[Previous] | [Session 38] | [Next]
R. A. Gibbons (STScI \& U. Maryland), A. S. Fruchter (STScI), G. D. Bothun (U. Oregon)
We have fit the fundamental plane (FP) to elliptical galaxies in 20 nearby clusters (cz~~ 4000-11000~km~s-1), using our own photometry and spectroscopy as well as measurements culled from the literature. We find that the goodness-of-fit to an average fundamental plane (\overline{FP}) varies by more than a factor of two between these clusters. The sample is distinctly bimodal in r.m.s.\;: about half the clusters fit the \overline{FP} well, 0.05~<~r.m.s.[log(\sigma)]<~0.06, while the rest do not, 0.08~<~r.m.s.[log(\sigma)]<~0.11. The clusters with low scatter about the \overline{FP} are found to be at rest with respect to the cosmic microwave background (CMB) within our measurement errors (~250~km~s-1). Only poor-fit clusters show large peculiar velocities (PV's), implying inaccurate measurement, rather than true indications of large peculiar motions. Furthermore, we find that all x-ray bright clusters in our sample fit the \overline{FP} well, suggesting that in the most massive, virialized clusters the ellipticals form a more uniform sample.