The rest-frame optical (900nm) galaxy luminosity function at z∼4–7: abundance matching points to limited evolution in the MSTAR/MHALO ratio at z ≥ 4

Abstract

We present the first determination of the galaxy luminosity function (LF) at z ∼4, 5, 6, and 7, in the rest-frame optical at l ~ 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 Mz¢ is fainter than ≳-23 mag, Mz¢ linearly correlates with MUV,1600. At brighter Mz¢, MUV,1600 presents a turnover, suggesting that the stellar mass-to-light ratioM* LUV,1600 could be characterized by a very broad range of values at high stellar masses. Median-stacking analyses recover an M* Lz¢ roughly independent on Mz¢ for Mz¢ ≳ -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 ~5x between z∼4 and z ∼7. Direct application of the recovered M* Lz¢ 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 forMh ≳ 1012 M⊙ 12 . 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.