The Physical and Photometric Properties of High-Redshift Galaxies in Cosmological Hydrodynamic Simulations

Abstract

We study the physical and photometric properties of galaxies at z=4 in cosmological hydrodynamic simulations of a ΛCDM universe. We focus on galaxies satisfying the ``B dropout'' criteria of the Great Observatories Origins DEEP Survey (GOODS). Our simulations predict that high-redshift galaxies show strong correlations in star formation rate (SFR) versus stellar mass, and weaker correlations versus environment and age, such that B dropouts are predicted to be the most massive, most rapidly star-forming galaxies at z=4, living preferentially in dense regions. The simulated rest-frame UV luminosity function (LF) and integrated luminosity density are in broad agreement with observations at z~4. The predicted faint-end slope is intrinsically steep but becomes shallower and is in reasonable agreement with data once GOODS selection criteria are imposed. At the bright end, there may be a modest excess of bright, rapidly star-forming galaxies. The predicted rest-frame optical LF is approximately 1 mag brighter than the rest-frame UV LF. We predict that GOODS B dropouts represent less than 50% of the total stellar mass density formed in galaxies more massive than log(M_*/M_solar)>8.7 by z=4, mainly because of brightness limits in the HST ACS bands. Most of these results are somewhat sensitive to the effects of dust extinction. On average, simulated B dropouts are less metal enriched than observed low-redshift galaxies of similar stellar mass by ~0.6 dex. Two simulated B dropouts exhibit SFRs exceeding 1000 M_solar yr^-1, similar to observed submillimeter galaxies. These galaxies are quite massive but are not undergoing starbursts; their SFRs only mildly exceed (by ~2-3 times) the SFRs that would be expected for their stellar mass. Finally, the overall distribution of dust reddening and mean stellar age may be constrained from color-color plots although the specific value for each galaxy cannot.