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The CNOC1 Cluster Survey
The CNOC1 Cluster Survey targeted 16 rich X-ray selected galaxy clusters at 0.17 < z < 0.55.  Observations were made from Jan 1993 to Mar 1995 using the CFHT Multi-Object-Spectrograph (MOS). Gunn g and r images to r>24 and spectroscopy to r=21.5-23, depending on the cluster redshift, were obtained. A total of ~1200 cluster redshifts to cluster-centric radii of up to 3 Mpc and ~1000 field redshifts were identified. The raw data are now available publicly and can be accessed via the CFHT Archive at the  Canadian Astronomical Data Center (CADC).

Synopsis of Results

The main goal of CNOC1 was to measure Omega, the total mass density of the universe relative to the closure density. Galaxy cluster virial masses and total luminosities were calculated from ~1200 cluster redshifts, yielding the cluster mass-to-light ratio M/L. ~1000 field galaxies from the same dataset, with the same corrections, yield the ratio of the closure density rho to the total field luminosity density j. Omega is then simply (M/L)/(rho/j). After minor corrections and crosschecks, Omega=0.19 +-0.06 (random) +-0.04 (estimated systematic).

  Flowchart for Finding Omega_M Using the CNOC1 Survey

CNOC1 Papers

Observational Details on CNOC1 Clusters

 Cluster z N cluster members* Velocity dispersion (km/sec)*  Number of masks **
Abell 2390 0.23 178 1093 CA,CB,CC,E1A,E1B,W1A,W1B,E2A.W2A,W2B
MS0016+16 0.55 47 1234 CA, CB
MS0302+16 0.42 27 646 CA, CB
MS0440+02 0.20 36 606 CA, CB, E1A, E1B, W1A, W1B
MS0451+02 0.20 113 988 CA0, CA, CB, CC, E1A, e1Aa, E1B, W1A, W1B,E2A, E2 (image only)
MS0451-03 0.54 51 1371 CA, CB
MS0839+29 0.19 44 749 CA, CB,E1A,W1A,W1B,W2A,W2B
MS0906+11 0.17 81 binary system CA,CB,CC
MS1006+12 0.26 26 906 CA,CB
MS1008-12 0.26 67 1054 CA,CB, N (image only), S(image only)
MS1224+20 0.33 24 802 CA,CB
MS1231+15 0.26 74 667 CA,CB,CC,N1A,S1A
MS1358+62 0.33 164 937 CA,CB,NA,SA,SB
MS1455+22 0.26 50 1133 CA,CB
MS1512+36 0.37 38 690 CA,CB,EA,EB,WA,WB
MS1621+26 0.43 98 793 CA,CB,NA,SA,SB

*From Carlberg et al. 1996 (ApJ 462, 32)
**Each slightly overlapping field covers a region 8x9 arcminutes. Field positions are designated C=central, E1=first east field, etc., and multiple masks per field are designated A,B,C. A total of 71 masks were observed over 24 nights, with ~3 nights lost to weather.

The published CNOC data (on clusters A2390, MS0015, MS0302, MS0451S, MS1008, MS1224, MS1358, MS1512, and MS1621) is available as a gzipped tar file.

If you are interested in using our database, please read the relevant technique and data papers to see completeness rates and selection effects. Within the cluster, there is very little selection effect due to galaxy color, but a mganitude and geometric weighting scheme is necessary to construct a representative sample of objects. CNOC1 field samples are strongly affected by selection effects from the limited bandpass used; CNOC2 should provide a much more robust sample.

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