Cool gas and dust in M 33: Results from the HERschel M 33 Extended Survey (HERM33ES)
Boquien, M.; Braine, J.; Calzetti, D.; van der Werf, P.; Bertoldi, F.; Combes, F.; Aalto, S.; Henkel, C.; Israel, F.; Kramer, C.; Relaño, M.; Verley, S.; Xilouris, E. M.; Buchbender, C.; Gratier, P.; Schuster, K. F.; Mookerjea, B.; van der Tak, F.; Rosolowsky, E.; Quintana-Lacaci, G.; Garcia-Burillo, S.; Gonzalez, M.; Koribalski, B.; Tabatabaei, F.; Wiedner, M.; Roellig, M.
France, Spain, Greece, Canada, United States, Germany, Netherlands, Sweden, Australia, India, United Kingdom
Abstract
We present an analysis of the first space-based far-IR-submm observations of M 33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M 33 is a first step towards young low-metallicity galaxies where the submm may be able to provide an alternative to CO mapping to measure their H2 content. In this Letter, we measure the dust emission cross-section σ using SPIRE and recent CO and H i observations; a variation in σ is present from a near-solar neighborhood cross-section to about half-solar with the maximum being south of the nucleus. Calculating the total H column density from the measured dust temperature and cross-section, and then subtracting the H i column, yields a morphology similar to that observed in CO. The H2/H i mass ratio decreases from about unity to well below 10% and is about 15% averaged over the optical disk. The single most important observation to reduce the potentially large systematic errors is to complete the CO mapping of M 33.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.