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Session 51 - Galaxy Evolution and the Intergalactic Medium.
Display session, Wednesday, June 10
Atlas Ballroom,

[51.03] Evidence for an Environmental Dependence of the E/S0 Ridgeline

C. Stoughton, J. Annis, D. L. Tucker (Fermilab Experimental Astrophysics Group), Y. Hashimoto (Yale/OCIW), T. A. McKay, J. A. Smith (U. Michigan Physics Dept.)

The Las Campanas Redshift Survey (LCRS) is a galaxy survey which extends to a redshift of 0.2 and which is composed of 6 alternating 1.5^\circ \times 80^\circ slices -- 3 each in the two galactic caps. Completed in 1996, the LCRS contains approximately 26,400 galaxy redshifts. b_J-band photometry from the Automated Plate Measuring Machine (APM) Galaxy Survey, LCRS R-band photometry, and multi-band CCD photometry of many of the fields permit the derivation of rest-frame colors for much of the LCRS Southern Galactic Cap sample. A "friends-of-friends" group-finding algorithm has been used to break this color sample into three additional subsets: galaxies in groups, galaxies in clusters, and galaxies in the richest clusters. Taking the galaxy concentration index data of Hashimoto et al. (1998), we were able to extract E/S0 ridgelines for these samples. Plotting color vs. M_R for the different samples' ridgelines, we have found that the slope of this relation becomes progressively steeper as one goes from the full sample (which has no significant slope) to one containing only galaxies in the richest clusters. We explain this environmental dependence in terms of stronger feedback of processed stellar material in star formation within cluster galaxies.

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