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 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 × 106 K km s-1 pc2, equivalent to 4 × 106 M☉ of molecular gas using the Galactic CO-to-H2 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 ~2.2 × 106 K km s-1 pc2. 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 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 (H2) or total (H I+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.