NEW LIMITS ON GALAXY FORMATION AT HIGH-REDSHIFT

The results from the first search for Lyalpha emission from primeval galaxies at redshifts of z greater-than-or-equal-to 7 are presented. The aim of this search is to detect Lyalpha emission from the progenitors of the general present-day galaxy population. We have undertaken deep imaging with IRCAM in the near-infrared J window (approximately 1.0-1.5 mum), using four narrow-band filters of 2 per cent FWHM. Over an area of sky of 3.0 arcmin2 we find no young galaxies to a sensitivity limit of congruent-to 10(-18) m-2. This sensitivity corresponds to star formation at redshifts of 7.2 less-than-or-equal-to z less-than-or-equal-to 9.3 of only a few times the rate observed in spiral galaxies. At least one-third of the progenitors of bright galaxies must have had Lyalpha luminosities of < 7.5 x 10(37) W (OMEGA = 1, H-0 = 50 km s-1 Mpc-1) at these redshifts. Our limits on the luminosities of young galaxies at z greater-than-or-equal-to 7 are comparable to the lower redshift limits of optical searches. By combining the upper limits in the optical and near-infrared passbands, it is now apparent that if the Lyalpha emission from young galaxies is unattenuated by dust then galaxies could not have been many times brighter than present-day galaxies at any time over a large fraction of the age of the Universe (2 less-than-or-equal-to z less-than-or-equal-to 9).