Warm and Cold Molecular Gas in Galaxies

New and archival interferometric 12CO(1->0) datasets from six nearby galaxiesare combined with H_2 2.122um and H-alpha maps to explore in detail theinterstellar medium in different star-forming galaxies. We investigate therelation between warm (H_2 at T~2000 K) and cold (CO at T~50 K) molecular gasfrom 100 pc to 2 kpc scales. On these scales, the ratio of warm-to-coldmolecular hydrogen correlates with the fnu(60um)/fnu(100um) ratio, a ratio thattracks the star formation activity level. This result also holds for the globalproperties of galaxies from a much larger sample drawn from the literature. Thetrend persists for over three orders of magnitude in the mass ratio, regardlessof source nuclear activity.Comment: 13 pages including 4 figures; accepted for publication in the Astronomical Journa