2017ApJ...843...36S

We present the first determination of the galaxy luminosity function (LF) at z ∼ 4, 5, 6, and 7, in the rest-frame optical at λ_rest∼900 nm (z' band). The rest-frame optical light traces the content in low-mass evolved stars (∼stellar mass-M_*), minimizing potential measurement biases for M_*. Moreover, it is less affected by nebular line emission contamination and dust attenuation, is independent of stellar population models, and can be probed up to z ∼ 8 through Spitzer/IRAC. Our analysis leverages the unique full-depth Spitzer/IRAC 3.6-8.0 µm data over the CANDELS/GOODS-N, CANDELS/GOODS-S, and COSMOS/UltraVISTA fields. We find that, at absolute magnitudes where M_z^′^ is fainter than -23 mag, M_z^′^ linearly correlates with M_UV,1600. At brighter M_z^′^, M_UV,1600 presents a turnover, suggesting that the stellar mass-to-light ratio M_*/L_UV,1600 could be characterized by a very broad range of values at high stellar masses. Median-stacking analyses recover an M_*/L_z^′^ roughly independent on M_z^′^ for M_z^′^ -23 mag, but exponentially increasing at brighter magnitudes. We find that the evolution of the LF marginally prefers a pure luminosity evolution over a pure density evolution, with the characteristic luminosity decreasing by a factor of ∼5×between z ∼ 4 and z ∼ 7. Direct application of the recovered M_*/L_z^′^ generates stellar mass functions consistent with average measurements from the literature. Measurements of the stellar-to-halo mass ratio at fixed cumulative number density show that it is roughly constant with redshift for M_h 10¹²M_☉. This is also supported by the fact that the evolution of the LF at 4 z 7 can be accounted for by a rigid displacement in luminosity, corresponding to the evolution of the halo mass from abundance matching.