Warm and Cold Molecular Gas in Galaxies
  New and archival interferometric 12CO(1->0) datasets from six nearby galaxies are combined with H_2 2.122um and H-alpha maps to explore in detail the interstellar medium in different star-forming galaxies. We investigate the relation between warm (H_2 at T~2000 K) and cold (CO at T~50 K) molecular gas from 100 pc to 2 kpc scales. On these scales, the ratio of warm-to-cold molecular hydrogen correlates with the fnu(60um)/fnu(100um) ratio, a ratio that tracks the star formation activity level. This result also holds for the global properties of galaxies from a much larger sample drawn from the literature. The trend persists for over three orders of magnitude in the mass ratio, regardless of source nuclear activity. 
Daniel A. Dale (1), Kartik Sheth (2), George Helou (2,3), Michael W.   Regan (4), Susanne Huttemeister (5) ((1) U. Wyoming, ...