Kennicutt-Schmidt relation variety and star-forming cloud fraction
  The observationally derived Kennicutt-Schmidt (KS) relation slopes differ
from study to study, ranging from sub-linear to super-linear. We investigate
the KS-relation variety (slope and normalization) as a function of integrated
intensity ratio, R31=CO(J=3-2)/CO(J=1-0) using spatially resolved CO(J=1-0),
CO(J=3-2), HI, Ha and 24um data of three nearby spiral galaxies (NGC3627,
NGC5055 and M83). We find that (1) the slopes for each subsample with a fixed
R31 are shallower but the slope for all datasets combined becomes steeper, (2)
normalizations for high R31 subsamples tend to be high, (3) R31 correlates with
star-formation efficiency, thus the KS relation depends on the distribution in
R31-Sigma_gas space of the samples: no Sigma_gas dependence of R31 results in a
linear slope of the KS relation whereas a positive correlation between
Sigma_gas and R31 results in a super-linear slope of the KS relation, and (4)
R31-Sigma_gas distributions are different from galaxy to galaxy and within a
galaxy: galaxies with prominent galactic structure tend to have large R31 and
Sigma_gas. Our results suggest that the formation efficiency of star-forming
cloud from molecular gas is different among galaxies as well as within a galaxy
and is one of the key factors inducing the variety in galactic KS relation.
