Lyman break galaxies at z = 4–6 in cosmological smoothed particle hydrodynamics simulations

Abstract

We perform a spectrophotometric analysis of galaxies at redshifts z= 4–6 in cosmological smoothed particle hydrodynamics simulations of a Λ cold dark matter universe. Our models include radiative cooling and heating by a uniform ultraviolet (UV) background, star formation, supernova feedback, and a phenomenological model for galactic winds. Analysing a series of simulations of varying box size and particle number allows us to isolate the impact of numerical resolution on our results. Specifically, we determine the luminosity functions in B, V, R, i′ and z′ filters, and compare the results with observational surveys of Lyman break galaxies (LBGs) performed with the Subaru telescope and the Hubble Space Telescope. We find that the simulated galaxies have UV colours consistent with observations and fall in the expected region of the colour—colour diagrams used by the Subaru group. The stellar masses of the most massive galaxies in our largest simulation increase their stellar mass from M★~ 1011 M⊙ at z= 6 to M★~ 1011.7 M⊙ at z= 3. Assuming a uniform extinction of E(B−V) = 0.15, we also find reasonable agreement between simulations and observations in the space density of UV bright galaxies at z= 3–6, down to the magnitude limit of each survey. For the same moderate extinction level of E(B−V) ~ 0.15, the simulated luminosity functions match observational data, but have a steep faint-end slope with α~−2.0. We discuss the implications of the steep faint-end slope found in the simulations. Our results confirm the generic conclusion from earlier numerical studies that UV bright LBGs at z≥ 3 are the most massive galaxies with E(B−V) ~ 0.15 at each epoch.