Sub-kpc scale gas density histograms of the nearby barred spiral galaxy M83: Multi-component molecular gas structure reflecting the galactic environment
We investigate the sub-kiloparsec (sub-kpc) molecular ISM structure and its relation to the galactic environment and star formation in the barred spiral galaxy M83 (NGC 5236). We employ the gas density histogram (GDH), which quantifies molecular gas surface density within $550~\mathrm{pc}\times550~\mathrm{pc}\times100~\mathrm{km~s^{-1}}$ cells. The GDHs are well described by one or two log-normal components, corresponding to the lower and higher-surface-density molecular components, referred to as L-LN and H-LN, respectively. The L-LN mass ($M_{\rm L}$) is relatively uniform across the disk, whereas the H-LN mass ($M_{\rm H}$) is highly structured and traces spiral arms. The fractional contribution of the H-LN component ($f^{\prime}_{\rm H}$) shows coherent structures across the disk and is enhanced along spiral arms, consistent with our previous Milky Way results. Moreover, while the L-LN correlates only weakly with star formation rate surface density ($Σ_{\rm SFR}$) and shows a steep Kennicutt-Schmidt (KS) relation with surface-density saturation reminiscent of atomic gas, the H-LN exhibits a tighter, nearly linear correlation similar to the conventional molecular KS relation. These results provide direct evidence that the molecular gas in M83 consists of multiple components. Star formation is more closely linked to the H-LN component, whereas the L-LN component appears to represent a more spatially extended molecular gas. Overall, our results suggest that galactic environments control the relative contribution of the two LN components, and that enhanced H-LN contribution is associated with elevated star formation activity.