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Session 110 - Imaging of Cluster Galaxies.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
We present preliminary results from an investigation into the evolution of elliptical galaxies in five clusters at 0.08 < z < 0.37, corresponding to look-back times of up to one-third of the present age of the universe. In each cluster, we have used two-color optical imaging to identify a complete sample of the early-type galaxy population. For a subsample of 15--25 galaxies per cluster, we have measured the K-band photometric parameters of radius and surface brightness (SB), and the internal stellar velocity dispersions and metal-line indices at moderate spectral resolution (corresponding to instrumental FWHM resolutions between 120 and 180 km s^-1) using the multiobject spectrographs on both the Keck 10 m and the Palomar 5 m telescopes. We have constructed the near-infrared Fundamental Plane (FP) for each cluster. The SB intercept of the FP relations is a sensitive probe of the passive evolution of elliptical galaxies. Our results are fully consistent with simple stellar populations models of passive evolution for the cluster elliptical galaxy population, and are inconsistent at high significance with a non-expanding universal model thereby providing the best example of the Tolman SB cosmological test to date. The slopes of the FP relations and the intrinsic scatter around them are sensitive to stellar populations variations among the ellipticals, and also to variations among the internal dynamical structures of the family of cluster elliptical galaxies. Our results suggest that these cluster ellipticals are coeval and formed at high redshift.
