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The HectoMAP survey provides a complete, mass-limited sample of 30,231 quiescent galaxies withi-band Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) imaging that spans the redshift range 0.2 <z< 0.6. We combine half-light radii based on HSC SSP imaging with redshifts andD_n4000 to explore the size–mass relation,$R_e=A\times M_{*}^{\alpha }$, and its evolution for the entire HectoMAP quiescent population and for two subsets of the data. Newcomers with 1.5 <D_n4000 < 1.6 at each redshift show a steeper increase inAas the universe ages than the population that descends from galaxies that are already quiescent at the survey limit,z∼ 0.6 (the resident population). In broad agreement with previous studies, evolution in the size–mass relation both for the entire HectoMAP sample and for the resident population (but not for the newcomers alone) is consistent with minor merger driven growth. For the resident population, the evolution in the size–mass relation is independent of the population age atz∼ 0.6. The contrast between the sample of newcomers and the resident population provides insight into the role of commonly termed “progenitor bias” on the evolution of the size–mass relation.

Abstract We use IllustrisTNG simulations to explore the dynamic scaling relation between massive clusters and their—central—brightest cluster galaxies (BCGs). The IllustrisTNG-300 simulation we use includes 280 massive clusters from the z = 0 snapshot with M 200 > 10 14 M ⊙ , enabling a robust statistical analysis. We derive the line-of-sight velocity dispersion of the stellar particles of the BCGs ( σ *,BCG ), analogous to the observed BCG stellar velocity dispersion. We also compute the subhalo velocity dispersion to measure the cluster velocity dispersion ( σ cl ). Both σ *,BCG and σ cl are proportional to the cluster halo mass, but the slopes differ slightly. Thus, like the observed relation, σ *,BCG / σ cl declines as a function of σ cl , but the scatter is large. We explore the redshift evolution of the σ *,BCG − σ cl scaling relation for z ≲ 1 in a way that can be compared directly with observations. The scaling relation has a similar slope at high redshift, but the scatter increases because of the large scatter in σ *,BCG . The simulations imply that high-redshift BCGs are dynamically more complex than their low-redshift counterparts.