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This Week at Physics

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Event Number 5075

  Thursday, April 4th, 2019

Astronomy Colloquium
"Science with a Complete Catalog of Galactic HII Regions"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Speaker: Loren Anderson, West Virginia University
Abstract: HII regions are the signature of ongoing high-mass star formation, and are key to understanding star formation and feedback. Modern mid-infrared surveys have for the first time enabled a complete census of Galactic HII regions, and with such a census we can get a global view of high-mass star formation in the Milky Way. We found that all HII regions have the same mid-infrared morphology of ~20um emission surrounded by ~10um emission. The former is largely due to small grains scholastically heated in the HII region plasma and the latter is mostly caused by emission from polycyclic aromatic hydrocarbons. We used mid-infrared survey data to create a catalog of all objects sharing this morphology in the Galaxy, the "WISE Catalog of Galactic HII Regions." This catalog has over 8000 entries, ~2000 of which are known to be HII regions, ~2000 of which are HII region candidates with radio continuum emission from ionized gas, and ~4000 of which are radio-quiet candidates. Radio recombination line observations can turn HII region candidates into known regions, and radio continuum observations can turn radio quiet candidates into candidates. I will detail our efforts on these two fronts, which together have allowed us to determine the Galactic locations of a large number of HII regions and to estimate the overall HII region population.

Over large portions of the Milky Way, the WISE catalog is now statistically complete for all HII regions ionized by single O-stars. With such a catalog, we can begin to examine the overall Galactic HII region population, and to compare massive star formation in the Milky Way with that of external galaxies. Our current investigations include the z-distribution of massive star formation regions and the Sun's height above the midplane, the form Galactic HII region luminosity function, massive star formation in the far outer Galaxy, the Galactic electron temperature gradient, a strange cluster of HII regions near to the Galactic center, the distribution of ionized gas in the inner Galaxy, and the luminosity and star formation rate of the Milky Way.
Host: Robert Benjamin
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