J/ApJ/746/178 The augmented maxBCG cluster catalog (Rykoff+, 2012)
Robust optical richness estimation with reduced scatter.
Rykoff E.S., Koester B.P., Rozo E., Annis J., Evrard A.E., Hansen S.M.,
Hao J., Johnston D.E., McKay T.A., Wechsler R.H.
<Astrophys. J., 746, 178 (2012)>
=2012ApJ...746..178R 2012ApJ...746..178R
ADC_Keywords: Clusters, galaxy ; X-ray sources ; Redshifts ; Spectroscopy
Keywords: galaxies: clusters: general - methods: data analysis -
X-rays: galaxies: clusters
Abstract:
Reducing the scatter between cluster mass and optical richness is a
key goal for cluster cosmology from photometric catalogs. We consider
various modifications to the red-sequence-matched filter richness
estimator of Rozo et al. (Paper I, 2009ApJ...703..601R 2009ApJ...703..601R) implemented on
the maxBCG cluster catalog and evaluate the impact of these changes on
the scatter in X-ray luminosity (LX) at fixed richness, using LX
from the ROSAT All-Sky Catalog as the best mass proxy available for
the large area required. Most significantly, we find that deeper
luminosity cuts can reduce the recovered scatter, finding that
σlnLx|λ=0.63±0.02 for clusters with
M500c≳1.6x1014h-170M☉. The corresponding scatter in
mass at fixed richness is σlnM|λ∼0.2-0.3 depending on
the richness, comparable to that for total X-ray luminosity. We find
that including blue galaxies in the richness estimate increases the
scatter, as does weighting galaxies by their optical luminosity. We
further demonstrate that our richness estimator is very robust.
Specifically, the filter employed when estimating richness can be
calibrated directly from the data, without requiring a priori
calibrations of the red sequence. We also demonstrate that the
recovered richness is robust to up to 50% uncertainties in the galaxy
background, as well as to the choice of photometric filter employed,
so long as the filters span the 4000Å break of red-sequence
galaxies. Consequently, our richness estimator can be used to compare
richness estimates of different clusters, even if they do not share
the same photometric data. Appendix A includes "easy-bake"
instructions for implementing our optimal richness estimator, and we
are releasing an implementation of the code that works with Sloan
Digital Sky Survey data, as well as an augmented maxBCG catalog with
the λ richness measured for each cluster.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 50 13823 maxBCG cluster catalog with λ richness
code/* . 2 IDL code and corresponding ReadMe files
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
J/ApJ/703/2217 : SDSS galaxy clusters. I. (Sheldon+, 2009)
J/ApJ/684/905 : Galaxy clusters from IRAC Shallow Survey (Eisenhardt+, 2008)
J/ApJ/660/239 : MaxBCG cat.: 13823 galaxy clusters from SDSS (Koester+, 2007)
J/A+A/423/449 : RASS-SDSS Galaxy Clusters Survey. I. (Popesso+, 2004)
J/A+A/425/367 : REFLEX Galaxy Cluster Survey catalogue (Boehringer+, 2004)
J/ApJS/129/435 : NORAS galaxy cluster survey. I. (Bohringer+, 2000)
J/MNRAS/318/333 : Extended ROSAT Bright Cluster Sample (Ebeling+ 2000)
J/MNRAS/301/881 : The ROSAT brightest cluster sample - I. (Ebeling+, 1998)
http://www.sdss.org/ : SDSS Web site
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000) (1)
11- 20 F10.6 deg DEdeg Declination in decimal degrees (J2000) (1)
22- 26 F5.3 --- zph [0.103/0.3] Photometric redshift (1)
28- 33 F6.3 --- zsp [-1/0.556] BCG spectroscopic redshift (2)(3)
35- 37 I3 --- N200 [10/188] max BCG Richness estimator (1)(4)
39- 44 F6.2 --- lambda [-2/217.39] Matched filter richness (2)
46- 50 F5.2 --- e_lambda [-2/6.22] Error estimate in lambda (2)
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Note (1): The positions, photometric redshifts, and original richness estimate
(N200) are taken directly from Table 1 in Koester et al. (2007,
Cat. J/ApJ/660/239; <[KMA2007] DDD.ddddd+DD.ddddd> for Simbad).
Note (2): We set zBCGspec=-1.0 when a spectrum is not available, and set
λ=-1.0 when no significant number of red galaxies above
background is found by the richness estimator. In addition, we note
that the DR7 galaxy catalog used to calculate λ covers a
slightly different footprint than the original DR4 catalog used to
construct the original maxBCG catalog. There are 80 maxBCG clusters
that we cannot calculate reliable richness estimates as they are in
newly masked regions. For these, we set λ=-2.0 in the catalog.
See section 3 for further explanations of λ and tar file for
the IDL code that will calculate λ for SDSS data.
Note (3): The spectroscopic redshifts (zBCGspec) are obtained by
cross-identifying the maxBCG BCG positions with the full spectroscopic
catalog from SDSS DR8, thus increasing the number of BCGs with spectra
from 5413 to 9409.
Note (4): The richness estimator used in the maxBCG catalog is N200, defined
as the number of galaxies with g-r colors within 2σ of the E/S0
ridgeline as defined by the brightest cluster galaxy (BCG) color, that
are brighter than 0.4L* (in i band), and found within a scaled
aperture rgal200 of the cluster center.
See section 2.1 for further details.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 17-Sep-2013