COSMOLOGICAL CONSTRAINTS FROM SUNYAEV–ZEL'DOVICH-SELECTED CLUSTERS WITH X-RAY OBSERVATIONS IN THE FIRST 178 deg2 OF THE SOUTH POLE TELESCOPE SURVEY

B A Benson,R Armstrong,J Ruel,L Knox,J Song,R J Foley,M Joy,D Luong-Van,S S Meyer,L E Bleem,L Shaw,T Plagge,T M Crawford,N W Halverson,G Bazin,A Saro,R Keisler,A Zenteno,B R Saliwanchik,E M George,M Brodwin,J D Vieira,Z Staniszewski,S Desai,A Rest,T De Haan,F W High,J Liu,J Mehl,T E Montroy,J D Hrubes,H M Cho,E Shirokoff,O Zahn,C L Chang,M Lueker,C W Stubbs,M Bayliss,J P Dudley,K Vanderlinde,A T Lee,K A Aird,G P Holder,J J Mohr,C Pryke,K K Schaffer,W L Holzapfel,J E Carlstrom,J T Sayre,S Padin,A A Stark,T Natoli,M D Gladders,A T Crites,A Clocchiatti,J E Ruhl,A Van Engelen,A Vikhlinin,B Stalder,S Hoover,C Jones,M L N Ashby,E M Leitch,A R Williamson ,W Forman ,L M Mocanu ,K T Story ,Anthony H Gonzalez ,Karl Andersson ,N L Harrington ,Jeff Mcmahon ,Christian Reichardt ,M Dobbs ,M W Bautz ,Stephen S Murray ,Daniel P Marrone ,Michael Mcdonald ,R Šuhada ,H Spieler ,Adam Mantz

doi:10.1088/0004-637x/763/2/147

Abstract

We use measurements from the South Pole Telescope (SPT) Sunyaev–Zel'dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg2 of the 2500 deg2 SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM-Newton. Assuming a spatially flat ΛCDM cosmological model, we find the SPT cluster sample constrains σ8(Ωm/0.25)0.30 = 0.785 ± 0.037. In combination with measurements of the cosmic microwave background (CMB) power spectrum from the SPT and the seven-year Wilkinson Microwave Anisotropy Probe data, the SPT cluster sample constrains σ8 = 0.795 ± 0.016 and Ωm = 0.255 ± 0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the ΛCDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (Σmν), the effective number of relativistic species (Neff), and a primordial non-Gaussianity (fNL). We find that adding the SPT cluster data significantly improves the constraints on w and Σmν beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w = −0.973 ± 0.063 and the sum of neutrino masses Σmν < 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. Assuming a ΛCDM model with a free Neff and Σmν, we measure Neff = 3.91 ± 0.42 and constrain Σmν < 0.63 eV at 95% confidence. We also use the SPT cluster sample to constrain fNL = −220 ± 317, consistent with zero primordial non-Gaussianity. Finally, we discuss the current systematic limitations due to the cluster mass calibration, and future improvements for the recently completed 2500 deg2 SPT-SZ survey. The survey has detected ∼500 clusters with a median redshift of ∼0.5 and a median mass of ∼2.3 × 1014 M☉ h−1 and, when combined with an improved cluster mass calibration and existing external cosmological data sets will significantly improve constraints on w.

Highlights

Clusters of galaxies are the most massive collapsed objects in the universe
We find that the SPTCL+H0+big bang nucleosynthesis (BBN) constraints are well approximated as σ8(Ωm/0.25)0.30 = 0.785 ± 0.037, which we show in Figure 1 by the solid and dashed lines
We have described and implemented a method that simultaneously fits for cosmological parameters and the scaling of the SZ and X-ray observables with cluster mass

Summary

Introduction

Clusters of galaxies are the most massive collapsed objects in the universe Their abundance is sensitive to multiple cosmological parameters, in particular the matter density, the amplitude of the matter power spectrum, and the dark energy equation of state (e.g., Wang & Steinhardt 1998; Haiman et al 2001; Holder et al 2001). Measurements of the cluster abundance that extend to higher redshifts become sensitive to dark energy through its effect on the growth of structure. Measurements of the cluster abundance using optical, X-ray, and SZ selection methods have been used to place competitive constraints on cosmology and dark energy parameters (e.g., Vikhlinin et al 2009b; Mantz et al 2010c; Rozo et al 2010; Vanderlinde et al 2010; Sehgal et al 2010). X-ray observables, the gas mass and inferred pressure, tend to correlate with cluster mass with low scatter, independent of the dynamical state of the cluster or the details of non-gravitational physics in clusters (e.g., Kravtsov et al 2006)

Results

Discussion

Conclusion