| Description |
We propose HIFI observations of 1.9 THz (158 micron) CII line emission in selected 27 lines of sight (LOSs) which have been observed in H2 absorption in UV by FUSE, and three observed in CII 2325A absorption by STIS. CII observations provide a powerful probe of warm diffuse clouds, and CII is a useful as a tracer of their warm H2 content. By combining FUSE and STIS which directly detects H2 and C+ in absorption and the HIFI CII data we can better constrain many of the physical conditions in the cloud including the density and pressure of the C+ gas. The CII line emission spectra will be complimentary to those observed in absorption in UV and, in addition to its extremely high velocity resolution, help us resolve the narrow absorption features in the H2 and HI gas. A comparison of the molecular H2 column densities inferred from the 1.9THz CII line in the clouds along the FUSE/STIS LOS with those directly measured by them will validate the interpretation of the HIFI CII emission observed by larger scale Galactic surveys. We request 22.7 hrs of observing time on HIFI in band 7b. |
