Emission-Line Probes of Circumnuclear Dust in AGNs

Abstract

Emission lines that trace elements subject to strong depletion onto grains provide a means for probing the dust content of AGNs. Examples include infrared [FeII] and optical [CaII] lines. The excitation mechanisms underlying the [FeII] lines remain controversial, resulting in related disagreement over the gas-phase abundance of iron in Seyfert narrow-line regions. In this contribution we emphasize the utility of the [CaII] lines as a consistency test for claims of grain destruction affecting the [FeII] lines. A search for [CaII] emission in NGC 1068 at a location of strongest [FeII] emission along the radio jet yields a strong upper limit, but no detection. This result suggests that grains survive largely intact in a region that otherwise shows strong evidence of shock processing.

6 pages (LaTeX, paspconf.sty), 1 postscript figure, to appear in proceedings of "Structure and Kinematics of Quasar Broad Line Regions" (1998 March 23-26, Lincoln, Nebraska), eds. C.M. Gaskell et al