Molecular Gas and Star Formation in Atomic Gas Dominated Regions - Results from the HERACLES Survey

Details Molecular Gas and Star Formation in Atomic Gas Dominated Regions - Results from the HERACLES Survey Molecular Gas and Star Formation in Atomic Gas Dominated Regions - Results from the HERACLES Survey

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21934602s&link_type=abstract

American Astronomical Society, AAS Meeting #219, #346.02

Astronomy and Astrophysics

Astronomy

Scientific paper

We perform a sensitive search for faint CO emission and study how it is related to star formation in HI-dominated regions of 45 nearby spiral and dwarf galaxies using observations of CO (HERACLES), HI (THINGS), IR & Halpha (SINGS/LVL), and UV (GALEX NGS). Constraining the molecular gas content in HI-dominated regions is a crucial measurement to distinguish the role of atomic and molecular gas in the star formation process. We apply a novel technique, leveraging HI velocity fields from THINGS and wide area coverage of HERACLES to stack CO spectra and significantly increase the sensitivity. For spiral galaxies, CO (and thus H2) is linearly related to tracers of star formation (IR, Halpha, FUV) and does not depend on gas density. Meanwhile, the H2-to-HI ratio varies by several orders of magnitude with radius and total gas surface density and thus sensitively regulates the supply of star-forming molecular gas. For dwarf galaxies, we determine sensitive upper limits on the CO luminosity both near star-forming peaks and the entire galaxy and find CO emission to be faint both in an absolute sense and normalized by B-band luminosity and star formation rate (SFR). The ratio SFR/CO increases by more than an order of magnitude toward low metallicities which likely indicates a dramatic increase in the CO-to-H2 conversion factor.

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