SPIDERS: The spectroscopic follow-up of X-ray-selected clusters of galaxies in SDSS-IV

N. Clerc, A. Merloni, Y. Y. Zhang, A. Finoguenov, T. Dwelly, K. Nandra, C. Collins, K. Dawson, J. P. Kneib, E. Rozo, E. Rykoff, T. Sadibekova, J. Brownstein, Y. T. Lin, J. Ridl, M. Salvato, A. Schwope, M. Steinmetz, H. J. Seo, J. Tinker

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47 Scopus citations


SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a programme dedicated to the homogeneous and complete spectroscopic follow-up of X-ray active galactic nuclei and galaxy clusters over a large area (~7500 deg2) of the extragalactic sky. SPIDERS is part of the Sloan Digital Sky Survey (SDSS)-IV project, together with the Extended Baryon Oscillation Spectroscopic Survey and the Time-Domain Spectroscopic Survey. This paper describes the largest project within SPIDERS before the launch of eROSITA: an optical spectroscopic survey of X-ray-selected, massive (~1014-1015M) galaxy clusters discovered in ROSAT and XMM- Newton imaging. The immediate aim is to determine precise (Δz ~ 0.001) redshifts for 4000- 5000 of these systems out to z~0.6. The scientific goal of the program is precision cosmology, using clusters as probes of large-scale structure in the expanding Universe. We present the cluster samples, target selection algorithms and observation strategies. We demonstrate the efficiency of selecting targets using a combination of SDSS imaging data, a robust red-sequence finder and a dedicated prioritization scheme. We describe a set of algorithms and workflow developed to collate spectra and assign cluster membership, and to deliver catalogues of spectroscopically confirmed clusters. We discuss the relevance of line-of-sight velocity dispersion estimators for the richer systems. We illustrate our techniques by constructing a catalogue of 230 spectroscopically validated clusters (0.031 < z < 0.658), found in pilot observations. We discuss two potential science applications of the SPIDERS sample: the study of the X-ray luminosity-velocity dispersion (LX-σ) relation and the building of stacked phase-space diagrams.

Original languageEnglish (US)
Pages (from-to)4490-4515
Number of pages26
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Dec 21 2016


  • Catalogues
  • Cosmology: observations
  • Galaxies: clusters: general
  • X-rays: galaxies: clusters

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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