Tesis postgrado Astrofísica

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Examinando Tesis postgrado Astrofísica por Autor "Arévalo, Patricia"

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  • Miniatura
    Ítem
    Demystifying the powering mechanism of low-luminosity active galactic nuclei
    (Universidad de Valparaíso, 2022-08) Díaz Ramírez, Yaherlyn; Arévalo, Patricia; Hernández-García, Lorena
    Despite the long history of studies of active galactic nuclei (AGN), details on the structure of the accretion mechanism are far from clear. The work presented in this thesis is directed at unveiling properties of the structures in AGN through broad- band X-ray spectroscopy, with particular emphasis on broad X-ray band using XMM- Newton+NuSTAR+Swift (0.5–110.0 keV) data. With its unprecedented spectral sensi- tivity in this energy band, the combination of these telescopes provides the key obser- vational diagnostics of the properties of the AGN X-ray source, the corona, and the surrounding gas in the accretion disk and the torus. In this thesis we focused on the study of of Low-luminosity AGN (LLAGN), aiming at disentangle their inner structure, with emphasis on the reflection and the accretion mechanism. The first part of the document is centered on the develop- ment of the methodology and its application to one particular LLAGN, NGC 3718 (L/LEdd ∼ 10−5). Developing a methodology to study properties of potential reflec- tors and explore the improvement in the spectral index estimation considering high energy data and torus or disk like reflection models. We found that the inclusion of these models and high energy data allows to place strong constraints on the geometry and physical features of the surroundings as well to obtain more restricted values of a torus and a disk reflector. Then we applied this methodology to a sample of 17 LLAGN from BASS/DR2 combining observations from XMM-Newton, NuSTAR and Swift and applying the same methodology that was previously developed in the first work in NGC 3718. From the analysis of the X-ray data of the AGN sample, we found a relation which is indicative of a change in the column density of the torus like reflector at lower ac- cretion rates. Also, we confirm an anti-correlation between Γ-Eddington ratio with smaller scatter than previously reported, thanks to the inclusion of high energy data and the reflection models. The change in the correlation Γ-λEdd at ∼10−3 that we found is in agreement with a different accretion mechanism compared with higher accretion AGN as was previously reported in the literature.
  • Miniatura
    Ítem
    The growth of supremassive black holes in galaxies: co-evolution and rgulation of the star formation activity
    (Universidad de Valparaíso, 2021) Carraro Apablaza, Rosamaría; Arévalo, Patricia
    In this Thesis we study how the accretion of the central supermassive black hole evolves in galaxies in all their star formation life phases and through a wide range of cosmic epochs. We take two complementary approaches. First, we perform a statistical study on a large sample of galaxies from the COSMOS field where we take advantage of X- ray Chandra data to estimate black hole accretions, via a combination of stacked data and individual detections, and compare them with their star formation properties, estimated from far-infrared emission combined with ultra-violet emission. Then, we use semi-empirical models to create galaxy mock catalogs onto which we perform an analogous analysis in order to pin down which parameters control the black holes’ X-ray emission and its evolution. We find a picture in which the bulk of the black hole and stellar masses are accreted in the star forming phase through secular processes, where the average black hole ac- cretion follows a relation with stellar mass similar to the “main sequence”, i.e. the relation between the star formation rate and the stellar mass followed by star forming galaxies, having a similar evolution in time but with a more efficient accretion at high stellar masses. The starburst phase appears to have a significant enhancement of the SFR but a lesser impact on the black hole accretion, which has a samller enhancement especially at high redshift. Quiescent galaxies, on the other hand, undergo a signifi- cant decline in their star formation, while the black hole accretion is still noticeable. This observed evolution of the X-ray luminosity with time and galaxy phase is com- patible with a change in the average Eddington ratio but is mostly independent on the duty cycle. We find a super-linear relation between black hole and stellar mass which, in order to reproduce the observations, should be combined with an average Eddington ratio that depends on stellar mass. Our results point in the direction of galaxy downsizing, i.e. a fast accretion of the black hole and stellar mass at very high redshift for the most massive galaxies, followed by a steep decrease in accretion, while low-mass galaxies accrete their mass more slowly, with an accretion rate that decreases more slowly with time. On a separate note, we study the gas distribution in a sample of local active galax- ies, by analyzing their continuum and reflected X-ray light curves and reproducing the observed damping of the variations of the reflected component through Monte Carlo simulations.