Speaker
Simon Bihr
(Max Planck Institute for Astronomy)
Description
How do molecular clouds form from the diffuse atomic interstellar medium? To address this and further questions we are conducting the THOR survey, a galactic plane survey (l = 15 to 60dec and b = -1 to +1dec) of the 21cm HI line, four OH lines, and 20 recombination lines as well as the continuum from 1 to 2 GHz at a spatial resolution of ~20arcsec. We got granted 110 hours at the VLA in C-configuration. To test the configuration, we did a pilot study around the active star forming region W43 in 2012. The data analysis is work in progress and we combined our data with the VGPS survey (VLA Galactic plane survey - HI in D-configuration). This allows us to reconstruct all spatial scales down to 0.2-0.5pc. We will compare our data with CO data to study the cloud formation from the atomic to the molecular phase. We find significantly higher HI column densities for W43 than for other regions such as Perseus. The reason for these high column densities is under discussion, but we argue, that the strong interstellar radiation field of W43 prevents the formation of molecular hydrogen.
Author
Simon Bihr
(Max Planck Institute for Astronomy)