# Tracing HI Beyond the Local Universe

## TL;DR

This paper reviews key cosmological formulas for tracing HI emission at high redshifts with the SKA, and introduces an online calculator to aid in observation planning and analysis.

## Contribution

It provides a summary of important relations for high-redshift HI studies and offers a new online tool for researchers in the SKA era.

## Key findings

- Key formulas for high-redshift HI emission are summarized.
- An online calculator for observation planning is introduced.
- The tool facilitates accurate analysis beyond low-redshift approximations.

## Abstract

The SKA and its pathfinders will enable studies of HI emission at higher redshifts than ever before. In moving beyond the local Universe, this will require the use of cosmologically appropriate formulae that have traditionally been simplified to their low-redshift approximations. In this paper, we summarise some of the most important relations for tracing HI emission in the SKA era, and present an online calculator to assist in the planning and analysis of observations (hifi.icrar.org).