The Dependence of the Star Formation Rate and the IMF on Environment: Insights from Spitzer and Herschel
Will Fischer, Rob Gutermuth, Erin Kryukova, Judy Pipher, Babar Ali, Mayra Osorio, Thomas Stanke, Amy Stutz and the HOPS team.
Surveys of nearby (400−800 pc) massive molecular clouds show that the surface density of young stellar objects varies by four orders of magnitudes, from dense crowded clusters forming both low- and high-mass stars to sparse environments forming isolated low mass stars. Of key importance is understanding the physical factors that control the density of young stars and their masses. We first overview Spitzer observations which indicate that, smoothed over 1 pc scales, the star formation rate per surface area scales as the gas column density squared (Gutermuth et al. submitted), and that the luminosity function of protostars is biased toward more luminous objects in crowded, cluster-forming, regions (hinting at a variable initial mass function − Kryukova et al. in prep). We then use data from the Herschel Orion Protostar Survey (HOPS) to examine in detail the crowded and clustered regions in the Orion molecular cloud. Using APEX LABOCA maps (850 micron) and HERSCHEL PACS images (160 micron) to map the structure of the dense gas on 0.03 pc scales, and using coordinated HST, Spitzer and Herschel 1.6−160 micron imaging and spectroscopy to constrain the properties and spatial distribution of protostars, we contrast the properties of the gas and protostars in rich clusters, small groups, and regions of isolated star formation.