The properties of Lyα emitting galaxies in hierarchical galaxy formation models

We present detailed predictions for the properties of Ly alpha-emitting galaxies in the framework of the Lambda cold dark matter cosmology, calculated using the semi-analytical galaxy formation model GALFORM. We explore a model that assumes a top-heavy initial mass function in starbursts and that has previously been shown to explain the sub-millimetre number counts and the luminosity function of Lyman-break galaxies at high redshift. We show that this model, with the simple assumption that a fixed fraction of Ly alpha photons escape from each galaxy, is remarkably successful at explaining the observed luminosity function of Ly alpha emitters (LAEs) over the redshift range 3 < z < 6.6. We also examine the distribution of Ly alpha equivalent widths and the broad-band continuum magnitudes of emitters, which are in good agreement with the available observations. We look more deeply into the nature of LAEs, presenting predictions for fundamental properties such as the stellar mass and radius of the emitting galaxy and the mass of the host dark matter halo. The model predicts that the clustering of LAEs at high redshifts should be strongly biased relative to the dark matter, in agreement with observational estimates. We also present predictions for the luminosity function of LAEs at z > 7, a redshift range that is starting to be be probed by near-infrared surveys and using new instruments such as the Dark Ages Z Lyman Explorer (DAzLE).