Abstract

In Montero-Dorta et al., we show that luminous red galaxies (LRGs) from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) at z similar to 0.55 can be divided into two groups based on their star formation histories. So-called fast-growing LRGs assemble 80 per cent of their stellar mass at z similar to 5, whereas slow-growing LRGs reach the same evolutionary state at z similar to 1.5. We further demonstrate that these two subpopulations present significantly different clustering properties on scales of similar to 1-30 Mpc. Here, we measure the mean halo mass of each subsample using the galaxy-galaxy lensing technique, in the similar to 190 deg(2) overlap of the LRG catalogue and the CS82 and CFHTLenS shear catalogues. We show that fast- and slow-growing LRGs have similar lensing profiles, which implies that they live in haloes of similar mass: log(M-halo(fast)/h(-1)M(circle dot)) = 12.85(-0.26)(+0.16) and log(M-halo(slow)/h(-1)M(circle dot)) = 12.92(-0.22)(+0.16). This result, combined with the clustering difference, suggests the existence of galaxy assembly bias, although the effect is too subtle to be definitively proven, given the errors on our current weak-lensing measurement. We show that this can soon be achieved with upcoming surveys like DES.