[Paper Review] Optical Surveys for Galaxy Clusters

H. K. C. Yee, M. D. Gladders|ArXiv.org|Nov 21, 2001

Astronomy and Astrophysical Research3 citations

TL;DR

This paper introduces the red-sequence method using two-filter optical imaging to detect galaxy clusters in 3D space, eliminating projection contamination. The Red-Sequence Cluster Survey (RCS) successfully identifies high-redshift clusters (z ≈ 0.5–1.4), including multiple strong lensing arcs, demonstrating that wide-field optical surveys with 4m telescopes are highly efficient for creating well-defined, mass-complete cluster catalogs at z > 0.5.

ABSTRACT

We present a brief review of the history of optical searches of galaxy clusters, starting from that of Abell. The traditional application of this survey method suffers from contamination due to projection of galaxies along the line of sight, which becomes increasingly more severe at higher redshift. The new generation of wide-field CCD imagers has provided a renewed impetus for optical surveys for clusters. We describe a new cluster finding technique using the red sequence of early-type galaxies in galaxy groups and clusters, which eliminates the projection problem by essentially producing a 3-D distribution of red galaxies using two-filter imaging data. The Red-Sequence Cluster Survey (RCS) is a 100 square degree optical survey, carried out using 4m class telescopes, which is optimally designed to search for clusters at $0.5

Motivation & Objective

• To overcome the projection contamination problem in traditional optical cluster surveys, which severely limits high-redshift detection.
• To develop a 3D cluster detection method using the red sequence of early-type galaxies as a distance indicator.
• To demonstrate the feasibility and efficiency of wide-field optical surveys with 4m telescopes for discovering massive clusters at z > 0.5.
• To produce a well-defined, mass-complete catalog of galaxy clusters at high redshift using photometric redshifts and richness estimators.
• To enable cosmological constraints on Ωm and σ8 by deriving cluster mass functions from the survey data.

Proposed method

• Utilizes two-band optical imaging (e.g., R and I filters) to identify the red sequence of early-type galaxies in galaxy groups and clusters.
• Applies color-magnitude selection to isolate red sequence galaxies, which are used as distance indicators to distinguish true 3D overdensities from line-of-sight projections.
• Employs the richness parameter Bgc (from Yee & López-Cruz 1999) as a proxy for cluster mass, calibrated using the CNOC1 cluster sample.
• Uses photometric redshifts derived from color-magnitude data to estimate cluster redshifts and physical properties.
• Applies selection function corrections and simulations to derive cluster mass functions and cosmological constraints.
• Leverages high-quality, wide-field imaging from 4m telescopes (e.g., CFHT) to achieve deep, large-area coverage.

Experimental results

Research questions

• RQ1 Can the red-sequence method effectively eliminate projection contamination in optical cluster surveys at high redshift?
• RQ2 How efficient is wide-field two-filter imaging with 4m telescopes in detecting massive galaxy clusters at z > 0.5?
• RQ3 What is the detectability of strong lensing arcs in high-redshift clusters identified via the red-sequence method?
• RQ4 Can photometric redshifts and richness parameters be used to derive reliable cluster mass functions for cosmological constraints?
• RQ5 To what extent does optical cluster detection miss X-ray luminous clusters compared to X-ray surveys?

Key findings

• The Red-Sequence Cluster Survey (RCS) successfully detects galaxy clusters down to masses of ~10^14 M⊙ at redshifts between 0.5 and 1.4.
• The survey identifies multiple clusters with strong lensing arcs, including a rare system with two distinct arcs at different redshifts, one at z = 4.879.
• Spectroscopic follow-up of a high-redshift arc (z = 4.879) reveals a Lyα emission line with a velocity width < 50 km s⁻¹, suggesting a compact, highly magnified source.
• The RCS achieves a high detection efficiency for massive clusters using shallow two-filter imaging, requiring only ~10^4 seconds of integration per cluster.
• The survey’s mass function derived from two patches shows consistent constraints on the (Ωm, σ8) parameter pair, validating its cosmological utility.
• The method proves robust: Donahue et al. (2001) found no evidence that optical selection misses X-ray luminous clusters, confirming its completeness.