| Description |
The understanding of the processes governing the formation of interstellar clouds and subsequent star formation is key for our understanding of how galaxies evolve in our Universe. Special interest is given to the study of low-metallicity interstellar matter as it is thought to be representative of the environment where stars formed at earlier cosmological time. Unique targets for this study are the Large and Small Magellanic clouds, which are the closest low-metallicity star forming systems. We propose deep, velocity--resolved observations of the CII 158 um, CI 609um, and CI 370um lines towards 54 representative positions in the Large and Small Magellanic clouds with the HIFI instrument on board of Herschel. These will be combined with our MAGMA CO data to obtain a complete inventory of carbon in the Magellanic clouds. We selected positions to represent different ISM environments, based on whether they show: a) HI peaks with little or no 160um dust emission and no CO, b) HI and 160um peaks but still no CO, and c) CO peaks. We also include a sample of lines-of--sight observed by FUSE which have known H2 column densities, which will allow us to calibrate our use of CII as a tracer of HI and H2 column densities. Our sample therefore includes clouds in different stages of evolution going from diffuse atomic to diffuse molecular and to dense molecular clouds. We will use an excitation/radiative transfer code and a PDR model to derive the physical conditions of the line-emitting gas. Our observations have the potential to discover large quantities of dark H2 gas traced by CII and perhaps CI emission, as recently observed in CII emission in the galactic plane (Langer et al. 2010 and Velusamy et al. 2010). |
