Molecular Gas in the Low Metallicity, Star Forming Dwarf IC 10

Abstract

We present a complete survey of CO 1->0 emission in the Local Group dwarf irregular IC 10. The survey, conducted with the BIMA interferometer, covers the stellar disk and a large fraction of the extended HI envelope with the sensitivity and resolution necessary to detect individual giant molecular clouds (GMCs) at the distance of IC 10 (950 kpc). We find 16 clouds with a total CO luminosity of 1 x 10^6 K km s^-1 pc^2, equivalent to 4 x 10^6 Msun of molecular gas using the Galactic CO-to-H2 conversion factor. Observations with the ARO 12m find that BIMA may resolve out as much as 50% of the CO emission, and we estimate the total CO luminosity as 2.2 x 10^6 K km s^-1 pc^2. We measure the properties of 14 GMCs from high resolution OVRO data. These clouds are very similar to Galactic GMCs in their sizes, line widths, luminosities, and CO-to-H2 conversion factors despite the low metallicity of IC 10 (Z ~ 1/5 Zsun). Comparing the BIMA survey to the atomic gas and stellar content of IC 10 we find that most of the CO emission is coincident with high surface density HI. IC 10 displays a much higher star formation rate per unit molecular (H2) or total (HI+H2) gas than most galaxies. This could be a real difference or may be an evolutionary effect - the star formation rate may have been higher in the recent past.