Integrated star formation law revisited. I.

Using UV-based SFRs with individual IR-based dust corrections, we find that "normal" spiral galaxies alone define a tight {Sigma}_(HI+H2)-{Sigma}_SFR_ relation described by an n=1.41_-0.07_^+0.07^ power law with a dispersion of 0.28_-0.02_^+0.02^ (errors reflect fitting and statistical uncertainties).

The SFR surface densities are only weakly correlated with HI surface densities alone, exhibiting a stronger and roughly linear correlation with H_2_ surface densities, similar to what is seen in spatially resolved measurements of disks. However, many dwarf galaxies lie below the star formation law defined by spirals, suggesting a low-density threshold in the integrated star formation law. We consider alternative scaling laws that better describe both spirals and dwarfs.