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28 March 2024
 
  » arxiv » astro-ph/0408165

 Article overview


The Evolutionary Status of Clusters of Galaxies at z ~ 1
H. Ford ; M. Postman ; J.P. Blakeslee ; R. Demarco ; M.J. Jee ; P. Rosati ; B.P. Holden ; N. Homeier ; G. Illingworth ; R.L. White ;
Date 9 Aug 2004
Subject astro-ph
AbstractCombined HST, X-ray, and ground-based optical studies show that clusters of galaxies are largely "in place" by $z sim 1$, an epoch when the Universe was less than half its present age. High resolution images show that elliptical, S0, and spiral galaxies are present in clusters at redshifts up to $z sim 1.3$. Analysis of the CMDs suggest that the cluster ellipticals formed their stars several Gyr earlier, near redshift 3. The morphology--density relation is well established at $zsim1$, with star-forming spirals and irregulars residing mostly in the outer parts of the clusters and E/S0s concentrated in dense clumps. The intracluster medium has already reached the metallicity of present-day clusters. The distributions of the hot gas and early-type galaxies are similar in $zsim1$ clusters, indicating both have largely virialized in the deepest potentials wells. In spite of the many similarities between $zsim1$ and present-day clusters, there are significant differences. The morphologies revealed by the hot gas, and particularly the early-type galaxies, are elongated rather than spherical. We appear to be observing the clusters at an epoch when the sub-clusters and groups are still assembling into a single regular cluster. Support for this picture comes from CL0152 where the gas appears to be lagging behind the luminous and dark mass in two merging sub-components. Moreover, the luminosity difference between the first and second brightest cluster galaxies at $zsim1$ is smaller than in 93% of present-day Abell clusters, which suggests that considerable luminosity evolution through merging has occurred since that epoch. Evolution is also seen in the bolometric X-ray luminosity function.
Source arXiv, astro-ph/0408165
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