Dust-sensitive forbidden line ratios

The paper studies observations of certain pairs of forbidden emission lines in the redshifted spectra of intrinsically bright objects, which may make possible the study of dust at large distances. The forbidden line pairs most likely to be useful in detecting dust in both galactic and extragalactic objects are presented, and forbidden O III 2322, 4364 A, which is the best line pair for the ground-based detection of dust intermediate-redshift quasars is discussed. Spectrophotometric observations at 1-2 microns could permit the study of dust toward highly luminous quasars at redshifts as large as 5, and quasars brighter than visual magnitude 17 are presented as candidates for studying dust with forbidden O III 2322, 4364 A.