Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We study the probability distribution function (PDF) of relative velocity between two different dark matter halos (i.e., pairwise velocity) with high-resolution cosmological <jats:italic>N</jats:italic>-body simulations. We revisit a non-Gaussian framework to predict pairwise velocity statistics developed in Tinker. We investigate the pairwise velocity PDFs over a wide range of halo masses of 10<jats:sup>12.5</jats:sup> ≲ <jats:italic>M</jats:italic> [<jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>] ≲ 10<jats:sup>15</jats:sup> and redshifts of 0 &lt; <jats:italic>z</jats:italic> &lt; 1. At a given set of masses, redshift, and separation length between two halos, our model requires three parameters to set the pairwise velocity PDF, whereas previous non-Gaussian models in the literature assumed four or more free parameters. At length scales of 5 &lt; <jats:italic>r</jats:italic> [<jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> Mpc] &lt; 40, our model predicts the mean and dispersion of the pairwise velocity for dark matter halos with masses of 10<jats:sup>12.5</jats:sup> ≲ <jats:italic>M</jats:italic> [<jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>] ≲ 10<jats:sup>13.5</jats:sup> at 0.3 &lt; <jats:italic>z</jats:italic> &lt; 1 with a 5%-level precision. We demonstrate that our model of the pairwise velocity PDF provides an accurate mapping of the two-point clustering of massive-galaxy-sized halos at scales of <jats:italic>O</jats:italic>(10)<jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> Mpc between redshift and real space for a given real-space correlation function. For a mass-limited halo sample with masses greater than 10<jats:sup>13.5</jats:sup> <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at <jats:italic>z</jats:italic> = 0.55, our model can explain the monopole and quadrupole moments of the redshift-space two-point correlations with a precision better than 5% at the scales of 5−40 and 10–30 <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> Mpc, respectively. Our model of the pairwise velocity PDF will give a detailed explanation of the statistics of massive galaxies at intermediate scales in redshift surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar surface magnetic flux evolution plays a dominant role in the variability of total solar irradiance (TSI). Different proxies of magnetic activity have been introduced to correlate solar variability and TSI. We present the daily strong flux densities (SFDs) and weak flux densities (WFDs) defined with three magnetic thresholds calculated from the Solar Dynamic Observatory/Helioseismic Magnetic Imager. TSI measurements are from the radiometers of the Variability of Solar Irradiance and Gravity Oscillations experiment on the Solar and Heliosphere Observatory, and sunspot area (SSA) is from the National Oceanic and Atmospheric Administration. We characterize the influence of the magnetic flux density variation on the TSI using the Pearson, Spearman, and percentage bend correlations and wavelet analysis between the TSI and the flux density. The Pearson’s correlation shows that the TSI is negatively and strongly correlated with SFD and moderately with SSA; Spearman and 20% bend correlation shows that the TSI is moderately correlated with SFD and weakly with SSA on solar maximum, but weakly correlated on solar minimum. However, the TSI is not correlated with WFD during solar maximum and minimum. The bootstrapping tests also confirm that the influence of SFD on TSI is more significant than that of SSA. Finally, a wavelet analysis supports the idea that the SFD and TSI have a causality linkage and that the SFD dominantly influences the TSI variability on the rotational timescale.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The accumulation of aberrations along the optical path in a telescope produces distortions and speckles in the resulting images, limiting the performance of cameras at high angular resolution. It is important to achieve the highest possible sensitivity to faint sources, using both hardware and data analysis software. While analytic methods are efficient, real systems are better modeled numerically, but numerical models of complicated optical systems with many parameters can be hard to understand, optimize, and apply. Automatic differentiation or “backpropagation” software developed for machine-learning applications now makes calculating derivatives with respect to aberrations in arbitrary planes straightforward for any optical system. We apply this powerful new tool to the problem of high-angular-resolution astronomical imaging. Self-calibrating observables such as the “closure phase” or “bispectrum” have been widely used in optical and radio astronomy to mitigate optical aberrations and achieve high-fidelity imagery. Kernel phases are a generalization of closure phases valid in the limit of small phase errors. Using automatic differentiation, we reproduce existing kernel phase theory within this framework and demonstrate an extension to the case of a Lyot coronagraph, which is found to have self-calibrating combinations of speckles. which are resistant to phase noise, but only in the very high-wave-front-quality regime. As an illustrative example, we reanalyze Palomar adaptive optics observations of the binary <jats:italic>α</jats:italic> Ophiuchi, finding consistency between the new pipeline and the existing standard. We present a new Python package <jats:sc>morphine</jats:sc> that incorporates these ideas, with an interface similar to the popular package <jats:sc>poppy</jats:sc>, for optical simulation with automatic differentiation. These methods may be useful for designing improved astronomical optical systems by gradient descent.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The magnetic breakout model, in which reconnection in the corona leads to destabilization of a filament channel, explains numerous features of eruptive solar events, from small-scale jets to global-scale coronal mass ejections (CMEs). The underlying multipolar topology, pre-eruption activities, and sequence of magnetic-reconnection onsets (first breakout, then flare) of many observed fast CMEs/eruptive flares are fully consistent with the model. Recently, we demonstrated that most observed coronal-hole jets in fan/spine topologies also are induced by breakout reconnection at the null point above a filament channel (with or without a filament). For these two types of eruptions occurring in similar topologies, the key question is, why do some events generate jets while others form CMEs? We focused on the initiation of eruptions in large bright points/small active regions that were located in coronal holes and clearly exhibited null-point (fan/spine) topologies: such configurations are referred to as pseudostreamers. We analyzed and compared Solar Dynamics Observatory/Atmospheric Imaging Assembly, Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment, and Reuven Ramaty High Energy Solar Spectroscopic Imager observations of three events. Our analysis of the events revealed two new observable signatures of breakout reconnection prior to the explosive jet/CME outflows and flare onset: coronal dimming and the opening up of field lines above the breakout current sheet. Most key properties were similar among the selected erupting structures, thereby eliminating region size, photospheric field strength, magnetic configuration, and pre-eruptive evolution as discriminating factors between jets and CMEs. We consider the factors that contribute to the different types of dynamic behavior, and conclude that the main determining factor is the ratio of the magnetic free energy associated with the filament channel compared to the energy associated with the overlying flux inside and outside the pseudostreamer dome.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analysis of the optical properties of three Ultra Luminous X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from the George Mitchel spectrograph in the context of the Metal-THINGS survey. The optical properties for ULX-1 and ULX-3 are presented, while the spaxel associated with ULX-2 had a low S/N, which prevented its analysis. We also report the kinematics and dimensions of the optical nebula associated with each ULX using ancillary data from the PUMA Fabry–Perot spectrograph. A BPT analysis demonstrates that most spaxels in NGC 925 are dominated by star-forming regions, including those associated with ULX-1 and ULX-3. Using the resolved gas-phase metallicities, a negative metallicity gradient is found, consistent with previous results for spiral galaxies, while the ionization parameter tends to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very low gas metallicity for its galactocentric distance, identified by two independent methods, while exhibiting a typical ionization. We find that such low gas metallicity is best explained in the context of the high-mass X-ray binary population, where the low-metallicity environment favors active Roche lobe overflows that can drive much higher accretion rates. An alternative scenario invoking accretion of a low-mass galaxy is not supported by the data in this region. Finally, ULX-3 shows both a high metallicity and ionization parameter, which is consistent with the progenitor being a highly accreting neutron star within an evolved stellar population region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 8<jats:sub>27</jats:sub> − 7<jats:sub>34</jats:sub> transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12 m telescope along with the 22 GHz transition using the Effelsberg 100 m telescope. We have used a simple model to analyze the multitransition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: <jats:italic>n</jats:italic>(H<jats:sub>2</jats:sub>O)/<jats:italic>n</jats:italic>(H<jats:sub>2</jats:sub>) = 1.4–2.5 × 10<jats:sup>−4</jats:sup>. For <jats:italic>o</jats:italic> Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor ∼1.6–3. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations; such discrepancies are perhaps unsurprising given the exponential nature of maser amplification.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the stellar populations of passive spiral galaxies as a function of mass and environment, using integral field spectroscopy data from the Sydney-AAO Multi-object Integral field spectrograph Galaxy Survey. Our sample consists of 52 cluster passive spirals and 18 group/field passive spirals, as well as a set of S0s used as a control sample. The age and [Z/H] estimated by measuring Lick absorption line strength indices both at the center and within 1<jats:italic>R</jats:italic> <jats:sub>e</jats:sub> do not show a significant difference between the cluster and the field/group passive spirals. However, the field/group passive spirals with log(<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) ≳ 10.5 show decreasing [<jats:italic>α</jats:italic>/Fe] along with stellar mass, which is ∼0.1 dex smaller than that of the cluster passive spirals. We also compare the stellar populations of passive spirals with S0s. In the clusters, we find that passive spirals show slightly younger age and lower [<jats:italic>α</jats:italic>/Fe] than the S0s over the whole mass range. In the field/group, stellar populations show a similar trend between passive spirals and S0s. In particular, [<jats:italic>α</jats:italic>/Fe] of the field/group S0s tend to be flattening with increasing mass above log(<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) ≳ 10.5, similar to the field/group passive spirals. We relate the age and [<jats:italic>α</jats:italic>/Fe] of passive spirals to their mean infall time in phase space; we find a positive correlation, in agreement with the prediction of numerical simulations. We discuss the environmental processes that can explain the observed trends. The results lead us to conclude that the formation of the passive spirals and their transformation into S0s may significantly depend on their environments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions. We carried out a combined analysis of the data obtained by more recent major observations of this source—two observations performed by XMM-Newton in 2000 and 2006 and six observations performed by Suzaku in 2008. A unified model, which is consistent with all eight of the observations by the two satellites with large intensity and spectral changes, was constructed. The model consists of a hard power law with the spectral index of Γ<jats:sub>Hard</jats:sub> = 1.4–1.7, which is interpreted as the Comptonized emission from the corona above an accretion disk. In the high-flux states, an additional soft excess component dominates, which is consistent with a model with either a steeper power law with Γ<jats:sub>Soft</jats:sub> = 3.3–3.85 or the warm Comptonization component. These emissions from the central engine are absorbed by a partial covering material and warm absorbers. A reflection component and several emission lines are also present. We examined the relationship between the intrinsic luminosity and the absorbers’ physical parameters such as the column density, which suggests that the source expanded significantly during the bright states when the soft excess is greatly enhanced.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine the three-dimensional structure and dust extinction properties in a ∼200 pc × 100 pc region in the southwest bar of the Small Magellanic Cloud (SMC). We model a deep Hubble Space Telescope optical color–magnitude diagram (CMD) of red clump and red giant branch stars in order to infer the dust extinction and galactic structure. We model the distance distribution of the stellar component with a Gaussian and find a centroid distance of 65.2 kpc (distance modulus <jats:italic>μ</jats:italic> = 19.07 mag) with an FWHM  ≈ 11.3 kpc. This large extent along the line of sight reproduces results from previous studies using variable stars and red clump stars. Additionally, we find an offset between the stellar and dust distributions, with the dust on the near side relative to the stars by 3.22 <jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-1.44}^{+1.69}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc48bieqn1.gif" xlink:type="simple" /> </jats:inline-formula> kpc, resulting in a 73% reddened fraction of stars. Modeling the dust layer with a log-normal <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> distribution indicates a mean extinction 〈<jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>〉 = 0.41 ± 0.09 mag. We also calculate <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>/<jats:italic>N</jats:italic> <jats:sub> <jats:italic>H</jats:italic> </jats:sub> =  3.2–4.2 × 10<jats:sup>−23</jats:sup> mag cm<jats:sup>2</jats:sup> H<jats:sup>−1</jats:sup>, which is significantly lower than the Milky Way value but is comparable to previous SMC dust-to-gas ratio measurements. Our results yield the first joint dust extinction and 3D geometry properties in a key region in the SMC. This study demonstrates that CMD modeling can be a powerful tool to simultaneously constrain dust extinction and geometry properties in nearby galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first mid-infrared (MIR) detections of HNC and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}^{13}\mathrm{CN}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca36ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in the interstellar medium, and numerous resolved HCN rovibrational transitions. Our observations span 12.8–22.9 <jats:italic>μ</jats:italic>m toward the hot core Orion IRc2, obtained with the Echelon-Cross-Echelle Spectrograph aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). In particular, ∼5 km s<jats:sup>−1</jats:sup> resolution distinguishes individual rovibrational transitions of the HNC and HCN P, Q, and R branches; and the <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}^{13}\mathrm{CN}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca36ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> R branch. This allows direct measurement of the species’ excitation temperatures, column densities, and relative abundances. HNC and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}^{13}\mathrm{CN}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca36ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> exhibit a local standard of rest velocity of −7 km s<jats:sup>−1</jats:sup> that may be associated with an outflow from nearby radio source I and an excitation temperature of about 100 K. We resolve two velocity components for HCN, the primary component also being at −7 km s<jats:sup>−1</jats:sup> with a temperature of 165 K. The hottest component, which had never before been observed, is at 1 km s<jats:sup>−1</jats:sup> with a temperature of 309 K. This is the closest component to the hot core’s center measured to date. The derived <jats:inline-formula> <jats:tex-math> <?CDATA ${}^{12}{\rm{C}}{/}^{13}{\rm{C}}=13\pm 2$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca36ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> is below expectation for Orion’s Galactocentric distance, but the derived HCN/HNC = 72 ± 7 is expected for this extreme environment. Compared to previous sub-millimeter and millimeter observations, our SOFIA line survey of this region shows that the resolved MIR molecular transitions are probing a distinct physical component and isolating the chemistry closest to the hot core.</jats:p>