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RESEARCH
The XMM Cluster Survey: testing chameleon gravity using the profiles of clusters

H. Wilcox, D. Bacon, R. C. Nichol, P. J. Rooney, A. Terukina, A. K. Romer, K. Koyama, G.-B. Zhao, R. Hood, R. Mann, M. Hilton, M. Manolopoulou, M. Sahlén, C. A. Collins, A. Liddle, J. A. Mayers, N. Mehrtens, C. J. Miller, J. P. Stott, P. T. P. Viana

Abstract
The chameleon gravity model postulates the existence of a scalar field that couples with matter to mediate a fifth force. If it exists, this fifth force would influence the hot X-ray emitting gas filling the potential wells of galaxy clusters. However, it would not influence the clusters weak lensing signal. Therefore, by comparing X-ray and weak lensing profiles, one can place upper limits on the strength of a fifth force. This technique has been attempted before using a single, nearby cluster (Coma, z = 0.02). Here we apply the technique to the stacked profiles of 58 clusters at higher redshifts (0.1 < z < 1.2), including 12 new to the literature, using X-ray data from the XMM Cluster Survey and weak lensing data from the Canada–France–Hawaii–Telescope Lensing Survey. Using a multiparameter Markov chain Monte Carlo analysis, we constrain the two chameleon gravity parameters (β and ϕ). Our fits are consistent with general relativity, not requiring a fifth force. In the special case of f(R) gravity (where $\beta =\sqrt{1/6}$ ), we set an upper limit on the background field amplitude today of |fR0| < 6 × 10−5 (95 per cent CL). This is one of the strongest constraints to date on |fR0| on cosmological scales. We hope to improve this constraint in future by extending the study to hundreds of clusters using data from the Dark Energy Survey.

Keywords
gravitation - gravitational lensing: weak - X-rays: galaxies: clusters

Monthly Notices of the Royal Astronomical Society
Volume 452, Issue 2, Page 1171
2015 September