# Blind Search for 21-cm Absorption Systems in New Generation Chinese Radio Telescopes

## TL;DR

This paper forecasts the potential of new Chinese radio telescopes, FAST and Tianlai, to conduct blind searches for 21-cm absorption systems, significantly advancing our understanding of neutral hydrogen in the universe.

## Contribution

It presents a forecast of the capabilities of FAST and Tianlai telescopes for discovering 21-cm absorption systems, highlighting their potential to vastly increase known systems.

## Key findings

- Over a thousand 21-cm absorption systems could be discovered in a few years.
- FAST's high sensitivity enables detection of faint absorption signals.
- Tianlai's wide field of view allows extensive sky coverage.

## Abstract

Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation Chinese radio telescopes through a blind searching of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China -- Five-hundred-meter Aperture Spherical radio Telescope (FAST) and Tianlai 21-cm cosmology experiment (Tianlai). Facilitated by either the high sensitivity (FAST) or the wide field of view (Tianlai) of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.