A Keck Spectroscopic Survey of MS 1054–03 (z = 0.83): Forming the Red Sequence

• Published in: The Astrophysical journal 2007-06, Vol.661 (2), p.750-767
• Main Authors: Tran, Kim-Vy H, Franx, Marijn, Illingworth, Garth D, van Dokkum, Pieter, Kelson, Daniel D, Blakeslee, John P, Postman, Marc
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/513738

Using a magnitude-limited, spectroscopic survey of the X-ray-luminous galaxy cluster MS 1054-03, we isolate 153 cluster galaxis and measure MS 1054's redshift and velocity dispersion to be z = 0.8307 plus or minus 0.0004 and sigma sub(1) = 1156 plus or minus 82 km s super(-1). The absorption-line, poststarburst ("E+A"), and emission-line galaxies, respectively, make up 63% plus or minus 7%, 15% plus or minus 4%, and 23% plus or minus 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 similar to 3.5 mag in [unk]773: their Intrinsic scatter in (V sub(656) - [unk] sub(775)) color is only 0.048 plus or minus 0.008, corresponding to a (V - B) [unk] scatter of 0.041. Their color scatter is comparable to that of the ellipticals ( sigma v [unk] -0.055 plus or minus 0.008), but measurably smaller than that of the combined E+SO sample ( sigma v [unk] = 0.072 plus or minus 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 similar to 2, and all of them by z similar to 1.2. For red members, we find a trend (>95% confidence) of weakening H delta 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 similar to 1.5 Gyr. We also generate composite spectra and estimate that the average SO in MS 1054 is similar to 0.5-1 Gyr younger than the average elliptical; this difference in mean stellar age is mainly due to a number of SO's that are blue (18%) and/or are poststarburst systems (21%).