Astronomy Colloquium

Wednesday, March 20, 2019

4:00pm to 5:00pm

Cahill, Hameetman Auditorium

The Balance of Power in Galactic Massive Star-Forming Regions

Matthew Povich, Cal Poly Pomona,

The star formation rate (SFR) is a fundamental parameter in theoretical models of galaxy evolution and governs the observed properties of galaxies. The most widely-used empirical measurements of the SFR in both the Milky Way and external galaxies rely on indirect observational tracers sensitive to only the most massive 1% of stars. Hence state-of-the-art astrophysical methods for diagnosing galactic star-formation activity are analogous to using only the tax returns and investment portfolios of the richest 1% of earners to diagnose U.S. economic activity.I will present recent work to model the 3.6 micron through 10 mm spectral energy distributions (SEDs) for a sample of 28 young Galactic massive star-forming regions. We performed large-aperture photometry on archival imaging data obtained using an armada of space-based observatories: Spitzer, MSX, IRAS, Herschel, and Planck and fit the resulting SEDs with multi-component dust, black-body, and power-law continuum models. Because the massive stellar content in the majority of these regions has been spectroscopically cataloged, we balance the "energy budgets" in each region by comparing the luminosity input by stars to that emerging in the SEDs. We find that ∼34% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ∼68% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photo dissociation regions. We calibrate infrared and radio diagnostics of obscured SFRs to the known ionizing stellar populations. Widely-employed extragalactic SFR calibrations based on 24 micron luminosity agree with our calibrations to within 30%, while analogous extragalactic calibrations based on 70 micron luminosity must be corrected for the smaller physical size of individual Galactic regions.I will also discuss plans to map the SFR distribution in our home Galaxy by applying our new SFR calibrations to 2600 Galactic star-forming regions cataloged by Zooniverse citizen scientists for the Milky Way Project (www.milkywayproject.org).

For more information, please contact Judy McClain by phone at 626-395-4970 or by email at [email protected].

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