KINEMATICS OF THE GAS IN A BARRED GALAXY: DO STRONG SHOCKS INHIBIT STAR FORMATION?

Denis Reynaud and Dennis Downes
Institut de Radio Astronomie Millimétrique, F-38406 Saint Martin d'Hères, France

Abstract: We present new CO(1-0) maps of the barred spiral galaxy NGC1530 with a resolution of 5''.3, obtained by adding short spacing visibilities from the IRAM 30m telescope to data from the IRAM interferometer. The improvement in sensitivity is spectacular, allowing us to detect with high signal-to-noise the extended CO lanes along the bar of the galaxy. These molecular gas lanes, which are density waves or shocks created by the barred potential, show a remarkable kinematic pattern. We find 50 to outward motions upstream of the lanes, and 70 to inward motions in and downstream of the lanes. The intensity of the shocks is greatest near the central CO concentration, and decreases to zero at the ends of the bar. We compare these kinematic features with a map of the H distribution that traces young stars. Star formation is very intense around the nucleus of the galaxy and at the ends of the bar. It is weak halfway between these extremities. In general, the HII regions are downstream of the CO lanes. The star formation is probably inhibited in the lanes at the places where the shocks and the shear are too strong. There may be a maximum threshold of 80 to for the relative velocity of any cloud entering the density wave, above which the cloud cannot form stars.
Accepted by Astronomy & Astrophysics.
e-mail : reynaud@iram.fr