Nobeyama Millimeter Array Observations of the Nuclear Starburst of M 83: A GMA Scale Correlation between Dense Gas Fraction and Star Formation Efficiency

We present aperture synthesis high-resolution (similar to 7 '' x 3 '') observations in CO (J = 1-0), HCN (J = 1-0), and 95 GHz Continuum emission toward the central (similar to 1.5 kpc) region of the nearby barred spiral galaxy M 83 with the Nobeyama Millimeter Array. Our high-resolution CO (J = 1-0) mosaic map depicts the presence of molecular ridges along the leading sides of the stellar bar and a nuclear twin peak structure, whereas the distributions of the HCN (J = 1-0) emission that traces dense molecular gas (n(H2) > a few x 10(4) cm(-3)) and the 95 GHz continuum emission that traces massive starburst show nuclear single-peak structures. The HCN (J = 1-0) and the 95 GHz continuum peaks are not spatially coincident with file optical starburst regions traced by the HST V-band image, suggesting the existence of deeply buried ongoing starburst due to strong extinction (A(V) similar to 5 map) near these peaks. We found that the HCN (J = 1-0)/CO (J = 1-0) intensity ratio, R-HCN/CO, correlates well with the extinction-corrected star formation efficiency (SFE) in the central region of M 83 at a resolution of 7.'' 5 (similar to 160 pc). This suggests that SFE is controlled by it dense gas fraction traced by R-HCN/CO, even on a Giant Molecular cloud Association (GMA) scale. Moreover, the correlation between R-HCN/CO and SFE in M 83 seems to be almost coincident with that among the Gao and Solomon (2004a, ApJ, 606, 271) sample. This Suggests that the correlation between R-HCN/CO and the SFE on a GMA (similar to 160pc) scale found in M 83 is the origin ofthe global correlation on a few kpc scale shown by Gao and Solomon (2004a).