CO in the barred galaxy NGC 1530

We present observations of the barred spiral NGC 1530 in CO (1-0) with the IRAM Interferometer and in CO (1-0) and (2-1) with the IRAM 30 m telescope. Along the bar there is abundant molecular gas associated with the dust lanes seen on optical images. Near the nucleus, the interferometer maps show strong shock fronts and a nuclear ring. There appears to be very little or no gas at the nucleus itself. Perpendicular to the bar, the shock fronts are barely resolved and extend <3 ''. Most of the molecular gas in the galaxy is in a central ellipse with a major axis of 3.5 kpc. This major axis and the strongest velocity gradients are perpendicular to the bar. Position-velocity diagrams are consistent with the molecular gas following elliptical orbits along the bar but show important deviations at the strong shock fronts and close to the nucleus, where the gas follows orbits perpendicular to the bar. We also detect giant molecular complexes near the ends of the bar and much fainter CO in molecular clouds in the southeast spiral arm. In spite of its high CO luminosity and great central concentration of molecular gas, the galaxy has only a modest L(FIR)/L(CO) ratio, which suggests a relatively low rate of star formation. Although the molecular gas has a latent capacity to fuel a large starburst, further infall to the center is probably hindered by the closed orbits 1.5 kpc from the nucleus. Hence, most of the gas cannot attain the critical density needed for a large starburst.