The abundance of low-luminosity Lyα emitters at high redshift

We derive the luminosity function of high-redshift Lyalpha-emitting sources from a deep, blind, spectroscopic survey that utilized strong-lensing magnification by intermediate-redshift clusters of galaxies. We observed carefully selected regions near nine clusters, consistent with magnification factors generally greater than 10 for the redshift range 4.5 < z < 6.7. Eleven emission-line candidates were located in the range 2: 2 < z < 5: 6 whose identification we justify as Lyalpha, in most cases via further spectroscopic observations. The selection function we constructed for our survey takes into account our varying intrinsic Lyalpha line sensitivity as a function of wavelength and sky position. By virtue of the strong magnification factor, we provide constraints on the Lyalpha luminosity function to unprecedented limits of 10(40) ergs s(-1), corresponding to a star formation rate of 0.01 M-circle dot yr(-1). Our cumulative z similar or equal to 5 Lyalpha luminosity function is consistent with a power-law form n(>L) proportional to L-1 over 10(41)-10(42.5) ergs s(-1). When combined with the results of other surveys, limited at higher luminosities, our results suggest evidence for the suppression of star formation in low-mass halos, as predicted in popular models of galaxy formation.