X-ray absorption in Seyfert 2 galaxies

Abstract

We have studied the correlation among X-ray absorption, optical reddening and nuclear dust morphology in Seyfert 2 galaxies. Two main conclusions emerge: (i) the Balmer decrement and the amount of X-ray absorption are anticorrelated over a wide range of column density, 1021 ≲ NH ≲ 1024 cm-2 - the correlation no longer applies to Compton-thick objects (NH ≳ 1024 cm-2), although they span a comparable range in Balmer decrement; (ii) Compton-thin Seyfert 2s seem to prefer nuclear environments, which are rich in dust on scales of hundreds of parsecs. On the other hand, Compton-thick Seyferts indifferently exhibit 'dust-poor' and 'dust-rich' environments. These results support an extension of the Seyfert unification scenario (as recently proposed by Matt), where Compton-thick Seyfert 2s are observed through compact 'tori', whereas Compton-thin ones are obscured by dust on much larger scales.