  We revisit the proposed extended Schmidt law (Shi et al. 2011) which points
that the star formation efficiency in galaxies depends on the stellar mass
surface density, by investigating spatially-resolved star formation rates
(SFRs), gas masses and stellar masses of star formation regions in a vast range
of galactic environments, from the outer disks of dwarf galaxies to spiral
disks and to merging galaxies as well as individual molecular clouds in M33. We
find that these regions are distributed in a tight power-law as Sigma_SFR
~(Sigma_star^0.5 Sigma_gas )^1.09, which is also valid for the integrated
measurements of disk and merging galaxies at high-z. Interestingly, we show
that star formation regions in the outer disks of dwarf galaxies with Sigma_SFR
down to 10^(-5) Msun/yr/kpc^2, which are outliers of both Kennicutt-Schmidt and
Silk-Elmegreen law, also follow the extended Schmidt law. Other outliers in the
Kennicutt-Schmidt law, such as extremely-metal poor star-formation regions,
also show significantly reduced deviations from the extended Schmidt law. These
results suggest an important role for existing stars in helping to regulate
star formation through the effect of their gravity on the mid-plane pressure in
a wide range of galactic environments.
