A Molecular Star Formation Law in the Atomic Gas Dominated Regime in Nearby Galaxies

Understand

We use the IRAM HERACLES survey to study CO emission from 33 nearby spiral galaxies down to very low intensities.

• Using atomic hydrogen (HI) data, mostly from THINGS, we predict the local mean CO velocity from the mean HI velocity.
• By renormalizing the CO velocity axis so that zero corresponds to the local mean HI velocity we are able to stack spectra coherently over large regions as function of radius.
• This enables us to measure CO intensities with high significance as low as Ico = 0.3 K km/s (H2_SD = 1 Msun/pc2), an improvement of about one order of magnitude over previous studies.