2006/04/04 by Simona Mei, Brad P. Holden, John P. Blakeslee +11 · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Brightest cluster galaxy #Cluster (spacecraft) #Elliptical galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Population #Redshift #Stellar population #Stellar, planetary, and galactic studies #Supercluster (genetic) #astro-ph
paper · pdf · doi:10.1086/503826
published as Astrophys.J. 644 (2006) 759-768 · 22 pages, 8 figures; ApJ, in press
arxiv created 2006/04/04 · openalex publication_date 2006/06/19 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Color-magnitude relations (CMRs) have been derived in two high-redshift clusters, RX J0849+4452 and RX J0848+4453 (with redshifts of z = 1.26 and 1.27, respectively), that lie in the highest redshift cluster superstructure known today, the Lynx Supercluster. The CMR was determined from ACS imaging in the WFC F775W ( i 775 ) and F850LP ( z 850 ) filters combined with ground-based spectroscopy. Early-type cluster candidates have been identified according to the Postman et al. morphological classification. In both clusters the bright red early-type population defines a tight CMR very similar in color, although the two clusters present different X-ray luminosities and shapes. The elliptical galaxy CMRs in RX J0849+4452 and RX J0848+4453 show an intrinsic ( i 775 - z 850 ) color scatter of 0.026 ± 0.012 and 0.024 ± 0.015 mag, respectively, within 2' (~1 Mpc at z = 1.26) from the cluster X-ray emission centers. Simple modeling of the scatters using stellar population models from Bruzual and Charlot gives a mean luminosity-weighted age > 2.5 Gyr ( z f > 2.75) and > 2.6 Gyr ( z f > 2.8) for ellipticals in RX J0849+4452 and RX J0848+4453, respectively. S0 galaxies follow the elliptical CMR; they show larger scatters about the CMR. The intrinsic scatter decreases and the CMR slopes are steeper at smaller radii, within both clusters. Within 1' from the cluster X-ray emission centers, elliptical CMR scatters imply a mean luminosity-weighted age > 3.2 Gyr ( z f > 3.7). We conclude that old stellar populations in cluster elliptical galaxies are already in place at z = 1.26, both in the more evolved cluster RX J0849+4452 and in its less evolved companion RX J0848+4453. Even at a look-back time of 9 Gyr, in the early merging and buildup of massive clusters, the bulk of the stellar content of the bright elliptical galaxy population was in place—apparently formed some 2.5 Gyr earlier at z ~ 3.