The universe as seen through Lyman alpha – characterizing the most distant galaxies by observing nearby galaxies

by Dr Jens Melinder (Stockholm University)

Friday 19 May 2017, 10:30 → 11:30 Europe/Stockholm

FC61

The Ly alpha line is widely used to identify and confirm galaxies in the distant universe, close to the epoch when the first galaxies formed and when the universe was reionized. However, the fact that Ly alpha is a resonant line makes it optically thick even at relatively low neutral hydrogen column densities. This means that the radiative transport of Ly alpha photons through galaxies is a complex problem where the structure, kinematics, dust content, and neutral hydrogen content of the interstellar medium all contribute to the process. In this talk I will give a review of the latest results from high redshift Lyman alpha surveys, and the implications of these findings on reionization and galaxy evolution. In the coming decade the James Webb Space Telescope will enable us to find Lya emitters at extremely high redshift and thereby probing the very first galaxies. However, using the line emission to identify and study these very distant galaxies requires further studies of the radiative transfer effects. On that note, I will summarize the current research on Lyman alpha emitting galaxies at low redshift, in particular the Lyman Alpha Reference Sample. This project is a major multi-wavelength imaging and spectroscopic campaign of local normal star-forming galaxies, UV-luminous starburst systems, and luminous infrared galaxies using HST and ground-based telescopes. The aim of this survey is to probe what physical conditions and processes regulate the emission of Ly alpha radiation on local and global galactic scales. The first results of the LARS survey reveal that: (i) when Ly alpha manages to escape it does so in the form of diffuse scattering halos, (ii) both dust content and geometry plays an important role in Ly alpha escape, (iii) ISM kinematics is very important to allow escape.