VLT AND ACS OBSERVATIONS OF RDCS J1252.9-2927: DYNAMICAL STRUCTURE AND GALAXY POPULATIONS IN A MASSIVE CLUSTER AT Z=1.237*

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We present results from an extensive spectroscopic survey, carried out with FORS on the ESO Very Large Telescope, and from an extensive multi-wavelength imaging data set from the Advanced Camera for Surveys and ground based facilities of the cluster of galaxies RDCS J1252.9-2927. We have spectroscopically confirmed 38 cluster members in the redshift range 1.22 < z < 1.25. The distribution in velocity of these spectroscopic members yields a cluster median redshift of z = 1.237 and a rest-frame velocity dispersion of 747{sub -84}{sup +74} km s{sup -1}. Star-forming members are observed to mainly populate the outskirts of the cluster ... continued below

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Demarco, R; Rosati, P; Lidman, C; Girardi, M; Nonino, M; Rettura, A et al. March 23, 2007.

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We present results from an extensive spectroscopic survey, carried out with FORS on the ESO Very Large Telescope, and from an extensive multi-wavelength imaging data set from the Advanced Camera for Surveys and ground based facilities of the cluster of galaxies RDCS J1252.9-2927. We have spectroscopically confirmed 38 cluster members in the redshift range 1.22 < z < 1.25. The distribution in velocity of these spectroscopic members yields a cluster median redshift of z = 1.237 and a rest-frame velocity dispersion of 747{sub -84}{sup +74} km s{sup -1}. Star-forming members are observed to mainly populate the outskirts of the cluster while passive galaxies dominate the central cluster region. Using the 38 confirmed redshifts, we were able to resolve, for the first time at z > 1, kinematic structure. The velocity distribution, which is not Gaussian at the 95% confidence level, is consistent with two groups that are also responsible for the projected elongation of the cluster in the East-West direction. The groups are composed of 26 and 12 galaxies and have velocity dispersions of 486{sub -85}{sup +47} km s{sup -1} and 426{sub -105}{sup +57} km s{sup -1}, respectively. The elongation is also seen in the intracluster gas (from X-ray observations) and the dark matter distribution (from a weak lensing analysis). This leads us to conclude that RDCS J1252.9-2927 has not yet reached a final virial state. We extend the analysis of the color-magnitude diagram of spectroscopic members to more than 1 Mpc from the cluster center. The scatter and slope of non-[OII]-emitting cluster members in the near-IR red sequence is similar to that seen in clusters at lower redshift. Furthermore, none of the galaxies with luminosities greater than {approx} K*{sub s} + 1.5 show any [OII] emission feature, indicating that these more luminous, redder galaxies have stopped forming stars earlier than the fainter, bluer galaxies. Our observations provide detailed dynamical and spectrophotometric information of galaxies in this exceptional high-redshift cluster, delivering an in-depth view of structure formation at this epoch only 5 Gyr after the Big Bang. In addition, we present the spectra of a few X-ray point sources in the cluster field of view.

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PDF-file: 41 pages; size: 7.2 Mbytes

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  • Journal Name: The Astrophysical Journal, vol. 663, no. 1, July 1, 2007, pp. 164-182; Journal Volume: 663; Journal Issue: 1

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  • Report No.: UCRL-JRNL-229399
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 940877
  • Archival Resource Key: ark:/67531/metadc893250

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  • March 23, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Dec. 9, 2016, 12:12 a.m.

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Demarco, R; Rosati, P; Lidman, C; Girardi, M; Nonino, M; Rettura, A et al. VLT AND ACS OBSERVATIONS OF RDCS J1252.9-2927: DYNAMICAL STRUCTURE AND GALAXY POPULATIONS IN A MASSIVE CLUSTER AT Z=1.237*, article, March 23, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc893250/: accessed December 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.