Massive galaxies in cosmological simulations : UV - selected sample at redshift z = 2

We study the properties of galaxies at redshift z = 2 in a Λ cold dark matter (ΛCDM) universe, using two different types of hydrodynamic simulation methods (Eulerian TVD and SPH) and a spectrophotometric analysis in the Un, G,R filter set. The simulated galaxies at z = 2 satisfy the color-selection criteria proposed by Adelberger et al. (2004) and Steidel et al. (2004) when we assume Calzetti extinction with E(B− V ) = 0.15. We find that the number density of simulated galaxies brighter than R < 25.5 at z = 2 is about 5 × 10 h Mpc, roughly one order of magnitude larger than that of Lyman break galaxies at z = 3. The most massive galaxies at z = 2 have stellar masses & 10M⊙, and their observed-frame G− R colors lie in the range 0.0 < G− R < 1.0. They typically have been continuously forming stars with a rate exceeding 30 M⊙ yr −1 over a few Gyrs from z = 10 to z = 2, although the TVD simulation indicates a more sporadic star formation history than the SPH simulations. Of order half of their stellar mass was already assembled by z ∼ 4. The bluest galaxies with colors −0.2 < G−R < 0.0 at z = 2 are somewhat less massive, withMstar < 10 hM⊙, and lack a prominent old stellar population. On the other hand, the reddest massive galaxies at z = 2 with G − R ≥ 1.0 and Mstar > 10 hM⊙ finished the build-up of their stellar mass by z ∼ 3. Interestingly, our study suggests that the majority of the most massive galaxies at z = 2 should be detectable at Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A. Email: [email protected] Princeton University Observatory, Princeton, NJ 08544, U.S.A. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3, OHA, UK Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85740 Garching bei München, Germany