Exploring (extremely) obscured accretion

Abstract

Most accretion in the Universe is thought to occur in obscured enviroments. Many different techniques are used to select obscured AGN. We present here the results of a selection of obscured AGN using their X-ray to optical flux ratio. Despite choosing a relatively high X-ray flux limit, most sources turn out to be only identifiable through 10 m-class spectroscopy. We have identified 22 sources (18 using GTC). Among the identified sources there are broad-line AGN (BLAGN), narrow emission line galaxies, and “normal galaxies”. 11 of those 17 turn out to be high-luminosity highly-absorbed AGN (the so-called QSO2). The two highest luminosity BLAGN are super-Eddington sources, while the third one appears to be a transition object between a type 2 and a type 1. This method appears to be quite efficient in selecting QSO2, but not more highly obscured sources, such as the long-sought Compton-Thick AGN.