14 June 2010

Peter Laursen

PhD thesis: Interpreting Lyman α radiation from young, dusty galaxies

Supervisor: Anja C. Andersen & Jesper Sommer-Larsen

Abstract: The significance of the Lyα emission line as a probe of the high-redshift Universe has long been established. Originating mainly in the vicinity of young, massive stars and in association with accretion of large bulks of matter, it is ideal for detecting young galaxies, the fundamental building blocks of our Universe. Since many different processes shape the spectrum and the spatial distribution of the Lyα photons in various ways, a multitude of physical properties of galaxies can be unveiled.

However, this also makes the interpretation of Lyα observations notoriously difficult. Because Lyα is a resonant line, it scatters on neutral hydrogen, having its path length from the source to our telescopes vastly increased, and taking it through regions of unknown physical conditions.

In this work, a numerical code capable of calculating realistically the radiative transfer of Lyα is presented. The code is capable of performing the radiative transfer in an arbitrary and adaptively refined distribution of Lyα source emission, temperature and velocity field of the interstellar and intergalactic medium, as well as density of neutral and ionized hydrogen, and, particularly important, dust.

Accordingly, it is applied to galaxies simulated at high resolution, yielding a number of novel and interesting results, most notably the escape fractions of Lyα photons, the effect of dust on the line profile, and the impact of the transfer through the intergalactic medium.

Furthermore, the remarkable detection of Lyα emission from a so-called "damped Lyα absorber" — a special type of objects thought to be the progenitor of present-day's galaxies — is presented, and the potential of the code for interpreting observations is demonstrated.