Fredagskollokvium: Lyman-alpha observables of the high-z Universe

Lyman alpha (Lya) emission provides a unique window into the high
redshift Universe and can further our understanding of the physical
processes involved. In this talk I will discuss two particular Lya
observables: The Lya luminosity function and Lya spectra of galaxies.
First, I will present a technique to compute the Lya luminosity
function (LF) from the much better constrained UV continuum LF. This
allows us to predict the evolution of the Lya LF with cosmic time,
which can be relevant for understanding the Epoch of Reionization.
Interestingly, our model predicts a very steep faint-end slope, which
appears to have been confirmed by the most recent observations.
Secondly, I will show results from our Lya radiative transfer
calculations. In particular, I will discuss the "shell model", which
is an only six-parameter model representing a Lya emitting galaxy by a
central luminous source surrounded by an outflowing shell of hydrogen
and dust. In spite of its simplicity, the shell-model is highly
successful in reproducing observed Lya spectra. Why this model can
reproduce the complex scattering process through the multiphase
interstellar medium is still unclear. After reviewing the free
parameters of the "shell-model", I will describe common problems
arising when shell-model parameters are extracted from observed Lya
spectra. In order to overcome this, we propose a fully automated
procedure, which allows for quantification of uncertainties and
potential degeneracies.
I will conclude with a brief outlook into our future work where we
will try to combine our Lya radiative transfer code with results from
the "First Billion Years" (FiBY) hydrodynamical simulation in order to
explore the physical meaning of the "shell model" parameters.