Cross-correlation cosmography with HI intensity mapping

TL;DR

This paper explores using HI intensity mapping combined with optical surveys to perform cross-correlation cosmography, aiming to measure dark energy parameters with high precision, especially with SKA data.

Contribution

It demonstrates the potential of HI intensity mapping in cross-correlation cosmography to constrain dark energy, highlighting advantages like redshift resolution and high-redshift leverage.

Findings

Dark energy equation of state constrained to ~8% with SKA-optical surveys

HI intensity mapping offers excellent redshift resolution for lensing measurements

CMB as a second source plane is less competitive than galaxy surveys

Abstract

The cross-correlation of a foreground density field with two different background convergence fields can be used to measure cosmographic distance ratios and constrain dark energy parameters. We investigate the possibility of performing such measurements using a combination of optical galaxy surveys and HI intensity mapping surveys, with emphasis on the performance of the planned Square Kilometre Array (SKA). Using HI intensity mapping to probe the foreground density tracer field and/or the background source fields has the advantage of excellent redshift resolution and a longer lever arm achieved by using the lensing signal from high redshift background sources. Our results show that, for our best SKA-optical configuration of surveys, a constant equation of state for dark energy can be constrained to $\simeq 8\%$ for a sky coverage $f_{\rm sky}=0.5$ and assuming a $\sigma(\Omega_{\rm DE})=0.03$ prior for the dark energy density parameter. We also show that using the CMB as the second source plane is not competitive, even when considering a COrE-like satellite.