The rest-frame optical (900nm) galaxy luminosity function at z ~ 4-7: abundance matching points to limited evolution in the M_(STAR)/M_(HALO) 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 λ_(res) ~ 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 _5x 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 ≳ 10^(12) M⊙. 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.

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