Evolution in AGN fraction above a given Lyα luminosity as a function of age of the Universe. Colour scheme is identical to Fig. 1 and refers to redshift. Different symbols mark the AGN fractions above three representative Lyα luminosities. The black lines are fits to the data, see text for explanation. A transition redshift at z ~ 2.5 (age  ~ 2.5 Gyrs) is seen in all fits independent of luminosity limit. The purple line shows the redshift transition of the fraction of ULIRGs in LAE samples as presented in Nilsson & Møller (2009).