Cosmological performance of SKA HI galaxy surveys

TL;DR

This paper evaluates the cosmological capabilities of the SKA HI galaxy surveys, demonstrating that SKA2's billion galaxy survey will significantly enhance dark energy measurements compared to existing surveys.

Contribution

It provides an improved model for HI galaxy counts and bias, and forecasts the survey's potential for precise dark energy measurements using SKA configurations.

Findings

SKA2's billion galaxy survey will outperform current surveys in dark energy constraints.

The improved model predicts high galaxy yields for various SKA phases.

Forecasts show significant reduction in errors on BAO measurements.

Abstract

The Square Kilometre Array (SKA) will conduct the biggest spectroscopic galaxy survey ever, by detecting the 21cm emission line of neutral hydrogen (HI) from around a billion galaxies over 3/4 of the sky, out to a redshift of z~2. This will allow the redshift-space matter power spectrum, and corresponding dark energy observables, to be measured with unprecedented precision. In this paper, we present an improved model of the HI galaxy number counts and bias from semi-analytic simulations, and use it to calculate the expected yield of HI galaxies from surveys with a variety of Phase 1 and 2 SKA configurations. We illustrate the relative performance of the different surveys by forecasting errors on the radial and transverse scales of the baryon acoustic oscillation (BAO) feature, finding that the full "billion galaxy survey" with SKA2 will deliver the largest dark energy figure of merit of any current or future large-scale structure survey.