UV LUMINOSITY FUNCTIONS AT REDSHIFTS z∼ 4 TO z∼ 10: 10,000 GALAXIES FROM HST LEGACY FIELDS

Abstract

The remarkable Hubble Space Telescope(HST) data sets from the CANDELS, HUDF09, HUDF12, ERS, and BoRG/HIPPIES programs have allowed us to map the evolution of the rest-frame UV luminosity function (LF) from z 10 to z 4. We develop new color criteria that more optimally utilize the full wavelength coverage from the optical, near-IR, and mid-IR observations over our search fields, while simultaneously minimizing the incompleteness and eliminating redshift gaps.We have identified 5859, 3001, 857, 481, 217, and 6 galaxy candidates at z 4, z 5, z 6, z 7, z 8, and z 10, respectively, from the ∼1000 arcmin 2 area covered by these data sets.This sample of >10,000 galaxy candidates at ⩾ z 4 is by far the largest assembled to date with HST.The selection of z 4-8 candidates over the five CANDELS fields allows us to assess the cosmic variance; the largest variations are at ⩾ z 7. Our new LF determinations at z 4 and z 5 span a 6 mag baseline and reach to -16 AB mag.These determinations agree well with previous estimates, but the larger samples and volumes probed here result in a more reliable sampling of >L* galaxies and allow us to reassess the form of the UV LFs.Our new LF results strengthen our earlier findings to s 3.4 significance for a steeper faint-end slope of the UV LF at > z 4, with α evolving from a = -  1.64 0.04 at z 4 to a = -  2.06 0.13 at z 7 (and a = -  2.02 0.23 at z 8), consistent with that expected from the evolution of the halo mass function.We find less evolution in the characteristic magnitude M * from z 7 to z 4; the observed evolution in the LF is now largely represented by changes in f*.No evidence for a non-Schechter-like form to the z ∼ 4-8 LFs is found.A simple conditional LF model based on halo growth and evolution in the M/L ratio µ + - z ( ( 1) ) 1.5 of halos provides a good representation of the observed evolution.