Blind Wide Area Surveys: Where will we find redshifted atomic and molecular absorption?

TL;DR

This paper discusses the potential of future wide-area radio surveys to discover redshifted atomic and molecular absorption systems, which are crucial for understanding the early Universe's gas content and fundamental physics.

Contribution

It analyzes current detection challenges and highlights how next-generation radio telescopes will improve the discovery rate through advanced bandwidth and field-of-view capabilities.

Findings

Current detections are very rare, with only 80 in HI 21-cm and five in other species.

Next-generation telescopes will significantly increase detection prospects.

Selection criteria are key to identifying promising absorption systems.

Abstract

Spectroscopy of redshifted radio absorption of atomic and molecular species provide excellent probes of the cold component of the gas in the early Universe which can be used to address many important issues, such as measuring baryonic content, probing large-scale structure and galaxy evolution, as well as obtaining independent measurements of various combinations of fundamental constants at large look-back times. However, such systems are currently very rare with only 80 detected in HI 21-cm and five in OH and millimetre-band species. Here we summarise the main selection criteria responsible for this and how the next generation of radio telescopes are expected to circumvent these through their wide instantaneous bandwidths and fields-of-view.