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 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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 147 748 The SDSS-C4 cluster catalog (DR2)
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See also:
http://www.sdss.org : SDSS Home Page
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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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)
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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.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Marianne Brouty [CDS] 14-Nov-2005