Smith's Cloud: No chemistry but we did find some of the Milky Way's Missing Baryons

The Green Bank Observatory's 100 meter Green Bank Telescope (GBT) was used to search for OH emission from Smith's Cloud. Smith's Cloud is a large, few 10⁶ Solar Mass cloud which will impact the Milkay Way's disk in about 35 Million years. The origin of Smith's Cloud is uncertain but its environmental conditions should have allowed for the formation of molecules. The GBT OH observations did not detect any OH from Smith's Cloud and limits the metalicity to be below 3% solar. Sulpher has been observed in the Smith's Cloud with a metalicity of 0.5 solar. Since OH is the first molecule to form and should have been easily detected, the GBT observations indicate that there is currently no active chemistry occuring in Smith's Cloud.The observations did turn up a substantial amount of OH emission from the Milky Way along the line of sight. The observed lines of sight do not have any detected CO emission and suggests "dark gas" (dense enough to form OH but not CO) is present. The column density of this "dark gas" could be as high as 10^18-19 at a galactic latitude of 35^o. The "dark gas" could represent a significant fraction of the Milky Way's missing baryons.