Is IRAS cirrus cloud emission largely fine-structure radiation?

Abstract

The contribution of line emission to the diffuse 'cirrus' radiation components observed by IRAS at 60 and 100 microns, respectively, is evaluated. The cirrus radiation was observed straddling the galactic plane to latitudes of + or - 80 degrees. Comparison of the observed brightness from cirrus clouds with forbidden line emission of O I and O III at 63 and 88 microns showed that the flux levels observed by IRAS are of the same order as the fine-structure line emission predicted by Stacey et al. (1985). It is argued that the fine-structure line emission from neutral gas at 63 microns as well as the line emission from diffuse ionized clouds at 88 microns, are significant components in most clouds, in some clouds they are the prime source of cirrus radiation.