Session 102 - Clusters of Galaxies.
Display session, Thursday, January 16
Metropolitan Ballroom,

## [102.05] The Intrinsic Precision in the D_n-\sigma Relation and Evidence for Substructure in the Coma Cluster

M. J. Pierce, R. Tripoli (Indiana Univ.)

We present new redshifts and velocity dispersions for 42 elliptical galaxies in the Coma Cluster acquired with the multiobject spectrograph (Hydra) on the WIYN 3.5-m telescope. The spectra were obtained at a dispersion of 0.48 Åpixel enabling high-precision velocity dispersion measurements. We also present new I-band photometric data acquired with the KPNO 2.1-m telescope. These data are combined to form the D_n-\sigma relation. We find that the majority of the galaxies are found along a ridge-line'' with a scatter of only 5% in distance. The velocity-distance relation indicates that those galaxies forming the ridge-line'' also have a high velocity dispersion, while the remaining systems are generally found in a foreground group with low velocity dispersion. Evidently, the intrinsic precision of the D_n-\sigma relation for elliptical galaxies is significantly higher than previously believed. We briefly discuss the prospects for obtaining high-precision, redshift-independent distances at z = 0.1.