 March, reaching a peak luminosity of <jats:inline-formula> <jats:tex-math> <?CDATA $5\times {10}^{28}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{Hz}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb94bieqn1.gif" xlink:type="simple" /> </jats:inline-formula> around 2015 October. The association of CNSS J0019+00 with the nucleus (Gaia and our very-long baseline interferometry positions are consistent to within 1 pc) of a nearby S0 Seyfert galaxy at 77 Mpc, together with the radio spectral evolution, implies that this transient is most likely a tidal disruption event (TDE). Our equipartition analysis indicates the presence of a ∼15,000 km s<jats:sup>−1</jats:sup> outflow, having energy ∼10<jats:sup>49</jats:sup> erg. We derive the radial density profile for the circumnuclear material in the host galaxy to be proportional to <jats:italic>R</jats:italic> <jats:sup>−2.5</jats:sup>. All of these properties suggest resemblance with radio-detected thermal TDEs like ASASSN-14li and XMMSL1 J0740-85. No significant X-ray or optical emission is detected from CNSS J0019+00, although this may simply be due to the thermal emission being weak during our late-time follow-up observations. From the CNSS survey we have obtained the first unbiased measurement of the rate of radio TDEs, <jats:italic>R</jats:italic>(&gt;500<jats:italic>μ</jats:italic>Jy) of about 2 × 10<jats:sup>−3</jats:sup> deg<jats:sup>−2</jats:sup>, or equivalently a volumetric rate of about 10 Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup>. This rate implies that all-sky radio surveys such as the VLA Sky Survey and those planned with ASKAP, will find many tens of radio TDEs over the next few years.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a new theory for the hierarchical clustering of dark matter (DM) halos, based on stochastic differential equations, that constitutes a change of perspective with respect to existing frameworks (e.g., the excursion set approach); this work is specifically focused on the halo mass function. First, we present a stochastic differential equation that describes fluctuations in the mass growth of DM halos, as driven by a multiplicative white (Gaussian) noise dependent on the spherical collapse threshold and on the power spectrum of DM perturbations. We demonstrate that such a noise yields an average drift of the halo population toward larger masses, that quantitatively renders the standard hierarchical clustering. Then, we solve the Fokker–Planck equation associated to the stochastic dynamics, and obtain the Press &amp; Schechter mass function as a (stationary) solution. Moreover, generalizing our treatment to a mass-dependent collapse threshold, we obtain an exact analytic solution capable of fitting remarkably well the <jats:italic>N</jats:italic>-body mass function over a wide range in mass and redshift. All in all, the new perspective offered by the theory presented here can contribute to a better understanding of the gravitational dynamics leading to the formation, evolution, and statistics of DM halos across cosmic times.</jats:p>