On the nature of 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: a) the Balmer decrement and the amount of X-ray absorption are anticorrelated on a wide range of column density: 10^{21} < N_H < 10^{24} atoms/cm/cm. The correlation does no longer apply to Compton-thick objects (N_H < 10^{24} atoms/cm/cm), although they span a comparable range in Balmer decrement; b) Compton-thin Seyfert 2s seem to prefer nuclear environments, which are rich of dust on scales of the hundreds parsecs. On the other hand, Compton-thick Seyferts exhibit indifferently ``dust-poor&#39;&#39; and ``dust-rich&#39;&#39; environments. These results support an extension of the Seyfert unification scenario (as recently proposed by Matt, 2000), where Compton-thick Seyfert 2s are observed through compact ``torii&#39;&#39;, whereas Compton-thin ones are obscured by dust on much larger scales