Star Formation History of the Hubble Ultra Deep Field: Comparison with the Hubble Deep Field–North

We use the NICMOS Treasury and ACS HUDF images to measure the extinctioncorrected star formation history for 4681 galaxies in the region common to bothimages utilizing the star formation rate distribution function and othertechniques similar to those employed with the NICMOS and WFPC2 images in theHDFN. Unlike the HDFN the NICMOS region of the HUDF appears to lack highlyluminous and high star formation rate galaxies at redshifts beyond 3. The HUDFprovides a region that is completely uncorrelated to the HDFN and thereforeprovides and independent measure of the star formation history of the universe.The combined HUDF and HDFN star formation rates show an average star formationrate of 0.2 solar masses per yer per cubic megaparsec. The average SFR of thecombined fields at z = 1-3 is 0.29 solar masses per year per cubic megaparsecwhile the average at z = 4-6 is 1.2 solar masses per year per cubic megaparsec.The SFRs at all redshifts are within 3 sigma of the average over all redshifts.Comment: Accepted for publication in the Astrophysical Journa