  The Large Area Lyman Alpha survey has found ~ 150 Lyman-alpha emitters at
z=4.5. While stellar models predict a maximum Lyman-alpha equivalent width (EW)
of 240 angstrom, 60% of the Lyman-alpha emitters have EWs exceeding this value.
We attempt to model the observed EW distribution by combining stellar
population models with an extrapolation of Lyman break galaxy luminosity
function at z=4, incorporating observational selection effects and Malmquist
bias. To reproduce the high EWs seen in the sample we need to postulate a
stellar initial mass function (IMF) with extreme slope alpha = 0.5 (instead of
2.35); zero metallicity stars; or narrow-lined active galactic nuclei. The
models also reveal that only 7.5-15% of galaxies need show Lyman-alpha emission
to explain the observed number counts. This raises the possibility that either
star-formation in high redshift galaxies is episodic or the Lyman-alpha
galaxies we are seeing are the youngest 7.5-15% and that Lyman-alpha is
strongly quenched by dust at about 10 Mega-years of age.
