Molecular gas in the low-metallicity, star-forming dwarf IC 10

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 H I 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) M(.) of molecular gas using the Galactic CO-to-H(2) conversion factor. Observations with the ARO 12 m find that BIMA may resolve out as much as 50% of the CO emission, and we estimate the total CO luminosity as similar to 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-H(2) conversion factors, despite the low metallicity of IC 10 (Z approximate to 1/5 Z(.)). 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 H I. IC 10 displays a much higher star formation rate per unit molecular (H(2)) or total (H I+ H(2)) 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.