Environmental Dependence of Star Formation Law in the Disk and Center of
  IC 342
  The Kennicutt-Schmidt (K--S) law in IC 342 is examined using the 12CO-to-H2
conversion factor (Xco,v), which depends on the metallicity and CO intensity.
Additionally, an optically thin 13CO (1-0) is also independently used to
analyze the K--S law. Xco,v is two to three times lower than the Galactic
standard Xco in the galactic center and approximately two times higher than Xco
at the disk. The surface densities of molecular gas (Sigma_H2) derived from
12CO and 13CO are consistent at the environment in a high-Sigma_H2 region. By
comparing the K-S law in the disk and the central regions of IC 342, we found
that the power law index of K-S law (N) increases toward the central region.
Furthermore, the dependence of N on Sigma_H2 is observed. Specifically, N
increases with Sigma_H2. The derived N in this work and previous observations
are consistent with the implication that star formation is likely triggered by
gravitational instability in the disk (low-Sigma_H2 region) of IC 342 and both
gravitational instability and cloud-cloud collisions in the central region
(high-Sigma_H2 regime). In addition, the increasing N toward the high-Sigma_H2
domain also matches the theoretical prediction regarding the properties of
giant molecular clouds. The results of IC 342 are supported by the same
analysis of other nearby galaxies.
