Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The symmetry axes of active galactic nuclei (AGNs) are randomly distributed in space, but highly inclined sources are heavily obscured and are not seen as quasars with broad emission lines. The obscuring torus geometry determines the average viewing angle, and if the torus geometry changes with the redshift, this average viewing angle will also change. Thus, the ratio between the isotropic luminosity and observed luminosity may change systematically with redshift. Therefore, if we use quasars to measure the luminosity distance by evaluating the isotropic absolute luminosity and measuring the observed flux, we can have a redshift-dependent bias that can propagate to cosmological parameters. We propose a toy model for testing the effect of viewing angle uncertainty on the measurement of the luminosity distance. The model is based on analytical description of the obscuring torus applied to one-parameter observational data. It illustrates the possible change of the torus covering factor between the two chosen redshift ranges. We have estimated the possible errors in specific cosmological parameters (<jats:italic>H</jats:italic> <jats:sub>0</jats:sub>, Ω<jats:sub> <jats:italic>m</jats:italic> </jats:sub>) for the flat Lambda cold dark matter cosmology if a method is calibrated at low redshift and applied to the higher redshift. The errors in the cosmological parameters due to potential dependence of the viewing angle on redshift are found to be potentially significant, and the effect will have to be accommodated in the future in all quasar-based cosmological methods. A careful systematic study of AGNs means that a viewing angle across the redshift is necessary, with the use of appropriate samples and models that uniquely determine the inclination of each source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Sgr B1 is a luminous H <jats:sc>ii</jats:sc> region in the Galactic center immediately next to the massive star-forming giant molecular cloud Sgr B2 and apparently connected to it from their similar radial velocities. In 2018 we showed from SOFIA FIFI-LS observations of the [O <jats:sc>iii</jats:sc>] 52 and 88 <jats:italic>μ</jats:italic>m lines that there is no central exciting star cluster and that the ionizing stars must be widely spread throughout the region. Here we present SOFIA FIFI-LS observations of the [O <jats:sc>i</jats:sc>] 146 and [C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m lines formed in the surrounding photodissociation regions (PDRs). We find that these lines correlate neither with each other nor with the [O <jats:sc>iii</jats:sc>] lines although together they correlate better with the 70 <jats:italic>μ</jats:italic>m Herschel PACS images from Hi-GAL. We infer from this that Sgr B1 consists of a number of smaller H <jats:sc>ii</jats:sc> regions plus their associated PDRs, some seen face-on and the others seen more or less edge-on. We used the PDR Toolbox to estimate densities and the far-ultraviolet intensities exciting the PDRs. Using models computed with Cloudy, we demonstrate possible appearances of edge-on PDRs and show that the density difference between the PDR densities and the electron densities estimated from the [O <jats:sc>iii</jats:sc>] line ratios is incompatible with pressure equilibrium unless there is a substantial pressure contribution from either turbulence or magnetic field or both. We also conclude that the hot stars exciting Sgr B1 are widely spaced throughout the region at substantial distances from the gas with no evidence of current massive star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The detection of almost 100% linearly polarized emission from the fast radio burst source FRB 121102 implies coherent emission of relativistic electrons moving perpendicular to the ambient magnetic field. The origin of such a particle distribution is very intriguing. Given that FRB 121102 is likely driven by a neutron star, we explored orbits of charged particles trapped in a dipole magnetic field (the Störmer problem). Most previous studies focused on particles with relatively low energies so that the guiding center approximation may be applied. High-energy particles usually have chaotic orbits except those on a periodic orbit or near stable periodic orbits. Via evaluation of the maximum Lyapunov exponent of orbits of particles launched from the equatorial plane with an axial velocity (the angular velocity sets the length and energy scales of the system), we found prominent regions of quasi-periodic orbits around stable periodic orbits in the equatorial plane at high energies. Particles in these orbits oscillate around the equatorial plane and their radial distance from the dipole can vary by a factor of ∼2. Relativistic electrons in such orbits may be responsible for the almost 100% polarized emission from FRB 121102.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical follow-up observations for candidate clusters in the Clusters Hiding in Plain Sight survey, which is designed to find new galaxy clusters with extreme central galaxies that were misidentified as bright isolated sources in the ROSAT All-Sky Survey catalog. We identify 11 cluster candidates around X-ray, radio, and mid-IR-bright sources, including six well-known clusters, two false associations of foreground and background clusters, and three new candidates, which are observed further with Chandra. Of the three new candidates, we confirm two newly discovered galaxy clusters: CHIPS 1356-3421 and CHIPS 1911+4455. Both clusters are luminous enough to be detected in the ROSAT All-Sky Survey data if not because of their bright central cores. CHIPS 1911+4455 is similar in many ways to the Phoenix cluster, but with a highly disturbed X-ray morphology on large scales. We find the occurrence rate for clusters that would appear to be X-ray-bright point sources in the ROSAT All-Sky Survey (and any surveys with similar angular resolution) to be 2% ± 1%, and the occurrence rate of clusters with runaway cooling in their cores to be &lt;1%, consistent with predictions of chaotic cold accretion. With the number of new groups and clusters predicted to be found with eROSITA, the population of clusters that appear to be point sources (due to a central QSO or a dense cool core) could be around 2000. Finally, this survey demonstrates that the Phoenix cluster is likely the strongest cool core at <jats:italic>z</jats:italic> &lt; 0.7—anything more extreme would have been found in this survey.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We characterize in detail the two ∼0.3 pc long filamentary structures found within the subsonic region of Barnard 5. We use combined Robert C. Byrd Green Bank Telescope and Very Large Array observations of the molecular lines NH<jats:sub>3</jats:sub>(1,1) and (2,2) at a resolution of 1800 au, as well as James Clerk Maxwell Telescope continuum observations at 850 and 450 <jats:italic>μ</jats:italic>m at a resolution of 4400 and 3000 au, respectively. We find that both filaments are highly supercritical with a mean mass per unit length, <jats:italic>M</jats:italic>/<jats:italic>L</jats:italic>, of ∼80 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> pc<jats:sup>−1</jats:sup> after background subtraction, with local increases reaching values of ∼150 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> pc<jats:sup>−1</jats:sup>. This would require a magnetic field strength of ∼500 <jats:italic>μ</jats:italic>G to be stable against radial collapse. We extract equidistant cuts perpendicular to the spine of the filament and fit a modified Plummer profile as well as a Gaussian to each of the cuts. The filament widths (deconvolved FWHM) range between 6500 and 7000 au (∼0.03 pc) along the filaments. This equals ∼twice the radius of the flat inner region. We find an anticorrelation between the central density and this flattening radius, suggestive of contraction. Further, we also find a strong correlation between the power-law exponent at large radii and the flattening radius. We note that the measurements of these three parameters fall in a plane and derive their empirical relation. Our high-resolution observations provide direct constraints on the distribution of the dense gas within supercritical filaments showing pre- and protostellar activity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The <jats:italic>l</jats:italic> = +13 region in the Galactic center is characterized by multiple shell-like structures and their extremely broad velocity widths. We revisit the molecular superbubble hypothesis for this region, based on high-resolution maps of CO <jats:italic>J</jats:italic> = 1–0, <jats:sup>13</jats:sup>CO <jats:italic>J</jats:italic> = 1−0, H<jats:sup>13</jats:sup>CN <jats:italic>J</jats:italic> = 1−0, H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 1−0, SiO <jats:italic>J</jats:italic> = 2−1, and CS <jats:italic>J</jats:italic> = 2−1 lines obtained from the Nobeyama Radio Observatory 45 m telescope, as well as CO <jats:italic>J</jats:italic> = 3−2 maps obtained from the James Clerk Maxwell telescope. We identified 11 expanding shells with total kinetic energy and typical expansion time <jats:italic>E</jats:italic> <jats:sub>kin</jats:sub> ∼ 10<jats:sup>51.9</jats:sup> erg and <jats:italic>t</jats:italic> <jats:sub>exp</jats:sub> ∼ 10<jats:sup>4.9</jats:sup> yr, respectively. In addition, the <jats:italic>l</jats:italic> = +13 region exhibited high SiO <jats:italic>J</jats:italic> = 2−1/H<jats:sup>13</jats:sup>CN <jats:italic>J</jats:italic> = 1−0 and SiO <jats:italic>J</jats:italic> = 2−1/H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 1−0 intensity ratios, indicating that the region has experienced dissociative shocks in the past. These new findings confirm the molecular superbubble hypothesis for the <jats:italic>l</jats:italic> = +13 region. The nature of the embedded star cluster, which may have supplied 20–70 supernova explosions within 10<jats:sup>5</jats:sup> yr, is discussed. This work also shows the importance of compact broad-velocity-width features in searching for localized energy sources hidden behind severe interstellar extinction and stellar contamination.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stellar ultraviolet (UV) radiation drives photochemistry, and extreme-ultraviolet (EUV) radiation drives mass loss in exoplanet atmospheres. However, the UV flux is partly unobservable due to interstellar absorption, particularly in the EUV range (100–912 Å). It is therefore necessary to reconstruct the unobservable spectra in order to characterize the radiation environment of exoplanets. In the present work, we use a radiative transfer code <jats:monospace>SSRPM</jats:monospace> to build one-dimensional semiempirical models of two M dwarf exoplanet hosts, GJ 832 and GJ 581, and synthesize their spectra. <jats:monospace>SSRPM</jats:monospace> is equipped with an extensive atomic and molecular database and full-NLTE capabilities. We use observations in the visible, ultraviolet, and X-ray ranges to constrain atmospheric structures of the modeled stars. The synthesized integrated EUV fluxes are found to be in good agreement with other reconstruction techniques, but the spectral energy distributions disagree significantly across the EUV range. More than two-thirds of the EUV flux is formed above 10<jats:sup>5</jats:sup> K. We find that the far-ultraviolet (FUV) continuum contributes 42%–54% of the entire FUV flux between 1450 and 1700 Å. The comparison of stellar structures of GJ 832 and GJ 581 suggests that GJ 832 is a more magnetically active star, which is corroborated by other activity indicators.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The nature of GW190814's secondary component <jats:italic>m</jats:italic> <jats:sub>2</jats:sub> of mass 2.50–2.67 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> in the mass gap between the currently known maximum mass of neutron stars and the minimum mass of black holes is currently under hot debate. Among the many possibilities proposed in the literature, <jats:italic>m</jats:italic> <jats:sub>2</jats:sub> was suggested to be a superfast pulsar, while its <jats:italic>r</jats:italic>-mode stability against runaway gravitational radiation through the Chandrasekhar–Friedman–Schutz mechanism is still unknown. Previously, Fortin et al. constructed a sample of 33 unified equations of state using the same nuclear interactions from the crust to the core consistently; from that sample we use those equations that fulfill all currently known astrophysical and nuclear physics constraints to compare the minimum frequency required for <jats:italic>m</jats:italic> <jats:sub>2</jats:sub> to rotationally sustain a mass greater than 2.50 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> with the critical frequency above which the <jats:italic>r</jats:italic>-mode instability occurs. We use two extreme damping models assuming that the crust is either perfectly rigid or elastic. Using the stability of 19 observed low-mass X-ray binaries as an indication that the rigid crust damping of the <jats:italic>r</jats:italic>-mode dominates within the models studied, we find that <jats:italic>m</jats:italic> <jats:sub>2</jats:sub> is <jats:italic>r</jats:italic>-mode-stable while rotating with a frequency higher than 870.2 Hz (0.744 times its Kepler frequency of 1169.6 Hz) as long as its temperature is lower than about 3.9 × 10<jats:sup>7</jats:sup> K, further supporting the proposal that GW190814's secondary component is a supermassive and superfast pulsar.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Several publications highlight the importance of the observations of bow shocks to learn more about the surrounding interstellar medium and radiation field. We revisit the most prominent dusty and gaseous bow shock source, X7, close to the supermassive black hole, Sgr A*, using multiwavelength analysis. For the purpose of this study, we use Spectrograph for Integral Field Observations in the Near Infrared (SINFONI) (<jats:italic>H</jats:italic>+<jats:italic>K</jats:italic>-band) and NACO <jats:italic>L</jats:italic>′- and <jats:italic>M</jats:italic>′-band) data sets between 2002 and 2018 with additional COMIC/ADONIS+RASOIR (<jats:italic>L</jats:italic>′-band)<jats:xref ref-type="fn" rid="apjabd9c6fn1"> <jats:sup>7</jats:sup> </jats:xref> <jats:fn id="apjabd9c6fn1"> <jats:label> <jats:sup>7</jats:sup> </jats:label> <jats:p>COME-ON-PLUS Infrared Camera/Adaptive Optics Near Infrared System + Renouveau de l’Analyseur de Surface d’Onde InfraRouge</jats:p> </jats:fn> data of 1999. By analyzing the line maps of SINFONI, we identify a velocity of ∼200 km s<jats:sup>−1</jats:sup> from the tip to the tail. Furthermore, a combination of the multiwavelength data of NACO and SINFONI in the <jats:italic>H</jats:italic>-, <jats:italic>K</jats:italic>-, <jats:italic>L</jats:italic>′-, and <jats:italic>M</jats:italic>′-bands results in a two-component blackbody fit that implies that X7 is a dust-enshrouded stellar object. The observed ongoing elongation and orientation of X7 in the Br<jats:italic>γ</jats:italic> line maps and the NACO <jats:italic>L</jats:italic>′-band continuum indicate a wind arising at the position of Sgr A* or at the IRS16 complex. Observations after 2010 show that the dust and the gas shell seems to be decoupled in the projection from its stellar source S50. The data also implies that the tail of X7 thermally heats up due to the presence of S50. The gas emission at the tip is excited because of the related forward scattering (Mie scattering), which will continue to influence the shape of X7 in the near future. In addition, we find excited [Fe <jats:sc>iii</jats:sc>] lines, which together with the recently analyzed dusty sources and the Br<jats:italic>γ</jats:italic>-bar underline the uniqueness of this source.</jats:p>