Nature 319, 646 - 647 (20 February 1986); doi:10.1038/319646a0

Is IRAS cirrus cloud emission largely fine-structure radiation?

Martin Harwit, James R. Houck & Gordon J. Stacey^*

Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853, USA
^*Present address: Physics Department, University of California, Berkeley, California 94720, USA.

One of the more interesting observations made by the infrared astronomical satellite (IRAS) mission is the discovery of a diffuse 'cirrus' component seen at 60 and 100 µm (bands 3 and 4). It straddles the galactic plane and extends, in patches, to latitudes of 80° (refs 1, 2). Comparison of the observed brightness from these clouds with [O I] 63-µm and [O III] 88-µm fine-structure line emission, calculated on the basis of observed [C II] emission from the galactic plane, shows the flux levels observed by IRAS to be of the same order as the expected fine-structure line emission³. We propose here that fine-structure line emission, from neutral gas at 63 µm and from diffuse ionized clouds at 88 µm, is a significant component and in some clouds perhaps the prime source of the cirrus radiation.

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