Browsing by Author "Gilbank, David G."

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    A z=0.9 supercluster of X-ray luminous, optically selected, massive galaxy clusters
    (2008) Gilbank, David G.; Yee, H. K. C.; Ellingson, E.; Hicks, A. K.; Gladders, M. D.; Barrientos, L. F.; Keeney, B.
    We report the discovery of a compact supercluster structure at z = 0.9. The structure comprises three optically selected clusters, all of which are detected in X- rays and spectroscopically confirmed to lie at the same redshift. The Chandra X-ray temperatures imply individual masses of similar to 5 x 10(14) M-circle dot. The X-ray masses are consistent with those inferred from optical-X-ray scaling relations established at lower redshift. A strongly lensed z similar to 4 Lyman break galaxy behind one of the clusters allows a strong-lensing mass to be estimated for this cluster, which is in good agreement with the X-ray measurement. Optical spectroscopy of this cluster gives a dynamical mass in good agreement with the other independent mass estimates. The three components of the RCS 2319 + 00 supercluster are separated from their nearest neighbor by a mere < 3 Mpc in the plane of the sky and likely ! 10 Mpc along the line of sight, and we interpret this structure as the high-redshift antecedent of massive (similar to 10(15) M) clusters such as MS 0451.5 - 0305.
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    The red-sequence luminosity function in galaxy clusters since z ∼ 1
    (2008) Gilbank, David G.; Yee, H. K. C.; Ellingson, E.; Gladders, M. D.; Loh, Y. -S.; Barrientos, L. F.; Barkhouse, W. A.
    We use a statistical sample of similar to 500 rich clusters taken from 72 deg(2) of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of similar to 30,000 red-sequence galaxies in clusters over the redshift range 0.35 < z < 0.95. We construct red-sequence luminosity functions (RSLFs) for a well-defined, homogeneously selected, richness-limited sample. The RSLF at higher redshifts shows a deficit of faint red galaxies (to M-V >= -19.7) with their numbers increasing toward the present epoch. This is consistent with the "downsizing" picture in which star formation ended at earlier times for the most massive (luminous) galaxies and more recently for less massive (fainter) galaxies. We observe a richness dependence to the downsizing effect in the sense that, at a given redshift, the drop-off of faint red galaxies is greater for poorer (less massive) clusters, suggesting that star formation ended earlier for galaxies in more massive clusters. The decrease in faint red-sequence galaxies is accompanied by an increase in faint blue galaxies, implying that the process responsible for this evolution of faint galaxies is the termination of star formation, possibly with little or no need for merging. At the bright end, we also see an increase in the number of blue galaxies with increasing redshift, suggesting that termination of star formation in higher mass galaxies may also be an important formation mechanism for higher mass ellipticals. By comparing with a low-redshift Abell cluster sample, we find that the downsizing trend seen within RCS-1 has continued to the local universe.