The ultraviolet luminosity density of the universe from photometric redshifts of galaxies in the Hubble Deep Field

Studies of the Hubble Deep Field (HDF) and other deep surveys have revealed an apparent peak in the ultraviolet (UV) luminosity density, and therefore the star formation rate density, of the universe at redshifts 1 < z < 2. W e use photometric redshifts of galaxies in the HDF to determine the comovin g UV luminosity density, and we find that, when errors tin particular, samp ling error) are properly accounted for, a flat distribution is statisticall y indistinguishable from a distribution peaked at z similar or equal to 1.5 . Furthermore, we examine the effects of cosmological surface brightness (S B) dimming on these measurements by applying a uniform SE cut to all galaxy fluxes after correcting them to redshift z = 5. We find that, when compari ng all galaxies at the same intrinsic surface brightness sensitivity, the U V luminosity density contributed by high intrinsic SE regions increases by almost 2 orders of magnitude from z similar or equal to 0 to z similar or e qual to 5. This suggests that there exists a population of objects with ver y high star formation rates at high redshifts that apparently do not exist at low redshifts. The peak of star formation, then, likely occurs somewhere beyond z > 2.