The evolution of Lyα-emitting galaxies between z = 2.1 and z = 3.1

We describe the results of a new, wide-field survey for z = 3.1 Lyα emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). By using a nearly top-hat 5010 Å filter and complementary broadband photometry from the MUSYC survey, we identify a complete sample of 141objects with monochromatic fluxes brighter than 2.4 × 10^-17ergcm^-2s ^-1 and observers-frame equivalent widths (EWs) greater than ∼80 Å (i.e., 20 Å in the rest frame of Lyα). The bright end of this data set is dominated by X-ray sources and foreground objects with Galaxy Evolution Explorer detections, but when these interlopers are removed, we are still left with a sample of 130 LAE candidates, 39 of which have spectroscopic confirmations. This sample overlaps the set of objects found in an earlier ECDF-S survey, but due to our filter's redder bandpass, it also includes 68 previously uncataloged sources. We confirm earlier measurements of the z = 3.1 LAE emission-line luminosity function and show that an apparent anticorrelation between EW and continuum brightness is likely due to the effect of correlated errors in our heteroskedastic data set. Finally, we compare the properties of z = 3.1 LAEs to LAEs found at z = 2.1. We show that in the ∼ 1 Gyr after z ∼ 3, the LAE luminosity function evolved significantly, with L* fading by 0.4mag, the number density of sources with L > 1.5 × 10 ⁴²ergs^-1 declining by 50%, and the EW scale length contracting from 70⁺⁷ _{- 5} to 50⁺⁹ _{- 6} Å. When combined with literature results, our observations demonstrate that over the redshift range z ∼ 0 to z ∼ 4, LAEs contain less than 10% of the star formation rate density of the universe.