[O III]γ5007, near-IR and X-ray properties of Seyfert 2 galaxies

Abstract

It is known that hard X-rays (2-10 keV) are a good indicator of the intrinsic luminosity of Seyfert 2 galaxies for those cases where they are transmitted through the torus, rather than seen purely by reflection, e.g., NGC 1068. It has recently been demonstrated that the [O III]γ5007 emission line and hard X-ray fluxes in Seyfert 2 galaxies follow the same correlation as found for Seyfert 1 galaxies, and hence that [O III]γ5007 emission line fluxes can also be used to infer the intrinsic power in AGNs. Recent theoretical models predict that the inner regions of the torus have hot dust with a blackbody peak around 3.5 μm (L band). We use comparisons of the hard X-ray, [O III]γ5007 and small-aperture L-band properties of low-redshift PG quasars, Seyfert 1 and 2 galaxies to infer the amount of reddening in the latter. The L band versus [O III]γ5007 and L band versus hard X-rays correlations found for unobscured objects (Seyfert 1 and PG quasars) allow us to estimate the torus-induced reddening in those obscured galaxies. Our values for the visual extinctions are compared with those values inferred from the hard X-ray column densities. In general we find a tendency for Seyfert 2 galaxies to have lower IR extinctions than those derived from the hard X-ray column densities, but they are nevertheless correlated in the sense that those Seyfert 2s with high column densities also display significant IR extinctions. Reddenings deduced using the small-aperture L-band data range from negligible AV up to 80 mag. © 1997 RAS.