Environmental dependence of star formation law in the disk and center of IC 342

Abstract

Abstract 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 ($\Sigma_{\mathrm{H_{2}}}$) derived from 12CO and 13CO are consistent with the environment in a high-$\Sigma _{\mathrm{H_{2}}}$ 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 the K–S law (N) increases toward the central region. Furthermore, the dependence of N on $\Sigma _{\mathrm{H_{2}}}$ is observed. Specifically, N increases with $\Sigma _{\mathrm{H_{2}}}$. 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-$\Sigma _{\mathrm{H_{2}}}$ region) of IC 342 and both gravitational instability and cloud–cloud collisions in the central region (high-$\Sigma _{\mathrm{H_{2}}}$ regime). In addition, the increasing N toward the high-$\Sigma _{\mathrm{H_{2}}}$ 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.