HI Simulations for Cosmology with the SKA Observatory

arXiv:2606.25969 · astro-ph.CO · Submitted 2026-06-24 · Read on arXiv

Tommaso Ronconi, Gabriella De Lucia, Marta Spinelli, Pascal Hitz, Fabio Fontanot, Francesco Sinigaglia, Lizhi Xie, Robert M. Yates, José Luis Bernal, Anna Bonaldi, Stefano Camera, Isabella P. Carucci, Steven Cunnington, Francisco-Shu Kitaura, Joël Mayor, Rajesh Mondal, Giulia Piccirilli, Digvijay Wadekar

astro-ph.CO

Submitted: 2026-06-24

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Ronconi01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes

Code: https://github.com/rajeshmondal18/N-body

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

The gist: We present a comparative overview of state-of-the-art methods for modelling the distribution of neutral hydrogen (HI) in the post-reionization Universe, developed in preparation for upcoming SKAO

Terminology

Abstract

We present a comparative overview of state-of-the-art methods for modelling the distribution of neutral hydrogen (HI) in the post-reionization Universe, developed in preparation for upcoming SKAO cosmological surveys. Our aim is to assess how different physical and empirical assumptions reflect into predictions for key observables such as the cosmic HI density, the HI mass function, and the HI-halo mass relation. We consider both: (i) semi-analytical approaches that self-consistently evolve baryonic components within dark matter merger trees through physically motivated prescriptions and (ii) empirical schemes tailored to different observables and based on fast approximations designed for large ensemble studies. By comparing the predictions from the different methods considered, we find overall consistency in integrated quantities such as HI, yet systematic differences in the detailed shape and scatter of the HI--halo mass relation and its redshift evolution. Semi-analytical models offer physically grounded predictions but depend on assumed prescriptions, while empirical methods provide flexibility and computational efficiency at the expense of robustness in extrapolated regions of the parameter space. The increasing number of HI measurements from SKA precursors and pathfinders (including surveys with MeerKAT, ASKAP, and FAST) will provide critical observational constraints to refine and calibrate current simulation methodologies. In turn, increasingly realistic HI simulations play a key role in interpreting these data, guiding survey design and analysis strategies, in preparation for the advent of SKAO data.

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