Molecular hydrogen in absorption at high redshifts. Science cases for CUBES

TL;DR

This paper discusses the potential of the upcoming CUBES spectrograph to advance high-redshift molecular hydrogen observations, enabling detailed studies of cold gas in galaxies and outflows.

Contribution

It outlines science cases for CUBES, emphasizing its role in studying high-redshift H₂ absorption and the physical conditions of cold gas in the universe.

Findings

Recent progress in H₂ detection at high redshift.

CUBES will enhance efficiency of follow-up spectroscopy.

Potential to study cold gas in galaxies and AGN outflows.

Abstract

Absorption lines from molecular hydrogen ($\rm H_2$) in the spectra of background sources are a powerful probe of the physical conditions in intervening cold neutral medium. At high redshift, $z>2$, $\rm H_2$ lines are conveniently shifted in the optical domain, allowing the use of ground-based telescopes to perform high-resolution spectroscopy, which is essential for a proper analysis of the cold gas. We describe recent observational progress, based on the development of efficient pre-selection techniques in low-resolution spectroscopic surveys such as the Sloan Digital Sky Survey (SDSS). The next generation of spectrographs with high blue-throughput, such as CUBES, will certainly significantly boost the efficiency and outcome of follow-up observations. In this paper, we discuss high priority science cases for CUBES, building on recent $\rm H_2$ observations at high-z: probing the physical conditions in the cold phase of regular galaxies and outflowing gas from active galactic nucleus.