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

摘要

We present the results of the wide-field ~(12)CO(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 45m telescope to recover the total flux. The target fields of the observations cover themolecular bar and part of the spiral arms, with a spatial resolution of ～110 pc × 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 semimajor radius of the bar. Within the observed field, HII regions brighter than 10~(37.6) erg s~(?1) in Hα 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 Hα and 24μm images. The arm-tointerarm ratio of the SFE is found to lie in the range of 2 to 5, while it is ～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.