∼ 4 and the Evolution of the Uv Luminosity Density at High Redshift Hubble Fellow

We present initial results of a survey for star-forming galaxies in the redshift range 3.8 < ∼ z < ∼ 4.5. This sample consists of a photometric catalog of 244 galaxies culled from a total solid angle of 0.23 square degrees to an apparent magnitude of IAB = 25.0. Spectroscopic redshifts in the range 3.61 ≤ z ≤ 4.81 have been obtained for 48 of these galaxies; their median redshift is 〈z〉 = 4.13. Selecting these galaxies in a manner entirely analogous to our large survey for Lyman break galaxies at smaller redshift (2.7 < ∼ z < ∼ 3.4) allows a relatively clean differential comparison between the populations and integrated luminosity density at these two cosmic epochs. Over the same range of UV luminosity, the spectroscopic properties of the galaxy samples at z ∼ 4 and z ∼ 3 are indistinguishable, as are the luminosity function shapes and the total integrated UV luminosity densities (ρUV (z = 3)/ρUV (z = 4) = 1.1 ± 0.3). We see no evidence at these bright magnitudes for the steep decline in the star formation density inferred from fainter photometric Lyman-break galaxies in the Hubble Deep Field (HDF). Based on data obtained at the Palomar Observatory, the Cerro–Tololo Inter-American Observatory, the William Herschel Telescope, and the W.M. Keck Observatory. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was was made possible by the generous financial support of the W.M. Keck Foundation. NSF Young Investigator