|
Radio recombination lines (RRLs) are an unobscured tracer of ionized gas in both the diffuse interstellar medium (ISM) as well as high-mass star forming regions. The HII Region Discovery Surveys (HRDS) have nearly tripled the number of known high-mass star forming regions in the Milky Way by detecting RRL emission toward infrared-identified HII region candidates. HII regions are the classic tracer of structure in galaxies, and their physical conditions (e.g., metallicity, internal kinematics) inform models of high-mass star formation and Galactic chemodynamical evolution. I will give a brief overview of our latest Australia Telescope Compact Array HRDS project, the Southern HII Region Discovery Survey, highlight two serendipitous RRL discoveries and their implications, and preview some preliminary results with the first Galaxy-wide flux-limited HII region sample. In particular, I will describe two novel techniques -- enabled by our now-complete HII region sample -- to constrain the morphological structure of the Milky Way disk. |
|