The infrared luminosity of the torus and the visibility of scattered broad line emission in Seyfert 2 galaxies

Abstract

A number of studies have shown that the visibility of scattered broad emission lines in Seyfert 2 galaxies is strongly dependent on the IRAS f_60/f_25 flux ratio, where those Seyfert 2s with `warm' IRAS colours show polarised broad line emission. It is now clear that this effect is due to the increasing dominance of the galactic rather than the AGN emission at 60um in less luminous `cool' Seyfert 2s. However, we present evidence that the 25um emission is a good measure of the AGN luminosity for most Seyfert 2s. Using this result, we show that the visibility of scattered broad line emission has a dependence on the AGN luminosity. The observations can be interpreted self-consistently if the scale height of the scattering zone varies with central source luminosity whilst the scale height of the obscuring torus is approximately constant.