Simulating Redshift-Space Distortions for Galaxy Pairs with Wide Angular Separation

TL;DR

This paper develops a new method to analyze wide-angle redshift-space distortions in galaxy surveys, improving the accuracy of RSD measurements crucial for testing gravity theories on large scales.

Contribution

It introduces a novel procedure for analyzing wide-angle effects in RSD within numerical simulations, enhancing the understanding of these effects beyond previous approximations.

Findings

Wide-angle effects are significant even at small angles.

The new method effectively separates and fits wide-angle RSD effects.

Analysis aids future large-scale galaxy survey data interpretation.

Abstract

The analysis of Redshift-Space Distortions (RSD) within galaxy surveys provides constraints on the amplitude of peculiar velocities induced by structure growth, thereby allowing tests of General Relativity on extremely large scales. The next generation of galaxy redshift surveys, such as the Baryon Oscillation Spectroscopic Survey (BOSS), and the Euclid experiment will survey galaxies out to z=2, over 10,000--20,000 sq deg. In such surveys, galaxy pairs with large comoving separation will preferentially have a wide angular separation. In standard plane-parallel theory the displacements of galaxy positions due to RSD are assumed to be parallel for all galaxies, but this assumption will break down for wide-angle pairs. Szapudi 2004 and Papai & Szapudi 2008 provided a methodology, based on tripolar spherical harmonics expansion, for computing the redshift-space correlation function for all angular galaxy pair separations. In this paper we introduce a new procedure for analysing wide-angle effects in numerical simulations. We are able to separate, demonstrate, and fit each of the effects described by the wide-angle RSD theory. Our analysis highlights some of the nuances of dealing with wide-angle pairs, and shows that the effects are not negligible even for relatively small angles. This analysis will help to ensure the full exploitation of future surveys for RSD measurements, which are currently confined to pair separations less than \sim80 Mpc/h out to z\simeq 0.5.