Kinematics of Clusters in M33

Extract

We have obtained 9.5 A resolution spectrophotometry of 10 clusters in M33 (Cf. Christian and Schommer 1982) with the KPNO 4m telescope. Velocities were derived by comparing the cluster spectra to data for template stars, using the “Fourier quotient” technique described by Sargent et al (1977). The positions and velocities of the clusters are shown schematically in Figure 1, where the HI velocity map (Rogstad, et al 1976) is also indicated. We find that the velocities of younger, bluer clusters are more closely matched to the disk-like motion of the gas, while the older redder clusters have more discrepant values (Table I). As shown in Figure 2, Velocity difference, Vel (HI - cluster), varies smoothly with the integrated (B-V), suggesting a slow smooth collapse of M33 to a disk galaxy. This fall, we intend to increase our sample of measured cluster velocities to probe more completely the history of the cluster and disk formation in M33.