HETDEX: Evolution of Lyman Alpha Emitters

The Hobby Eberly Telescope Dark Energy Experiment (HETDEX) will produce a sample of 800,000 Lyman Alpha Emitters (LAEs) over the 1.9<z<3.5 range. This epoch marks a peak in star formation activity over the whole universe, and is therefore of prime importance to understand the assembly of galaxies. The HETDEX LAE sample will allow us to probe the evolution of these young star-forming systems with unprecedented detail. We present results from the HETDEX Pilot Survey, conducted with the prototype instrument VIRUS-P, regarding the redshift evolution of different physical properties of LAEs, including their number density, dust content, and Lyman Alpha photon escape fraction. Our results show a strong evolution in the Lyman Alpha escape fraction with redshift, most likely associated with the buildup of dust in the ISM. Dust is shown to be the main parameter setting the escape of Lyman Alpha photons. The observed relation between E(B-V) and the escape fraction indicates that radiative transfer effects in LAEs promote the escape of Lyman Alpha photons, but only up to the point of them suffering similar amounts of extinction as continuum photons. Enhancement of the Lyman Alpha EW (e.g. due to the presence of a clumpy medium) seems not to be a common process in these objects. We also discuss the potential of the full HETDEX sample to study the evolution of LAE properties.