The abundance of Lyman-(\alpha) emitters in hierarchical models
  We present predictions for the abundance of Ly-$\alpha$ emitters in
hierarchical structure formation models. We use the {\tt GALFORM}
semi-analytical model to explore the impact on the predicted counts of varying
assumptions about the escape fraction of Ly-$\alpha$ photons, the redshift at
which the universe reionised and the cosmological density parameter. A model
with a fixed escape fraction gives a remarkably good match to the observed
counts over a wide redshift interval. We present predictions for the expected
counts in a typical observation with the Multi Unit Spectroscopic Explorer
instrument proposed for the Very Large Telescope.
