THE EVOLUTION OF Lyα-EMITTING GALAXIES BETWEEN<i>z</i>= 2.1 AND<i>z</i>= 3.1

Abstract

We describe the results of a new, wide-field survey for z=3.1 Ly-alpha\nemission-line galaxies (LAEs) in the Extended Chandra Deep Field South\n(ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary\nbroadband photometry from the MUSYC survey, we identify a complete sample of\n141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and\nobservers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20\nAngstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is\ndominated by x-ray sources and foreground objects with GALEX detections, but\nwhen these interlopers are removed, we are still left with a sample of 130 LAE\ncandidates, 39 of which have spectroscopic confirmations. This sample overlaps\nthe set of objects found in an earlier ECDF-S survey, but due to our filter's\nredder bandpass, it also includes 68 previously uncataloged sources. We confirm\nearlier measurements of the z=3.1 LAE emission-line luminosity function, and\nshow that an apparent anti-correlation between equivalent width and continuum\nbrightness is likely due to the effect of correlated errors in our\nheteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to\nLAEs found at z=2.1. We show that in the ~1 Gyr after z~3, the LAE luminosity\nfunction evolved significantly, with L* fading by ~0.4 mag, the number density\nof sources with L &gt; 1.5E42 ergs/s declining by ~50%, and the equivalent width\nscale-length contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms.\nWhen combined with literature results, our observations demonstrate that over\nthe redshift range z~0 to z~4, LAEs contain less than ~10% of the\nstar-formation rate density of the universe.\n