The growth of brightest cluster galaxies and intracluster light over the past 10 billion years

We constrain the evolution of the brightest cluster galaxy plus intracluster light (BCG + ICL) using an ensemble of 42 galaxy groups and clusters that span redshifts of z = 0.05−1.75 and masses of M_500,c = 2 × 10¹³−10¹⁵ M☉. Specifically, we measure the relationship between the BCG + ICL stellar mass M. and M_500,c at projected radii 10 < r < 100 kpc for three different epochs. At intermediate redshift (z¯ = 0.40), where we have the best data, we find M. ∝ M_500,c^0.48 ± ^0.06. Fixing the exponent of this power law for all redshifts, we constrain the normalization of this relation to be 2.08 ± 0.21 times higher at z¯ = 0.40 than at high redshift (z¯ = 1.55). We find no change in the relation from intermediate to low redshift (z¯ = 0.10). In other words, for fixed M₅₀₀c, M. at 10 < r < 100 kpc increases from z¯ = 1.55 to z¯ = 0.40 and not significantly thereafter. Theoretical models predict that the physical mass growth of the cluster from z = 1.5 to z = 0 within r_500,c is 1.4×, excluding evolution due to definition of r₅₀₀c. We find that M. within the central 100 kpc increases by ∼3.8× over the same period. Thus, the growth of M. in this central region is more than a factor of 2 greater than the physical mass growth of the cluster as a whole. Furthermore, the concentration of the BCG + ICL stellar mass, defined by the ratio of stellar mass within 10 kpc to the total stellar mass within 100 kpc, decreases with increasing M_500,c at all z. We interpret this result as evidence for inside–out growth of the BCG + ICL over the past 10 Gyr, with stellar mass assembly occurring at larger radii at later times.