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.
Publication
Internal structure of spiral arms traced with C II: Unraveling the warm ionized medium, H I, and molecular emission lanes | Velusamy T. et al. | Astronomy & Astrophysics Volume 578 id.A135 12 pp. | 578 | 10.1051\\/0004-6361\\/201525902 | 2015A&A...578A.135V | http://adsabs.harvard.edu/abs/2015A%26A...578A.135V
Thermal Pressure in Diffuse H2 Gas Measured by Herschel C II Emission and FUSE UV H2 Absorption | Velusamy T. et al. | The Astrophysical Journal Volume 838 Issue 2 article id. 165 15 pp. (2017). | 838 | 10.3847\\/1538-4357\\/aa5eaf | 2017ApJ...838..165V | http://adsabs.harvard.edu/abs/2017ApJ...838..165V
Instrument
HIFI_HifiPoint_load, HIFI_HifiMapping_load-raster
Temporal Coverage
2011-10-25T22:12:25Z/2012-09-28T12:01:25Z
Version
SPG v14.1.0
Mission Description
Herschel was launched on 14 May 2009! It is the fourth cornerstone mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
European Space Agency, velusamy et al., 2013, 'Structure of translucent clouds observed with HIFI SQUARE_BRACKET_OPENCIISQUARE_BRACKET_CLOSE 1.9THz and in H2 in absorption by FUSE', SPG v14.1.0, European Space Agency, https://doi.org/10.5270/esa-eo6uwwk
