[VFK98] 6036 , the SIMBAD biblio

Using a magnitude-limited, spectroscopic survey of the X-ray-luminous galaxy cluster MS 1054-03, we isolate 153 cluster galaxies and measure MS 1054's redshift and velocity dispersion to be z=0.8307±0.0004 and σ_z=1156±82 km/s. The absorption-line, poststarburst (``E+A''), and emission-line galaxies, respectively, make up 63%±7%, 15%±4%, and 23%±4% of the cluster population. With photometry from HST ACS, we find that the absorption-line members define an exceptionally tight red sequence over a span of ∼3.5 mag in i₇₇₅: their intrinsic scatter in (V₆₀₆-i₇₇₅) color is only 0.048±0.008, corresponding to a (U-B)_z scatter of 0.041. Their color scatter is comparable to that of the ellipticals (σ_Vi=0.055±0.008), but measurably smaller than that of the combined E+S0 sample (σ_Vi=0.072±0.010). The color scatter of MS 1054's absorption-line population is approximately twice that of the ellipticals in Coma; this difference is consistent with passive evolution where most of the absorption-line members (>75%) formed by z∼2, and all of them by z∼1.2. For red members, we find a trend (>95% confidence) of weakening Hδ absorption with redder colors that we conclude is due to age: in MS 1054, the color scatter on the red sequence is driven by differences in mean stellar age of up to ∼1.5 Gyr. We also generate composite spectra and estimate that the average S0 in MS 1054 is ∼0.5-1 Gyr younger than the average elliptical; this difference in mean stellar age is mainly due to a number of S0's that are blue (18%) and/or are poststarburst systems (21%).