Dust in the Emission-Line Gas of the Seyfert 2 Galaxy Markarian 3

Abstract

The results of photoionization models of the emission-line gas of the type 2 Seyfert galaxy Mrk 3 are presented. The models include cosmic dust with spectral properties similar to that found in the Galaxy. The effect of dust within the gas on the transfer of line radiation, particularly the UV resonance lines, and the contribution of the hot dust to the IR continuum of the galaxy are examined. The results of the models fit the observed properties of Mrk 3 closely enough to state, with reasonable certainty, that the observed emission lines arise in photoionized gas, and that the dust within the gas produces much of the observed IR continuum radiation. The model also predicts the existence of a small component of highly ionized, dense (nH about 10 to the 9.5/cu cm), dust-free gas within the nucleus of Mrk 3, from which UV resonance lines such as C IV (1549A) and Mg II (2800-A) arise. Such material must be within a fraction of parsec of the central source of Mrk 3. The existence of such a component implies that Mrk 3 possesses a small broad-line region.