The VIMOS Public Extragalactic Redshift Survey (VIPERS): Gravity test from the combination of redshift-space distortions and galaxy-galaxy lensing at 0.5 < z < 1.2

Description

We carry out a joint analysis of redshift-space distortions and galaxy-galaxy lensing, with the aim of measuring the growth rate of structure; this is a key quantity for understanding the nature of gravity on cosmological scales and late-Time cosmic acceleration. We make use of the final VIPERS redshift survey dataset, which maps a portion of the Universe at a redshift of z 0.8, and the lensing data from the CFHTLenS survey over the same area of the sky. We build a consistent theoretical model that combines non-linear galaxy biasing and redshift-space distortion models, and confront it with observations. The two probes are combined in a Bayesian maximum likelihood analysis to determine the growth rate of structure at two redshifts z = 0.6 and z = 0.86. We obtain measurements of fσ8(0.6) = 0.48 ± 0.12 and fσ8(0.86) = 0.48 ± 0.10. The additional galaxy-galaxy lensing constraint alleviates galaxy bias and σ8degeneracies, providing direct measurements of f and σ8: [f(0.6),σ8(0.6)] = [0.93 ± 0.22,0.52 ± 0.06] and [f(0.86),σ8(0.86)] = [0.99 ± 0.19,0.48 ± 0.04]. These measurements are statistically consistent with a Universe where the gravitational interactions can be described by General Relativity, although they are not yet accurate enough to rule out some commonly considered alternatives. Finally, as a complementary test we measure the gravitational slip parameter, EG, for the first time at z > 0.6. We find values of EG(0.6) = 0.16±0.09 and EG(0.86) = 0.09±0.07, when EGis averaged over scales above 3 h-1Mpc. We find that our EGmeasurements exhibit slightly lower values than expected for standard relativistic gravity in a ΛCDM background, although the results are consistent within 1-2σ.

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