Z∼ 7–10 Galaxies in the HUDF and GOODS Fields: UV Luminosity Functions

Abstract

We use all available deep optical ACS and near-IR data over both the HUDF and the two GOODS fields to search for star-forming galaxies at z≳ 7 and constrain the UV LF within the first 700 Myr. Our data set includes ~23 arcmin2 of deep NICMOS J + H data and ~248 arcmin2 of ground-based (ISAAC+MOIRCS) data, coincident with ACS optical data of greater or equal depths. In total, we find eight <z > ∼ 7.3 z-dropouts in our search fields, but no z ∼ 9 J-dropout candidates. A careful consideration of a wide variety of different contaminants suggest an overall contamination level of just ~12% for our z-dropout selection. After performing detailed simulations to accurately estimate the selection volumes, we derive constraints on the UV LFs at z ∼ 7 and z ∼ 9. For a faint-end slope α = − 1.74, our most likely values for MUV* and φ* at z ∼ 7 are –19.8 ± 0.4 mag and 1.1+ 1.7−0.7 × 10−3 Mpc−3, respectively. Our search results for z ∼ 9 J-dropouts set a 1 σ lower limit on MUV* of –19.6 mag assuming that φ* and α are the same as their values at slightly later times. This lower limit on MUV* is 1.4 mag fainter than our best-fit value at z ∼ 4, suggesting that the UV LF has undergone substantial evolution over this time period. No evolution is ruled out at 99% confidence from z ∼ 7 to z ∼ 6 and at 80% confidence from z ∼ 9 to z ∼ 7. We find that the mass-to-light ratio of halos evolves as ~(1 + z)−1 if we require that the observed brightening in MUV* with redshift [i.e., MUV* = (− 21.02 ± 0.09) + (0.36 ± 0.08) (z − 3.8) ] be consistent with the expected evolution in the halo mass function. Finally, we consider the shape of the UV LF at z≳ 5 and discuss the implications of the Schechter-like form of the observed LFs, particularly the unexpected abrupt cutoff at the bright end.