Nobeyama millimeter array observations of the nuclear starburst of M 83: A GMA scale correlation between dense gas fraction and star formation efficiency

Abstract

We present aperture synthesis high-resolution (̃7" x 3") observations in CO (J = 1-0), HCN (./ = 1-0), and 95 GHz continuum emission toward the central (̃ 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 (/ = 1-0) emission that traces dense molecular gas (?H2 > a few x 104cm-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 the optical starburst regions traced by the HST V-band image, suggesting the existence of deeply buried ongoing starburst due to strong extinction (Ay ̃ 5 mag) near these peaks. We found that the HCN (/ = 1-0)/CO (J = 1-0) intensity ratio, /?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 (̃ 160 pc). This suggests that SFE is controlled by a dense gas fraction traced by Z?HCN/CO> even on a Giant Molecular cloud Association (GMA) scale. Moreover, the correlation between /?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 RHCN / CO and the SFE on a GMA (̃ 160pc) scale found in M 83 is the origin of the global correlation on a few kpc scale shown by Gao and Solomon (2004a). © 2009 Astronomical Society of Japan.