The Abundance of Low‐Luminosity Lyα Emitters at High Redshift

We derive the luminosity function of high-redshift Lyα-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 Lyα, in most cases via further spectroscopic observations. The selection function we constructed for our survey takes into account our varying intrinsic Lyα line sensitivity as a function of wavelength and sky position. By virtue of the strong magnification factor, we provide constraints on the Lyα luminosity function to unprecedented limits of 1040 ergs s -1, corresponding to a star formation rate of 0.01 M☉ yr-1. Our cumulative z ≃ 5 Lyα luminosity function is consistent with a power-law form n(>L) ∝ L-1 over 1041-1042.5 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.