The Subaru FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at z 1.4

We measure the redshift-space correlation function from a spectroscopic sample of 2783 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers a redshift range of 1.19 < z < 1.55, is the first cosmological study at such high redshifts. We detect clear anisotropy due to redshift-space distortions (RSD) both in the correlation function as a function of separations parallel and perpendicular to the line of sight and its quadrupole moment. RSD has been extensively used to test general relativity on cosmological scales at z < 1. Adopting a CDM cosmology with the fixed expansion history and no velocity dispersion (v = 0), and using the RSD measurements on scales above 8 h1 Mpc, we obtain the first constraint on the growth rate at the redshift, f (z)8(z) = 0.482 ± 0.116 at z 1.4 after marginalizing over the galaxy bias parameter b(z)8(z). This corresponds to 4.2 detection of RSD. Our constraint is consistent with the prediction of general relativity f8 0.392 within the 1 confidence level. When we allow v to vary and marginalize over it, the growth rate constraint becomes f 8 = 0.494+0.126 0.120. We also demonstrate that by combining with the low-z constraints on f8, high-z galaxy surveys like the FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.