Deviations from the Fundamental Plane and the Peculiar Velocities of Clusters

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  • 24 March 1999
Abstract
We have fit the fundamental plane (FP) to early-type galaxies in 20 nearby clusters (4000 < cz < 11000 km/s) using our own photometry and spectroscopy as well as measurements culled from the literature. We find that the quality-of-fit to the average fundamental plane, , varies by a factor of two among these clusters. About half the clusters fit the well, 0.05 < r.m.s.[log(sigma)] < 0.07, while the rest do not, 0.08 < r.m.s.[log(sigma)] < 0.10. The peculiar velocity (PV) distribution of these two sets of clusters is distinctly different. The clusters with low scatter about the are found to be at rest with respect to the cosmic microwave background (CMB) within our measurement errors (250 km/s). Only clusters in the poor-fit group show large PVs, implying these velocities are artifacts of an improper fit, rather than true indications of physical motion. Furthermore, we find that all X-ray bright clusters in our sample fit the well, suggesting that early-type galaxies in the most massive, virialized clusters form a more uniform population than do cluster ellipticals as a whole.

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