The problem of extinction and thermal reradiation by dust in active galactic nuclei and quasi-stellar objects

Published H-alpha/H-beta ratios and infrared-to-visual flux ratios are examined as potential diagnostics for dust in Seyfert I galaxies, Seyfert 2 galaxies, and QSOs. H-alpha/H-beta ratio distributions are very broad although some subtle distinctions may be evident among the various classes of objects. The distributions of the ratio of about 10-micron luminosity to that at visual-ultraviolet wavelengths are more narrow, and clear distinctions are evident among the various types of object. Clearly both H-alpha/H-beta and infrared emission together help determine the obscuring effects of dust. More homogeneous data are desirable but will require considerably large telescope observing time in order to pursue these results further. 35 refs