Galaxy and Mass Assembly (GAMA): Redshift Space Distortions from the Clipped Galaxy Field

TL;DR

This paper introduces a novel clipping technique on galaxy density fields from the GAMA survey, reducing nonlinear effects and enabling more accurate cosmological measurements of structure growth without reliance on simulations.

Contribution

It develops a theoretical model for the power spectrum of a clipped galaxy field in redshift space, extending the applicability of traditional models significantly.

Findings

Clipping extends the Kaiser model's validity by over three times in wavenumber.

Measured the growth rate fσ8(z=0.18) as 0.29 ± 0.10.

Reduced nonlinear effects in galaxy power spectrum analysis.

Abstract

We present the first cosmological measurement derived from a galaxy density field subject to a `clipping' transformation. By enforcing an upper bound on the galaxy number density field in the Galaxy and Mass Assembly survey (GAMA), contributions from the nonlinear processes of virialisation and galaxy bias are greatly reduced. This leads to a galaxy power spectrum which is easier to model, without calibration from numerical simulations. We develop a theoretical model for the power spectrum of a clipped field in redshift space, which is exact for the case of anisotropic Gaussian fields. Clipping is found to extend the applicability of the conventional Kaiser prescription by more than a factor of three in wavenumber, or a factor of thirty in terms of the number of Fourier modes. By modelling the galaxy power spectrum on scales k < 0.3 h/Mpc and density fluctuations $\delta_g < 4$ we measure the normalised growth rate $f\sigma_8(z = 0.18) = 0.29 \pm 0.10$.