Speaker
Description
Most AGN studies find that the obscured AGN fraction decreases as the luminosity increases. This is usually explained by invoking receding torus models. However, recent results for the intrinsic type 2 fraction based on a complete hard X-ray selected sample (BUXS: Bright Ultrahard XMM-Newton Survey) showed little to no luminosity dependence, and uncovered a population of hidden luminous Compton-thick AGN. We furthered this analysis by applying a fully Bayesian approach to derive the distribution of column densities ($N_H$) for the 252 AGN with spectroscopic redshifts within BUXS. For a sub-sample of type 1 AGN at $z=0.05-1$, we compared these results to the ones obtained for the optical obscuration. We fitted the optical spectra to classify the sources in types (1.0-1.9), based on emission line ratios, and to measure the optical-UV continuum obscuration ($A_V$). We find that there is a clear tendency towards increasing $A_V$ and $N_H$ from 1.0 to 1.9 objects, with a statistically significant difference between the 1.0-1.2-1.5 and 1.8-1.9 subsets, showing that they are different families. Regarding the dust-to-gas ratio ($A_V$ vs. $N_H$) we do not find a clear tendency, instead the distribution shows a large scatter. We have also explored the suitability of the ratio of the broad H$\alpha$ and H$\beta$ emission lines to estimate the obscuration in type 1 AGN, finding average values similar to previous ones but with substantial dispersion, concluding that this ratio should be taken with extreme caution, if not discarded as an obscuration measurement altogether.
| Affiliation | IFCA (CSIC-UC, Spain) |
|---|---|
| Topic | Active Galactic Nuclei: accretion physics and evolution across cosmic time |
