EPoS Contribution
EPoS Contribution
Is there an energy threshold for triggered star formation?

Michael Alexander
University of Wyoming, Laramie, WY, USA
Feedback from massive stars has the potential to trigger a new generation of star formation. We report initial results from an investigation into triggered star formation on the periphery of infrared-bright Galactic bubbles powered by a range of energies, from those harboring many massive stars to those at the cusp of forming massive stars. We use a combination of infrared photometry from 2MASS, UKIDSS, and Spitzer GLIMPSE to build SEDs, classify young stellar objects within each region, and search for a spatial age gradient suggestive of a wave of star formation moving radially outward with the bubble. We also describe in detail the molecular cloud environment using data from the 13-CO Galactic Ring Survey and new data from the Herschel Hi-GAL survey. We employ these datasets on our test region, G38.91-0.42, an intermediate- to high-mass star forming complex at a distance of 2.7 kpc. We find evidence for two small, compact star clusters, each driving an expanding bubble. We identify and classify 159 YSOs, most of which lie in regions of high gas surface density. Using the Herschel 500 micron data, we find a clear correlation between YSO surface number density and gas surface density, similar to that of Gutermuth et al. 2011. Curiously, the correlation between gas surface density and the mass of an individual YSO is much weaker. We find only marginal evidence for triggering; however, the largest bubble has an age of just 0.5 Myr, which may not allow enough time to collect and compress interstellar material to form new stars. The results from this region will be combined with studies of other, more energetic bubbles in order to assess the efficiency of triggering among regions with a range of mechanical and ionizing luminosities.
Henry Kobulnicky, U of Wyoming, USA
Charles Kerton, Iowa State, USA