The Rest - Frame Uv Luminosity Function and Luminosity Density from 506 Udf , Udf - Ps , and Goods I - Dropouts

1 Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #9803. 2 Observations have been carried out using the Very Large Telescope at the ESO Paranal Observatory under Program ID(s): LP168.A-0485. ABSTRACT A very large sample of 506 i-dropouts (z ∼ 6 galaxies) have been obtained from all the deep, wide-area HST ACS fields: HUDF, GOODS (enhanced by the extensive SNe search data – to be the v2.0 GOODS release), and UDF-Parallel ACS fields (UDF-Ps). With our selection criteria, we show that the contamination levels are 8% (i.e., 92% or ∼ 465 are at z ∼ 6). This is the first comprehensive quantitative analysis of such a large sample at z ∼ 6, only 0.9 Gyr from recombination, and is used to establish optimal measures of both the luminosity function and the luminosity density at z ∼ 6, and their evolution relative to the z ∼ 3 dropouts. A total of 122 i-dropouts [(i 775 − z 850) AB > 1.3, (V 606 − z 850) AB > 2.8] are detected in the HUDF to z 850,AB ∼ 29.5 (the 8σ limit). Fits to the optical-infrared (ACS/NICMOS) colors of the HUDF dropout galaxies give mean UV slopes of β = −1.8. This is bluer than the dropout population at z ∼ 3, suggesting lower dust content at z ∼ 6. The sizes of the i-dropouts in our samples are small, with an ∼ L * galaxy having r hl ∼ 0.8 kpc or ∼ 0.14 ′′. There is clear size evolution, with a redshift dependence between z ∼ 6 and z ∼ 2.5 of (1 + z) −1.1±0.3 for fixed luminosity. Significant differences were found in the surface density of i-dropouts between the fields, as expected from cosmic variance. Great care was taken to normalize out these differences. Completeness, flux, and contamination corrections are performed in a very systematic and quantitative way for the three data sets. After establishing and performing these corrections, we combine the data to derive a rest-frame continuum UV (∼ 1350Å) luminosity function at z ∼ 6. The best-fit Schechter parameters are M * z=3), the faintest limit yet reached for galaxies at high redshifts z > 2. We find strong evidence for evolution of the luminosity function between z ∼ …