The stellar mass function and star formation rate-stellar mass relation of galaxies at z ~ 4-7

We investigate the evolution of the star formation rate-stellar mass relation (SFR-M*) and galaxy stellar mass function (GSMF) of z ~ 4-7 galaxies, using cosmological simulations run with the smoothed particle hydrodynamics code P-GADGET3(XXL). We explore the effects of different feedback prescriptions (supernova-driven galactic winds and AGN feedback), initial stellar mass functions and metal cooling. We show that our fiducial model, with strong energy-driven winds and early active galactic nuclei (AGN) feedback, is able to reproduce the observed stellar mass function obtained from Lyman-break selected samples of star-forming galaxies at redshift 6 ≤ z ≤ 7. At z ~ 4, observed estimates of the GSMF vary according to how the sample was selected. Our simulations are more consistent with recent results from K-selected samples, which provide a better proxy of stellar masses and are more complete at the high-mass end of the distribution. We find that in some cases simulated and observed SFR-M* relations are in tension, and this can lead to numerical predictions for the GSMF in excess of the GSMF observed. By combining the simulated SFR(M)* relationship with the observed star formation rate function at a given redshift, we argue that this disagreement may be the result of the uncertainty in the SFR-M_* (L_UV-M_*) conversion. Our simulations predict a population of faint galaxies not seen by current observations.