Distribution and kinematics of molecular gas in barred spiral galaxies. II. NGC 253

The large scale mapping of the disk of a nearby barred galaxy, NGC 253 in CO (J = 1-0), was made with an angular resolution of 16". Molecular gas concentrates in the nuclear region and the large-scale bar seen in near-infrared images. The radial distribution of molecular gas indicates a secondary peak, whose radius agrees with that of the H alpha ring and the ends of the bar, as well as a central strong peak. The radial distribution is well fitted by an exponential function or a power law outside the secondary peak. A rotation curve is rising in the inner region and changes to flat at the ring. These facts suggest that molecular gas infalls from the outer disk by losing angular momentum due to gaseous viscosity in the region of the differential rotation, and accumulates at the ring. In the bar region land within the corotation radius), molecular gas again loses its angular momentum due to the bar potential, and is infalling toward the nuclear region. The upper limit of the noncircular motion along the major axis of the bar in the leading edge of the bar is approximate to 70-130 km s(-1) in the rest frame of the bar.