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

Abstract 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 &amp;lt; z &amp;lt; 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 &amp;lt; 1. Adopting a ΛCDM cosmology with the fixed expansion history and no velocity dispersion (σv = 0), and using the RSD measurements on scales above 8 h−1 Mpc, we obtain the first constraint on the growth rate at the redshift, f (z)σ8(z) = 0.482 ± 0.116 at z ∼ 1.4 after marginalizing over the galaxy bias parameter b(z)σ8(z). This corresponds to 4.2 σ detection of RSD. Our constraint is consistent with the prediction of general relativity fσ8 ∼ 0.392 within the 1 σ confidence level. When we allow σv to vary and marginalize over it, the growth rate constraint becomes $f\sigma _8=0.494^{+0.126}_{-0.120}$. We also demonstrate that by combining with the low-z constraints on fσ8, high-z galaxy surveys like the FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.