Rotation curves for spiral galaxies in clusters. II - Variations as a function of cluster position

Rotation curves of spiral galaxies in clusters are examined using three criteria: (1) inner and outer velocity gradients; (2) residuals from synthetic rotation curves for field spirals; and (3) M/L gradients. A good correlation is found between the outer gradient of the rotation curve and the galaxy's distance from the center of the cluster, in the sense that the inner galaxies tend to have falling rotation curves, while the outer galaxies, and field galaxies, tend to have flat or rising rotation curves. A similar effect is seen in the residuals between the observed and synthetic rotation curves. A correlation is also found between the M/L gradient across a galaxy and the galaxy's position in the cluster, with the outer galaxies having steeper M/L gradients. An attempt to construct mass models produced inconclusive results. These correlations indicate that the inner cluster environment can strip away some fraction of the mass in the outer halo of a spiral galaxy or, alternatively, may not allow the halo to form.