Cosmology from HI galaxy surveys with the SKA

arXiv:2607.00827 · astro-ph.CO · Submitted 2026-07-01 · Read on arXiv

Ainulnabilah Nasirudin, Philip Bull, Ziad Sakr, Joël Mayor, Benedict Bahr-Kalus, Hengxing Pan, Stefano Camera, José Fonseca, Liantsoa F. Randrianjanahary, Gabriella De Lucia, Marta Spinelli

astro-ph.CO

Submitted: 2026-07-01

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Nasirudin01

Code: https://github.com/philbull/RadioFisher

License: http://creativecommons.org/licenses/by-nc-sa/4.0/

The gist: The 21cm line from neutral hydrogen is expected to be a ubiquitous (albeit faint) tracer of galaxies in the late Universe.

Terminology

Abstract

The 21cm line from neutral hydrogen is expected to be a ubiquitous (albeit faint) tracer of galaxies in the late Universe. With SKAO-MID, large wide-field surveys of several million HI-containing galaxies will become feasible, resulting in catalogues of sufficient size to measure large-scale structure observables such as baryon acoustic oscillations and redshift-space distortions. While optical galaxy surveys over comparable areas are generally deeper, radio surveys of this kind have a number of other advantages, such as broader sampling of the halo mass function and the possibility of measuring luminosity distances via the Tully-Fisher relation. In this chapter, we provide predictions for the galaxy number counts versus redshift that will be achievable with a wide-field HI galaxy survey on SKAO-MID, along with corresponding forecasts for cosmological observables. Given the substantial uncertainty in the HI mass function with redshift, we bracket our predictions using a handful of different modelling methods.

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