Code of Conduct
Lutz Wisotzki (AIP)
Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. The Lyman-alpha transition of atomic hydrogen is an important tracer of gas in and around galaxies, especially at high redshift where the line becomes observable from the ground. Our observations with MUSE at the ESO-VLT have revealed a huge population of faint galaxies at z>3 through their Ly-alpha emission, allowing us to obtain insights into the properties of low-mass progenitors of typical present-day galaxies. The Lyman-alpha emission regions are much more extended than the starlight from these galaxies as seen by the Hubble Space Telescope, indicating that not only the interstellar but also the circumgalactic medium radiates in Ly-alpha. At the sensitivity level provided by MUSE, a large fraction of the field of view is covered with Lya emission from redshifts 3 < z < 6. The integrated cross-section is comparable to high-column density absorption systems, suggesting that we now have detected most atomic hydrogen at these redshifts also in emission.
