The XMM Cluster Survey: testing chameleon gravity using the profiles of clustersH. 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. VianaAbstractThe 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 β=1/6−−−√$\beta =\sqrt{1/6}$ ), 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.Keywordsgravitation - gravitational lensing: weak - X-rays: galaxies: clustersMonthly Notices of the Royal Astronomical SocietyVolume 452, Page 1171September 2015 >> PDF>> ADS>> DOI

# Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

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