DAWN Cake Talk - Jens-Kristian Krogager

Molecular hydrogen in the early universe and why we need massive spectroscopic surveys

Molecular hydrogen is a very important tracer of regions of active star formation in the universe. Despite the very faint emissivity of H2, we can readily observe this elusive molecule in absorption towards bright sources such as young stars in our galaxy or towards distant quasars or gamma-ray bursts. However, the single absorption sightlines can be challenging to interpret and we therefore need large statistical samples.

In this talk, I will show some brand new results from the recently commissioned 4MOST spectroscopic survey instrument in Chile. We have discovered a molecular absorption system at z = 4.1 with the highest molecular fraction ever seen beyond the local group. This system implies a much higher incidence of molecular gas than what was expected at such early times.

I will end the talk by showcasing the proposed Widefield Spectroscopic Telescope, led by Roland Bacon in Lyon, for the next ESO flagship telescope. The WST will be a dedicated spectroscopic survey facility unlike anything seen before, and will enable ground-breaking spectroscopic transients in the optical range.