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J/AJ/130/968         SDSS-C4 cluster catalog                     (Miller+, 2005)

The C4 clustering algorithm: clusters of galaxies in the Sloan Digital Sky Survey. Miller C.J., Nichol R.C., Reichart D., Wechsler R.H., Evrard A.E., Annis J., McKay T.A., Bahcall N.A., Bernardi M., Boehringer H., Connolly A.J., Goto T., Kniazev A., Lamb D., Postman M., Schneider D.P., Sheth R.K., Voges W. <Astron. J., 130, 968-1001 (2005)> =2005AJ....130..968M
ADC_Keywords: Clusters, galaxy ; Redshifts ; Velocity dispersion Keywords: catalogs - galaxies: clusters: general Abstract: We present the C4 Cluster Catalog, a new sample of 748 clusters of galaxies identified in the spectroscopic sample of the Second Data Release (DR2, 2004AJ....128..502A) of the Sloan Digital Sky Survey (SDSS). The C4 cluster-finding algorithm identifies clusters as overdensities in a seven-dimensional position and color space, thus minimizing projection effects that have plagued previous optical cluster selection. The present C4 catalog covers ∼2600deg2 of sky and ranges in redshift from z=0.02 to 0.17. The mean cluster membership is 36 galaxies (with measured redshifts) brighter than r=17.7, but the catalog includes a range of systems, from groups containing 10 members to massive clusters with over 200 cluster members with measured redshifts. The catalog provides a large number of measured cluster properties including sky location, mean redshift, galaxy membership, summed r-band optical luminosity (Lr), and velocity dispersion, as well as quantitative measures of substructure and the surrounding large-scale environment. We use new, multicolor mock SDSS galaxy catalogs, empirically constructed from the ΛCDM Hubble Volume (HV) Sky Survey output, to investigate the sensitivity of the C4 catalog to the various algorithm parameters (detection threshold, choice of passbands, and search aperture), as well as to quantify the purity and completeness of the C4 cluster catalog. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 147 748 The SDSS-C4 cluster catalog (DR2)
See also: : SDSS Home Page Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 I4 --- SDSS-C4 Source SDSS C4 identification 6- 13 F8.4 deg RA1deg Right Ascension from Method 1 (J2000) (1) 15- 22 F8.4 deg DE1deg Declination from Method 1 (J2000) (1) 24- 31 F8.4 deg RA2deg Right Ascension from Method 2 (J2000) (1) 33- 40 F8.4 deg DE2deg Declination from Method 2 (J2000) (1) 42- 49 F8.4 deg RAbdeg Right Ascension of Brightest galaxy (J2000) (1) 51- 58 F8.4 deg DEbdeg Declination of Brightest galaxy (J2000) (1) 60- 66 F7.5 --- z Mean cluster redshift 68- 71 I4 km/s sigma Velocity dispersion (2) 73- 75 I3 --- Rich Richness 77- 88 E12.6 solLum Lr Summed r-band cluster luminosity (3) 90 I1 --- SCF [0,2] Structure Contamination Flag (4) 92- 95 F4.2 --- DS Dressler-Shectman substructure statistics (a low value indicates a significant substructure) 97-146 A50 --- ONames Other names (5)
Note (1): In decimal degrees. Method 1 uses the peak in the C4 density field as cluster centroid. Method 2 uses the luminosity-weighted mean centroid. Note (2): To convert to the rest-frame of the cluster, divide by 1+z. Note (3): Corrected for missed targets. Note (4): We define a "structure contamination flag" (SCF) to measure the degree of isolation in redshift space for each cluster. We assign an SCF based on the ratio of the standard deviation of the dispersions over the mean of the velocity dispersions. A cluster with SCF=0 has a ratio of less than 15%, whereas SCF=2 has a ratio >30%. Note (5): Matched to within 10 arcminute of the cluster centroid.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Marianne Brouty [CDS] 14-Nov-2005
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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