Properties of the circumnuclear medium in Active Galactic Nuclei

We propose a classification scheme for the circumnuclear medium of AGNs based on their location in the A V −N H plane (related to dust absorption and gas absorption, respectively). We present evidence that the A V /N H ratio is often lower than the Galactic value. This is shown by the broad line ratios of a sample of intermediate Seyferts, and by the optical/X–ray ratio of line selected (as opposed to color selected) AGNs. We point out the implications for the physical properties of the absorber. A complete classification would require a third axis, related to the density of the absorber and/or its distance from the AGN.