{
  "id": "astro-ph/0206442",
  "version": "v1",
  "published": "2002-06-25T20:54:06.000Z",
  "updated": "2002-06-25T20:54:06.000Z",
  "title": "Evidence for Cluster Evolution from an Improved Measurement of the Velocity Dispersion and Morphological Fraction of Cluster 1324+3011 at z = 0.76",
  "authors": [
    "Lori M. Lubin",
    "J. B. Oke",
    "Marc Postman"
  ],
  "comment": "22 pages, 7 figures; accepted for publication in Astronomical Journal",
  "doi": "10.1086/342542",
  "categories": [
    "astro-ph"
  ],
  "abstract": "We have carried out additional spectroscopic observations in the field of cluster Cl 1324+3011 at z = 0.76. Combined with the spectroscopy presented in Postman, Lubin & Oke (2001, AJ, 122, 1125), we now have spectroscopically confirmed 47 cluster members. With this significant number of redshifts, we measure accurately the cluster velocity dispersion to be 1016 (+126/-93) km/s. The distribution of velocity offsets is consistent with a Gaussian, indicating no substantial velocity substructure. As previously noted for other optically-selected clusters at redshifts of z > 0.5, a comparison between the X-ray luminosity (L_x) and the velocity dispersion (sigma) of Cl 1324+3011 implies that this cluster is underluminous in X-rays by a factor of ~3 - 40 when compared to the L_x - sigma relation for local and moderate-redshift clusters. We also examine the morphologies of those cluster members which have available high-angular-resolution imaging with the Hubble Space Telescope (HST). There are 22 spectroscopically-confirmed cluster members within the HST field-of-view. Twelve of these are visually classified as early-type (elliptical or S0) galaxies, implying an early-type fraction of 0.55 (+0.17/-0.14) in this cluster. This fraction is a factor of ~1.5 lower than that observed in nearby rich clusters. Confirming previous cluster studies, the results for cluster Cl 1324+3011, combined with morphological studies of other massive clusters at redshifts less than z = 1, suggest that the galaxy population in massive clusters is strongly evolving with redshift. This evolution implies that early-type galaxies are forming out of the excess of late-type (spiral, irregular, and peculiar) galaxies over the ~7 Gyr timescale.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2002-06-25T20:54:06.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cluster evolution",
      "morphological fraction",
      "cluster members",
      "cluster cl",
      "measurement"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 22,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 589255
    }
  }
}