Trey Wenger (University of Wisconsin-Madison)

Trey Wenger colloquium: Galactic HII regions, diffuse ionised gas, and structure in the Milky Way

Marsfield

Abstract

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 project, the Southern HII
Region Discovery Survey, and some preliminary results with the first
Galaxy-wide flux-limited HII region sample, including a novel
technique to constrain the Milky Way morphological structure. We
serendipitously discovered (1) a population of HII regions with
ionized gas velocity gradients and (2) RRL emission from diffuse
ionized gas. I will discuss these discoveries, their implications, and
our follow-up work, which will inform both models of high-mass star
formation as well as our understanding of the ISM and Galactic
structure.