The 2df SDSS LRG and QSO survey: Evolution of the luminosity function of luminous red galaxies to z = 0.6

We present new measurements of the luminosity function (LF) of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dF SDSS LRG and Quasar (2SLAQ) survey. We have carefully quantified, and corrected for, uncertainties in the K and evolutionary corrections, differences in the colour selection methods, and the effects of photometric errors, thus ensuring we are studying the same galaxy population in both surveys. Using a limited subset of 6326 SDSS LRGs (with 0.17 < z < 0.24) and 1725 2SLAQ LRGs (with 0.5 < z < 0.6), for which the matching colour selection is most reliable, we find no evidence for any additional evolution in the LRG LF, over this redshift range, beyond that expected from a simple passive evolution model. This lack of additional evolution is quantified using the comoving luminosity density of SDSS and 2SLAQ LRGs, brighter than M0.2r- 5 log h0.7 = -22.5, which are 2.51 ± 0.03 × 10-7L⊙ Mpc-3 and 2.44 ± 0.15 × 10-7L⊙ Mpc-3, respectively (< 10 per cent uncertainty). We compare our LFs to the COMBO-17 data and find excellent agreement over the same redshift range. Together, these surveys show no evidence for additional evolution (beyond passive) in the LF of LRGs brighter than M0.2r - 5 log h0.7 = -21 (or brighter than ∼L*). We test our SDSS and 2SLAQ LFs against a simple 'dry merger' model for the evolution of massive red galaxies and find that at least half of the LRGs at z ≃ 0.2 must already have been well assembled (with more than half their stellar mass) by z ≃ 0.6. This limit is barely consistent with recent results from semi-analytical models of galaxy evolution.