Star Formation at z ~ 6: The Hubble Ultra Deep Parallel Fields


Bouwens RJ, Illingworth GD, Thompson RI, Blakeslee JP, Dickinson ME, Broadhurst TJ, Eisenstein DJ, Fan X, Franx M, Meurer G, et al. Star Formation at z ~ 6: The Hubble Ultra Deep Parallel Fields. The Astrophysical Journal Letters. 2004;606 :L25-L28.

Date Published:

May 1, 2004


We report on the i-dropouts detected in two exceptionally deep AdvancedCamera for Surveys fields (B435, V606,i775, and z850 with 10σ limits of 28.8,29.0, 28.5, and 27.8, respectively) taken in parallel with the UltraDeep Field Near-Infrared Camera and Multi-Object Spectrometerobservations. Using an i-z>1.4 cut, we find 30 i-dropouts over 21arcmin2 down to z850,AB=28.1, or 1.4 i-dropoutsarcmin-2, with significant field-to-field variation (asexpected from cosmic variance). This extends i-dropout searches some~0.9 mag further down the luminosity function than was possible in theGreat Observatories Origins Deep Survey (GOODS) fields, yielding a ~7times increase in surface density. An estimate of the size evolution forUV-bright objects is obtained by comparing the composite radial fluxprofile of the bright i-dropouts (z850,AB<27.2) withscaled versions of the Hubble Deep Field-North and -South U-dropouts.The best fit is found with a(1+z)-1.57+0.50-0.53 scaling in size(for fixed luminosity), extending lower redshift (1-2.8 innumber and (1+z)0.1 in luminosity, suggesting a rest-framecontinuum UV luminosity density at z~6 that is just0.38+0.09-0.07 times that at z~3.8. Our inclusionof the size evolution makes the present estimate lower than previous z~6estimates.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555. These observations areassociated with program 9803.