[Normal Galaxies, Clusters of Galaxies -- Oral ]

Constraints on Cosmology and X-ray Scaling Relations from the Growth of Massive Galaxy Clusters

Adam Mantz, Stanford/SLAC
Steve Allen(1), David Rapetti(1), Harald Ebeling(2), Alex Drlica-Wagner(1); (1) Stanford/SLAC, (2) University of Hawaii

I will present simultaneous constraints on galaxy cluster X-ray scaling relations and cosmology obtained from observations of the growth of massive clusters. The data set consists of 238 flux-selected clusters at redshifts $z \leq 0.5$ drawn from the ROSAT All-Sky Survey, and incorporates extensive Chandra follow-up observations. Our results on the scaling relations are consistent with excess heating of the intracluster medium; however, this heating appears to be limited to the central regions of clusters. The evolution of the scaling relations is consistent with the predictions of simple gravitational collapse models, indicating that the effects of excess heating on cluster properties do not evolve significantly within redshift 0.5. Clusters with cooling cores make up a significant fraction of our sample at all redshifts, consistent with most previous observations and with recent simulations. For spatially flat, constant-$w$ cosmological models, the cluster data yield $\Omega_m = 0.23 \pm 0.04$, $\sigma_8 = 0.82 \pm 0.05$, and $w = -1.01 \pm 0.20$, including conservative allowances for systematic uncertainties. Our results are consistent and competitive with a variety of independent cosmological data. In evolving-$w$ models, marginalizing over transition redshifts in the range 0.05--1, the combination of the growth of structure data with the cosmic microwave background, supernovae, cluster gas mass fractions and baryon acoustic oscillations constrains the dark energy equation of state at late and early times to be respectively $w_0 = -0.88 \pm 0.21$ and $w_{et} = -1.05 \^{+0.20}_{-0.36}$. While our results on dark energy from the growth of structure alone are statistically limited at present, constraints from the combination with other cosmological data could be tightened by incorporating gravitational lensing observations and/or improved simulations of baryonic physics in clusters.