| Abstract : | Neutral hydrogen 21 cm emission and absorption is an excellent tracer of the atomic interstellar medium and can be used to infer various physical properties of the gas in our galaxy. Recently, we have used 21 cm absorption and emission spectra from Galactic HI surveys to carry out a systematic comparison of properties between lines of sight through the gas disc in the Galactic plane and high Galactic latitude lines of sight through more diffuse gas. In this talk, I will present some of the interesting outcome from the VLA THOR survey data as well as an ongoing Galactic HI absorption survey using GMRT and WSRT. Based on our analysis, the gas in the plane has a sharp transition and flattening in the dust-gas correlation, likely related to the higher molecular gas fraction. On the other hand, the observed brightness temperature and optical depth correlation indicates some intrinsic difference in spin temperature distribution of the disk and the halo gas. This may be due to a small but non-negligible fraction of cold gas with slightly higher temperature and lower density present on the Galactic plane. In my talk I will discuss the broader implication of some of these results. |
