Rest frame Strömgren photometry (3500Å, 4100Å, 4750Å and 5500Å) is presented for 509 galaxies in 17 rich clusters between z = 0 and z = 1 as a test of color evolution. Our observations confirm a strong, rest frame, Butcher-Oemler effect where the fraction of blue galaxies increases from 20% at z = 0.4 to 80% at z = 0.9. We also find that a majority of these blue cluster galaxies are composed of normal disk or post-starbursts systems based on color criteria. When comparing our colors to the morphological results from HST imaging, we propose that the blue cluster galaxies are a population of latetype, LSB objects who fade and are then destroyed by the cluster tidal field. After isolating the red objects from Butcher-Oemler objects, we have compared the mean color of these old, non-star forming objects with SED models in the literature as a test for passive galaxy evolution in ellipticals. We find good agreement with single burst models which predict a mean epoch of galaxy formation at z = 5. Tracing the red envelope for ellipticals places the earliest epoch of galaxy formation at z = 10.

Narrow band photometry is presented on 27 dwarf ellipticals in the Fornax cluster. Calibrated with Galactic globular cluster data and spectrophotometric population models, the colors indicated that dwarf ellipticals have a mean [Fe/H] of −1.00 ± 0.28 ranging from −1.6 to −0.4. The mean age of dwarf ellipticals, also determined photometrically, is estimated at 10±1 Gyrs compared to 13 Gyrs for bright Fornax ellipticals. Comparison of our metallicity color and Mg 2 indices demonstrates that the [Mg/Fe] ratio is lower in dwarf ellipticals than their more massive cousins, which is consistent with a longer duration of initial star formation to explain their younger ages. There is a increase in dwarf metallicity with distance from the Fornax cluster center where core galaxies are, on average, 0.5 dex more metal-poor than halo dwarfs. In addition, we find the halo dwarfs are younger in mean age compared to core dwarfs. One possible explanation is that the intracluster medium ram pressure strips the gas from dwarf ellipticals halting star formation (old age) and stopping enrichment (low metallicity) as they enter the core.In order to relink the uz, vz, bz, yz system to the metallicity system defined by globular clusters, a series of metal-rich and metal-poor systems were observed between 1997 and 1999 from both the northern and southern hemisphere. The northern cluster observations were made at Lowell Observatory using 1.1m Hall telescope. The imaging device was the SIT 2K CCD with 24 micron pixels binned 4x4. The field size covers 18x18 arc minutes of sky. The southern cluster observations were made at CTIO using the 0.91m Curtis Schmidt telescope plus STIS 2K CCD with 21 micron pixels. The plate scale of 2.1 arcsec/pixel covers 76x76 arcmins of sky. Reduction followed standard CCD procedures (bias, flatfield, etc). Standard

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We have observed three fields of the Coma cluster of galaxies with a narrow band (modified Strömgren) filter system. Observed galaxies include 31 in the vicinity of NGC 4889, 48 near NGC 4874, and 60 near NGC 4839 complete to M 5500 = −18 in all three subclusters. Spectrophotometric classification finds all three subclusters of Coma to be dominated by red, E type (ellipticals/S0's) galaxies with a mean blue fraction, f B , of 0.10. The blue fraction increases to fainter luminosities, possible remnants of dwarf starburst population or the effects of dynamical friction removing bright, blue galaxies from the cluster population by mergers. We find the colormagnitude (CM) relation to be well defined and linear over the range of M 5500 = −13 to −22. The observational error is lower than the true scatter around the CM relation indicating that galaxies achieve their final positions in the mass-metallicity plane by stochastic processes. After calibration to multi-metallicity models, bright ellipticals are found to have luminosity weighted mean [Fe/H] values between −0.5 and +0.5, whereas low luminosity ellipticals have [Fe/H] values ranging from −2 to solar. The lack of CM relation in our continuum color suggests that a systematic age effect cancels the metallicity effects in this bandpass. This is confirmed with our age index (∆(bz − yz)) which finds a weak correlation between luminosity and mean stellar age in ellipticals such that the stellar populations of bright ellipticals are 2 to 3 Gyrs younger than low luminosity ellipticals. With respect to environmental effects, there is a slight decreasing metallicity gradient with respect to distance to each subcluster center, strongest around NGC 4874. Since NGC 4874 is the dynamic and x-ray center of the Coma cluster, this implies that environmental effects on low luminosity ellipticals are strongest at the cluster core compared to outlying subgroups.

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