The extended Baryon Oscillation Spectroscopic Survey (eBOSS): testing a new approach to measure the evolution of the structure growth

TL;DR

This paper introduces a new method for analyzing large redshift surveys like eBOSS to accurately measure the evolution of cosmic structure growth, avoiding biases caused by traditional averaging techniques.

Contribution

The authors develop and validate an optimal weighting method to extract differential cosmological information from eBOSS-like mock catalogues, improving over previous approaches.

Findings

The estimator provides unbiased constraints on structure growth.

The method effectively captures evolution across large redshift ranges.

It avoids signal loss associated with narrow redshift binning or averaging over evolution.

Abstract

The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is one of the first of a new generation of galaxy redshift surveys that will cover a large range in redshift with sufficient resolution to measure the baryon acoustic oscillations (BAO) signal. For surveys covering a large redshift range we can no longer ignore cosmological evolution, meaning that either the redshift shells analysed have to be significantly narrower than the survey, or we have to allow for the averaging over evolving quantities. Both of these have the potential to remove signal: analysing small volumes increases the size of the Fourier window function, reducing the large-scale information, while averaging over evolving quantities can, if not performed carefully, remove differential information. It will be important to measure cosmological evolution from these surveys to explore and discriminate between models. We apply a method to optimally extract this differential information to mock catalogues designed to mimic the eBOSS quasar sample. By applying a set of weights to extract redshift space distortion measurements as a function of redshift, we demonstrate an analysis that does not invoke the problems discussed above. We show that our estimator gives unbiased constraints.