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

Kavli Affiliate: Naoyuki Tamura

| First 5 Authors: Teppei Okumura, Chiaki Hikage, Tomonori Totani, Motonari Tonegawa, Hiroyuki Okada

| Summary:

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 the redshift ranges 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 LCDM
cosmology with the fixed expansion history and no velocity dispersion
$sigma_{rm v}=0$, and using the RSD measurements on scales above 8Mpc/h, we
obtain the first constraint on the growth rate at the redshift,
$f(z)sigma_8(z)=0.482pm 0.116$ at $zsim 1.4$ after marginalizing over the
galaxy bias parameter $b(z)sigma_8(z)$. This corresponds to $4.2sigma$
detection of RSD. Our constraint is consistent with the prediction of general
relativity $fsigma_8sim 0.392$ within the $1-sigma$ confidence level. When
we allow $sigma_{rm v}$ to vary and marginalize it over, the growth rate
constraint becomes $fsigma_8=0.494^{+0.126}_{-0.120}$. We also demonstrate
that by combining with the low-z constraints on $fsigma_8$, high-z galaxy
surveys like the FastSound can be useful to distinguish modified gravity models
without relying on CMB anisotropy experiments.

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