Cross correlation surveys with the Square Kilometre Array

TL;DR

This paper explores how cross-correlating different SKA data products with each other and with CMB measurements enhances cosmological parameter constraints, especially for dark energy and modified gravity, by leveraging combined information and calibration techniques.

Contribution

It demonstrates the significant benefits of cross-correlations in SKA data for improving dark energy and modified gravity constraints, including calibration of photometric redshifts.

Findings

Cross-correlations increase dark energy figure of merit.

Photometric redshifts can be calibrated with cross-correlation techniques.

Modified gravity parameters are tightly constrained through combined data.

Abstract

By the time that the first phase of the Square Kilometre Array is deployed it will be able to perform state of the art Large Scale Structure (LSS) as well as Weak Gravitational Lensing (WGL) measurements of the distribution of matter in the Universe. In this chapter we concentrate on the synergies that result from cross-correlating these different SKA data products as well as external correlation with the weak lensing measurements available from CMB missions. We show that the Dark Energy figures of merit obtained individually from WGL/LSS measurements and their independent combination is significantly increased when their full cross-correlations are taken into account. This is due to the increased knowledge of galaxy bias as a function of redshift as well as the extra information from the different cosmological dependences of the cross-correlations. We show that the cross-correlation between a spectroscopic LSS sample and a weak lensing sample with photometric redshifts can calibrate these same photometric redshifts, and their scatter, to high accuracy by modelling them as nuisance parameters and fitting them simultaneously cosmology. Finally we show that Modified Gravity parameters are greatly constrained by this cross-correlations because weak lensing and redshift space distortions (from the LSS survey) break strong degeneracies in common parameterisations of modified gravity.