Effects of cosmological model assumptions on galaxy redshift survey measurements

TL;DR

This paper examines how assumptions about the cosmological model influence the interpretation of galaxy redshift survey data, especially regarding dark energy and structure growth, highlighting the importance of model choices in future surveys.

Contribution

It demonstrates the impact of cosmological assumptions on parameter constraints and suggests that assuming a FRW space-time simplifies the analysis of deviations from the standard model.

Findings

Model assumptions significantly alter constraint results.

FRW assumption reduces coupling effects.

Different deviation scenarios affect measurements differently.

Abstract

The clustering of galaxies observed in future redshift surveys will provide a wealth of cosmological information. Matching the signal at different redshifts constrains the dark energy driving the acceleration of the expansion of the Universe. In tandem with these geometrical constraints, redshift-space distortions (RSD) depend on the build up of large-scale structure. As pointed out by many authors measurements of these effects are intrinsically coupled. We investigate this link, and argue that it strongly depends on the cosmological assumptions adopted when analysing data. Using representative assumptions for the parameters of the Euclid survey in order to provide a baseline future experiment, we show how the derived constraints change due to different model assumptions. We argue that even the assumption of a Friedman-Robertson-Walker (FRW) space-time is sufficient to reduce the importance of the coupling to a significant degree. Taking this idea further, we consider how the data would actually be analysed and argue that we should not expect to be able to simultaneously constrain multiple deviations from the standard $\Lambda$CDM model. We therefore consider different possible ways in which the Universe could deviate from the $\Lambda$CDM model, and show how the coupling between geometrical constraints and structure growth affects the measurement of such deviations.