Spectroscopic characterization of galaxy clusters in RCS-1: Spectroscopic confirmation, redshift accuracy, and dynamical mass-richness relation

David G. Gilbank, L. Felipe Barrientos, Erica Ellingson, Kris Blindert, H. K.C. Yee, T. Anguita, M. D. Gladders, P. B. Hall, G. Hertling, L. Infante, R. Yan, M. Carrasco, Cristina Garcia-Vergara, K. S. Dawson, C. Lidman, T. Morokuma

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


We present follow-up spectroscopic observations of galaxy clusters from the first Red-sequence Cluster Survey (RCS-1). This work focuses on two samples, a lower redshift sample of ~30 clusters ranging in redshift from z~0.2-0.6 observedwith multiobject spectroscopy (MOS) on 4-6.5-m class telescopes and a z ~ 1 sample of ~10 clusters 8-m class telescope observations. We examine the detection efficiency and redshift accuracy of the now widely used redsequence technique for selecting clusters via overdensities of red-sequence galaxies. Using both these data and extended samples including previously published RCS-1 spectroscopy and spectroscopic redshifts from SDSS, we find that the red-sequence redshift using simple twofilter cluster photometric redshifts is accurate to σz ≈ 0.035(1 + z) in RCS-1. This accuracy can potentially be improved with better survey photometric calibration. For the lower redshift sample, ~5 per cent of clusters show some (minor) contamination from secondary systems with the same red-sequence intruding into the measurement aperture of the original cluster. At z ~ 1, the rate rises to ~20 per cent. Approximately ten per cent of projections are expected to be serious, where the two components contribute significant numbers of their red-sequence galaxies to another cluster. Finally, we present a preliminary study of the mass-richness calibration using velocity dispersions to probe the dynamical masses of the clusters. We find a relation broadly consistent with that seen in the local universe from the WINGS sample at z ~ 0.05.

Original languageEnglish
Pages (from-to)1991-2012
Number of pages22
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - May 11 2018

Bibliographical note

Publisher Copyright:
© 2018 The Author(s).


  • Galaxies: clusters: general
  • Galaxies: distances and redshifts

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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