THE CHEMICAL EVOLUTION OF A GALACTIC DISC WITH INFALL AND RADIAL MOTIONS .2. DEPARTURES FROM CENTRIFUGAL EQUILIBRIUM

If a galactic disc is formed by infall of matter which possesses inapp ropriate specific angular momentum for circular orbit at its initial r adial position, the matter will move radially to achieve centrifugal e quilibrium. We solve the equations leading to such equilibrium in the inner regions of the disc. We find that the approach is rapid, and tha t few stars form on significantly non-circular orbits. The outer regio n of the disc, where departures from centrifugal equilibrium remain si gnificant, contains little mass in the form of either gas or stars. Wi th a star formation rate proportional to the square of the gas surface density, radial abundance gradients are produced which are somewhat l ower than those typically observed for H II regions in spiral galaxies . The gradients are, however, significantly greater than those obtaine d when radial flows are absent.