ABSTRACT. We have measured the rest-frame λ ~ 1500 Å comoving specific luminosity density of star-forming galaxies at redshift 3.5 < z < 6.5 (Lyman break galaxies [LBGs]) selected from deep, multiband images taken with the Hubble Space Telescope and the Advanced Camera for Surveys, obtained as part of the Great Observatories Origins Deep Survey (GOODS). The samples cover ~0.09 deg² and are also relatively deep, reaching between 0.2L and 0.5L, depending on the redshift, where L is the characteristic UV luminosity of LBGs at z ~ 3. The specific luminosity density appears to be nearly constant with redshift over the range 3 < z < 6, although the measure at z ~ 6 remains relatively uncertain, because it depends on the accurate estimate of the faint counts of the z ~ 6 sample. If LBGs are fair tracers of the cosmic star formation activity, our results suggest that at z ~ 6, namely, at less than ~7% of the current cosmic age, the universe was already producing stars as vigorously as it did near its maximum several gigayears later, at 1 z 3.

Subject headings: cosmology: observations; galaxies: distances and redshifts; galaxies: evolution; galaxies: formation

^* Based on observations obtained with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.

Print publication: Issue 2 (2004 January 10)
Received 2003 May 24, accepted for publication 2003 November 1
Published 2004 January 9