The high-mass end of the red sequence at z ˜ 0.55 from SDSS-III/BOSS: completeness, bimodality and luminosity function

We have developed an analytical method based on forward-modellingtechniques to characterize the high-mass end of the red sequence (RS)galaxy population at redshift z ˜ 0.55, from the DR10 BOSS (BaryonOscillation Spectroscopic Survey) CMASS spectroscopic sample, whichcomprises ˜600 000 galaxies. The method, which follows an unbinnedmaximum likelihood approach, allows the deconvolution of the intrinsicCMASS colour-colour-magnitude distributions from photometric errors andselection effects. This procedure requires modelling the covariancematrix for the i-band magnitude, g - r colour and r - i colour usingStripe 82 multi-epoch data. Our results indicate that theerror-deconvolved intrinsic RS distribution is consistent, within thephotometric uncertainties, with a single point (0.05 mag) in thecolour-colour plane at fixed magnitude, for a narrow redshift slice. Wehave computed the high-mass end (^0.55M_i ≲-22) of the ^0.55i-band RS luminosity function (RS LF) inseveral redshift slices within the redshift range 0.52 z 0.63.In this narrow redshift range, the evolution of the RS LF is consistent,within the uncertainties in the modelling, with a passively evolvingmodel with Φ_* = (7.248 ± 0.204) × 10^-4 Mpc^-3 mag^-1, fading at a rate of 1.5± 0.4 mag per unit redshift. We report RS completeness as afunction of magnitude and redshift in the CMASS sample, which willfacilitate a variety of galaxy-evolution and clustering studies usingBOSS. Our forward-modelling method lays the foundations for futurestudies using other dark-energy surveys like the Extended BaryonOscillation Spectroscopic Survey or the Dark Energy SpectroscopicInstrument, which are affected by the same type of photometricblurring/selection effects.