AAS 201st Meeting, January, 2003
Session 59. Structure in and at Clusters of Galaxies
Oral, Tuesday, January 7, 2003, 10:00-11:30am, 606-607

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[59.08] ACS Observations of a Rich Cluster of Galaxies at z = 1.23

M. Postman (STScI), P. Rosati (ESO), H. Ford, J. Blakeslee (JHU), G. Illingworth (UCSC), M. Franx (Leiden), ACS Investigation Definition Team

In May 2002, deep images were obtained with HST's new Advanced Camera for Surveys (ACS) of CL1252-2927 (z=1.23). This is one of the most distant, spectroscopically confirmed rich clusters known. The cluster is also an extended x-ray source. The observations are part of our GTO cluster survey that aims to establish new constraints on the evolution and formation of clusters and cluster galaxies. The high sensitivity and angular resolution of the wide-field camera (WFC) on ACS has provided dramatic images over the central 2.5 Mpc region of this cluster. The data consist of deep F775W (SDSS-i) and F850LP (SDSS-z) images taken in 4 partially overlapping pointings. The central 1 arcminute of the cluster is imaged in all 4 pointings, yielding an ultra-deep image (i=28, 5 sigma) of this area.

The red sequence is easily detected in the i-z color-magnitude diagram and is centered at i-z = 1.0 and extends down to at least i=26 mag. We will present the ACS/WFC imagery of CL1252-2927 along with preliminary results on the slope and scatter of the color-magnitude relation of the cluster red sequence along with estimates of the morphological composition of these galaxies.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.