Wide-field 12CO (J=1-0) imaging of the nearby barred galaxy M 83 with NMA and Nobeyema 45 m telescope: Molecular gas kinematics and star formation along the bar

We present the results of the wide-field (CO)-C-12(1-0) observations of the nearby barred galaxy M 83 carried out with the Nobeyama Millimeter Array (NMA). The interferometric data are combined with the data obtained with the Nobeyama 45 m telescope to recover the total flux. The target fields of the observations cover the molecular bar and part of the spiral arms, with a spatial resolution of similar to 110 pc x 260 pc. By exploiting the resolution and sensitivity to extended CO emission, the impact of the galactic structures on the molecular gas content is investigated in terms of the gas kinematics and the star formation. By inspecting the gas kinematics, the pattern speed of the bar is estimated to be 57.4 +/- 2.8 km s(-1) kpc(-1), which places the corotation radius at about 1.7 times the semi-major radius of the bar. Within the observed field, H II regions brighter than 10(37.6) erg s (1) in H alpha luminosity are found to be preferentially located downstream of the CO-emitting regions. Azimuthal angular offsets between molecular gas and star forming (SF) calculated with the angular cross-correlation method confirm the trend. By comparing with a cloud orbit model based on the derived pattern speed, the angular offsets are found to be in accordance with a time delay of about 10 Myr. Finally, to test whether the arm/bar promote star formation efficiency [SFE = Star Formation Rate (SFR)/H-2 mass], SFR is derived with the diffuse-background-subtracted H alpha and 24 mu m images. The arm-to-interarm ratio of the SFE is found to lie in the range of 2 to 5, while it is similar to 1 if no background removal is performed. The CO-SF offsets and the enhancement of the SFE in the arm/bar found in the inner region of M 83 are in agreement with the predictions of the classical galactic shock model.