Speaker
Tobias Röhser
(Universität Bonn)
Description
Intermediate-Velocity Clouds (IVCs) are HI clouds in the lower galactic halo that are thought to be related to a galactic fountain process. Most IVCs are predominantly atomic with a negligible fraction of molecular hydrogen (H_2) while molecular IVCs (MIVCs) are extremely rare. With respect to the galactic fountain hypothesis, IVCs and in particular MIVCs might be an important ingredient for the accretion of cold gas onto the Milky Way in order to sustain the ongoing star formation. For two particular IVCs, an atomic and a molecular cloud, we obtained high-resolution HI data with the Westerbork-Synthesis Radio Telescope and 12CO(1->0) and 13CO(1->0) emission maps with the IRAM 30m telescope. These observations allow us to study the important physical parameters to investigate the formation of molecular clouds at the disk-halo interface. We find that the differences in the small-scale structure of the atomic and molecular IVCs reflect their different chemical state. By comparing the measured 12CO(1->0) emission to the inferred H_2 distribution, extracted from the FIR data of the Planck satellite, we find strong variations of the X_CO factor with low conversion factors at the CO emission peaks. We discuss the prerequisites for the formation of MIVCs by analysing the conditions in other high-latitude atomic and molecular clouds.
Author
Tobias Röhser
(Universität Bonn)