Trends in Triangulum: Evidence for Systematic Variations in the Nebular Content of M33's Massive Star-forming Regions
Abstract
Optical H-alpha and mid-infrared Spitzer/IRAC+MIPS mosaics of the Local Group Scd galaxy M33 are compared on both large and small scales. The H-alpha, 8-micron, and 24-micron images respectively trace the ionized, molecular (PAH), and granular (dust) phases associated with the galaxy's massive star-forming activity. The 8-micron emitting PAHs and 24-micron emitting dust are seen to fall off with galactocentric radius faster than the H-alpha emitting ionized gas. This galactocentric trend is confirmed by Spitzer/IRS spectroscopic scans of 8 HII regions that span a large range of galactocentric radius and corresponding metallicity. Such systematic behavior is likely due to an actual decrease in the abundance of PAHs and dust at large galactocentric radius. On smaller scales, the resolution-matched radial distributions of emission from individual HII regions show the 24-micron emitting dust to be the most compact component, and hence the best tracer of the clustered high-mass star formation. The HII regions NGC 604 and IC 133 show especially strong evidence for dust-embedded star formation.
We thank Frank Winkler for providing optical emission-line and red-continuum images of M33 as obtained with the Burrell-Schmidt telescope. W.H.W. acknowledges support through NASA/JPL under Spitzer GO program 3280. T.D.W. acknowledges support from NASA through a student fellowship from the Massachusetts Space Grant Consortium. This work comprises part of the Galactic Ecosystems Research and Mentorship (GERM) Initiative that is archived at http://go.tufts.edu/galacticecosystems.- Publication:
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American Astronomical Society Meeting Abstracts #213
- Pub Date:
- January 2009
- Bibcode:
- 2009AAS...21344304W