[CII] DIFFUSE EMISSION OBSERVED BY IRTS

The [C II] 158 mu m line emission and the far-infrared continuum emiss ion at 155 mu m were observed by the Far-Infrared Line Mapper (FILM) a board the Infrared Telescope in Space (IRTS) with its high sensitivity and resolution. The observation was made along a great circle crossin g the galactic plane at l = 50 degrees and 230 degrees. Two components were found in their intensity distributions. The first component conc entrates on the galactic plane. It is prominent on the plane at l = 50 degrees, but is very faint at 230 degrees. The second component exten ds over at least 20 degrees in galactic latitude, and has nearly the s ame intensity at both crossing parts of the galactic plane. Therefore, the first one can be ascribed to emission from the galactic disk, and the second component to emission from the local interstellar gas. The intensity distribution of the [CII]] line of the second component is similar to that of the HI 21 cm integrated intensity. This fact sugges ts that the local [C II] emission component arises in the HI 21 cm lin e emitting gas. From the ratio of the [C II] line luminosity to the hy drogen column density, the interstellar cooling rate of the HI gas is (5.6 +/- 2.6) x 10(-27) erg s(-1) /H-atom, corresponding to the cold n eutral gas whose pressure is a few hundred cm(-3) K.