Constraints on the Star-Forming Interstellar Medium in Galaxies Back to the First Billion Years of Cosmic Time

TL;DR

This paper reviews the progress in understanding the molecular gas content of high-redshift galaxies, highlighting recent observational advances and the potential of new interferometers to study galaxy evolution in the early universe.

Contribution

It summarizes recent observational achievements and discusses how upcoming instruments will enable systematic studies of molecular gas in early galaxies.

Findings

Detection of CO emission in over 100 high-redshift galaxies.

Advances in gravitational lensing techniques for gas mass measurement.

Potential of EVLA and ALMA to revolutionize high-redshift galaxy studies.

Abstract

Constraints on the molecular gas content of galaxies at high redshift are crucial to further our understanding of star formation and galaxy evolution through cosmic times, as molecular gas is the fuel for star formation. Since its initial detection at large cosmic distances almost two decades ago, studies of molecular gas in the early universe have come a long way. We have detected CO emission from >100 galaxies, covering a range of galaxy populations at z>1, reaching out to z>6, down to sub-kpc scale resolution, and spanning ~2 orders of magnitude in gas mass (aided by gravitational lensing). Recently, it has even become possible to directly identify distant galaxies through their molecular emission lines without prior knowledge of their redshifts. The new generation of powerful long wavelength interferometers such as the Expanded Very Large Array (EVLA) and Atacama Large (sub)Millimeter Array (ALMA) thus hold the promise to liberate studies of molecular gas in high redshift galaxies from their heavy pre-selection. This will enable more systematic studies of the molecular gas content in star-forming galaxies back to the earliest cosmic times.