2004ApJ...602..723H

The relationship between the star formation rate and surface density of neutral gas within the disk of M33 is examined with new imaging observations of ¹²CO J=1-0 emission gathered with the Five College Radio Astronomy Observatory (FCRAO) 14 m telescope and IRAS HiRes images of the 60 and 100 µm emission. The Schmidt law, Σ_SFR~Σⁿ_gas, is constructed using radial profiles of the H I 21 cm, CO, and far-infrared emission. We identify a strong correlation between the star formation rate and molecular gas surface density. This suggests that the condensation of giant molecular clouds (GMCs) is the limiting step to star formation within the M33 disk. The corresponding molecular Schmidt index, n_mol, is 1.36±0.08. The star formation rate has a steep dependence on total mass gas surface density, (Σ_HI_+ΣH₂_), owing to the shallow radial profile of the atomic gas that dominates the total gas surface density for most radii. The disk pressure of the gas is shown to play a prominent role in regulating the molecular gas fraction in M33.