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

TL;DR

This study measures the galaxy luminosity function at z~4-7 in the rest-frame optical, revealing limited evolution in the stellar-to-halo mass ratio and supporting a model of luminosity evolution driven by halo mass growth.

Contribution

First determination of the rest-frame optical galaxy luminosity function at z~4-7, linking it to halo mass evolution and stellar mass-to-light ratios.

Findings

Luminosity function shows a characteristic luminosity decrease by ~5x from z~4 to 7.

Stellar-to-halo mass ratio remains roughly constant for halos >10^12Msun across these redshifts.

Luminosity evolution better explains the data than density evolution.

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 lambda_rest~900 nm (z' band). The rest-frame optical light traces the content in low-mass evolved stars (~stellar mass - Mstar), minimizing potential measurement biases for Mstar. 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 3.6um-to-8.0um data over the CANDELS/GOODS-N, CANDELS/GOODS-S and COSMOS/UltraVISTA fields. We find that at absolute magnitudes M_z' 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 Mstar/L_UV,1600 could be characterised by a very broad range of values at high stellar masses. Median-stacking analysis recovers a Mstar/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 evolution in luminosity over a pure evolution in density, with the characteristic luminosity decreasing by a factor ~5x between z~4 and z~7. Direct application of the recovered Mstar/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 Mh>10^12Msun. 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.