The Abundance of Low-luminosity Lyman Α Emitters at High Redshift

We derive the luminosity function of high-redshift Lyman α 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 9 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 Lyman α, in most cases via further spectroscopic observations. The selection function we constructed for our survey takes into account our varying intrinsic Lyman α line sensitivity as a function of wavelength and sky position. By virtue of the strong magnification factor, we provide constraints on the Lyman α luminosity function to unprecedented limits of 10 erg s, corresponding to a star-formation rate of 0.01 M⊙ yr . Our cumulative z ≃ 5 Lyman α luminosity function is consistent with a power law form, n(> L) ∝ L over 10 to 10 erg s. 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. Subject headings: galaxies: formation, evolution, high-redshift, luminosity function—cosmology: observations—gravitational lensing