X-ray, UV and FIR emission of Seyfert galaxies

Abstract

We have compiled multiwavelength data (in the radio, FIR, optical, UV and X-ray ranges) for a sample of 126 galaxies, including QSO, Seyfert 1, Seyfert 2 and galaxies dominated by star-forming processes. We have tested the implications of “unified Seyfert models”, which assume that Seyfert 1 and 2 galaxies are intrinsically the same kind of objects, but seen at different angles. A dense obscuring torus around the nuclcus would originate the spectral differences actually observed. From our data we conclude that the UV-soft X-ray emission can not be seen through the torus. On the other hand, the occultation/reflection picture underestimates significantly the UV luminosity.

We propose a scheme in which the intensity of the non-thermal nuclear engine decreases from QSO to Sy 2 galaxies, while the relative contribution of star-forming regions increases in the same direction. The relatively low soft X-ray emission in Sy 2 galaxies implies that their UV radiation should be dominated by starbursts, rather than by the nuclear engine.