New determinations of the UV luminosity functions from z ~ 9 to 2 show a remarkable consistency with halo growth and a constant star formation efficiency

Here we provide the most comprehensive determinations of the rest-frame UV luminosity function (LF) available to date with the Hubble Space Telescope (HST) at z ~ 2-9. Essentially all of the noncluster extragalactic legacy fields are utilized, including the Hubble Ultra Deep Field, the Hubble Frontier Fields parallel fields, and all five CANDELS fields, for a total survey area of 1136 arcmin2. Our determinations include galaxies at z ~ 2-3 leveraging the deep HDUV, UVUDF, and ERS WFC3/UVIS observations available over an ~150 arcmin2 area in the GOODS-North and GOODS-South regions. All together, our collective samples include >24,000 sources, >2.3 larger than previous selections with HST. We identify 5766, 6332, 7240, 3449, 1066, 601, 246, and 33 sources at z ~ 2, 3, 4, 5, 6, 7, 8, and 9, respectively. Combining our results with an earlier z ~ 10 LF determination by Oesch et al., we quantify the evolution of the UV LF. Our results indicate that there is (1) a smooth flattening of the faint-end slope a from a ~ -2.4 at z ~ 10 to a ~ -1.5 at z ~ 2, (2) minimal evolution in the characteristic luminosity M* at z = 2.5, and (3) a monotonic increase in the normalization from z ~ 10 to 2, which can be well described by a simple second-order polynomial, consistent with an "accelerated"evolution scenario. We find that each of these trends (from z ~ 10 to 2.5 at least) can be readily explained on the basis of the evolution of the halo mass function and a simple constant star formation efficiency model.