CO Distribution and Kinematics along the Bar in the Strongly Barred Spiral NGC 7479

We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observationscovering the whole length of the bar in the strongly barred late-type spiralgalaxy NGC 7479. CO emission is detected only along a dust lane that traversesthe whole length of the bar, including the nucleus. The emission is strongestin the nucleus. The distribution of emission is clumpy along the bar outsidethe nucleus, and consists of gas complexes that are unlikely to begravitationally bound. The CO kinematics within the bar consist of two separatecomponents. A kinematically distinct circumnuclear disk, < 500 pc in diameter,is undergoing predominantly circular motion with a maximum rotational velocityof 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the baroutside the circumnuclear disk has substantial noncircular motions which areconsistent with a large radial velocity component, directed inwards. The COemission has a large velocity gradient across the bar dust lane, ranging from0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocitychange across the dust lane is as high as 200 km/s. This sharp velocitygradient is consistent with a shock front at the location of the bar dust lane.A comparison of H-alpha and CO kinematics across the dust lane shows thatalthough the H-alpha emission is often observed both upstream and downstreamfrom the dust lane, the CO emission is observed only where the velocitygradient is large. We also compare the observations with hydrodynamic modelsand discuss star formation along the bar.Comment: 16 pages, including 10 figures. Accepted for publication in Ap