X-ray properties and evolution of high-redshift AGN, and the gas content of host galaxies

Vito, Fabio (2014) X-ray properties and evolution of high-redshift AGN, and the gas content of host galaxies, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Astronomia, 27 Ciclo. DOI 10.6092/unibo/amsdottorato/6729.
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In this thesis, I have investigated the evolution of the high-redshift (z > 3) AGN population by collecting data from some of the major Chandra and XMM-Newton surveys. The final sample (141 sources) is one of the largest selected at z> 3 in the X- rays and it is characterised by a very high redshift completeness (98%). I derived the spectral slopes and obscurations through a spectral anaysis and I assessed the high-z evolution by deriving the luminosity function and the number counts of the sample. The best representation of the AGN evolution is a pure density evolution (PDE) model: the AGN space density is found to decrease by a factor of 10 from z=3 to z=5. I also found that about 50% of AGN are obscured by large column densities (logNH > 23). By comparing these data with those in the Local Universe, I found a positive evolution of the obscured AGN fraction with redshift, especially for luminous (logLx > 44) AGN. I also studied the gas content of z < 1 AGN-hosting galaxies and compared it with that of inactive galaxies. For the first time, I applied to AGN a method to derive the gas mass previously used for inactive galaxies only. AGN are found to live preferentially in gas-rich galaxies. This result on the one hand can help us in understanding the AGN triggering mechanisms, on the other hand explains why AGN are preferentially hosted by star-forming galaxies.

Tipologia del documento
Tesi di dottorato
Vito, Fabio
Dottorato di ricerca
Scuola di dottorato
Scienze matematiche, fisiche ed astronomiche
Settore disciplinare
Settore concorsuale
Parole chiave
AGN, high-redshift, X-rays, surveys, gas, galaxies, evolution, obscuration
Data di discussione
12 Dicembre 2014

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