The Metallicity Dependence of the CO-to-H[TINF]2[/TINF] Conversion Factor from Observations of Local Group Galaxies

Abstract

High-resolution CO maps of 9 molecular clouds in IC 10 are combined with the\nnew measurement of the distance to this nearby metal poor galaxy to measure\naccurately the CO-to-H2 conversion factor. The result for IC 10 is combined\nwith published data for four other Local Group galaxies (M31, M33, NGC 6822,\nthe SMC) to trace the dependence of the CO-to-H2 conversion factor on oxygen\nabundance. These data show conclusively that the CO-to-H$_2$ conversion factor\nincreases as the metallicity of the host galaxy decreases, with the conversion\nfactor increasing by a factor of 4.6 for a factor of 10 decrease in\nmetallicity.\n