The L_X-M relation of Clusters of Galaxies Page: 1 of 6
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The Lx-M Relation of Clusters of Galaxies
E. S. Rykoff,1 A. E. Evrard,2 3 4 T. A. McKay,2 3 4 M. R. Becker,2 5 D. E. Johnston,6
B. P. Koester,7 8 B. Nord,2 E. Rozo,9 E. S. Sheldon,10 R. Stanek,3 R. H. Wechsler"
1 TABASCO Fellow, Physics Department, University of California at Santa Barbara, 2233B Broida Hall, Santa Barbara, CA 93106
2 Physics Department, University of Michigan, Ann Arbor, MI 48109
3Astronomy Department, University of Michigan, Ann Arbor, MI 48109
4Michigan Center for Theoretical Physics, Ann Arbor, MI 48109
5Department of Physics, The University of Chicago, Chicago, IL 60637
6 Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109
7Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637
8Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, IL 60637
9 CCAPP Fellow, The Ohio State University, Columbus, OH 43210
10 Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003
11KIPAC, Physics Dept. and SLAC, Stanford University, Stanford, CA 94305
Draft: February 7, 2007
We present a new measurement of the scaling relation between X-ray luminos-
ity and total mass for 17,000 galaxy clusters in the maxBCG cluster sample. Stack-
ing sub-samples within fixed ranges of optical richness, N2oo, we measure the mean
0.1-2.4 keV X-ray luminosity, (Lx), from the ROSAT All-Sky Survey. The mean
mass, (M2oo), is measured from weak gravitational lensing of SDSS background galax-
ies (Johnston et al. 2007). For 9 <; N2oo < 200, the data are well fit by a power-law,
(Lx)/1042 h-2 ergs-- (12.6 (stat) 1.6 (sys)) ((M2oo)/1014 h-1 M )1.65o13.
The slope agrees to within 10% with previous estimates based on X-ray selected cata-
logs, implying that the covariance in Lx and N2oo at fixed halo mass is not large. The
luminosity intercept is 30%, or 2a, lower than determined from the X-ray flux-limited
sample of Reiprich & Bdhringer (2002), assuming hydrostatic equilibrium. This slight
difference could arise from a combination of Malmquist bias and/or systematic error
in hydrostatic mass estimates, both of which are expected. The intercept agrees with
that derived by Stanek et al. (2006) using a model for the statistical correspondence
between clusters and halos in a WMAP3 cosmology with power spectrum normaliza-
tion a8 0.85. Similar exercises applied to future data sets will allow constraints on
the covariance among optical and hot gas properties of clusters at fixed mass.
Key words: clusters: general clusters: ICM X-rays: clusters clusters: calibration
Bulk properties of galaxy clusters, such as galaxy richness
and velocity dispersion, X-ray temperature and luminosity,
mean weak gravitational lensing shear and X-ray hydrostatic
mass, display strong internal correlations (for reviews, see
Rosati et al. 2002; Voit 2005). Although these correlations
are anticipated by dimensional arguments the "bigger
things are bigger in all measures" perspective detailed
theoretical expectations are complicated by baryon evolu-
tion uncertainties. Even with some baryon model prescribed,
the stochastic nature of the halo evolution in a hierarchical
clustering framework will impose variance about the mean
behavior, the scale of which is likely to be sensitive to the
Improved understanding of cluster scaling relations is
desirable on both astrophysical and cosmological grounds.
Better astrophysical models of galaxy and hot gas evo-
lution in halos will improve constraints on cosmological
parameters obtained from studies of cluster samples (e.g.
Vikhlinin et al. 2006; Rozo et al. 2007; Mantz et al. 2007).
The relation between X-ray luminosity Lx and halo
mass M is a diagnostic of the halo baryon fraction and the
entropy structure of the intracluster gas. From X-ray data
alone, constraints on the Lx M relation have been obtained
using either direct or statistical arguments. The direct ap-
proach assumes that the intracluster gas is in hydrostatic
Work supported in part by US Department of Energy contract DE-AC02-76SF00515
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Rykoff, E.S.; Evrard, A.E.; McKay, T.A.; Becker, M.R.; Johnston, D.E.; Koester, B.P. et al. The L_X-M relation of Clusters of Galaxies, report, May 16, 2008; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc899887/m1/1/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.