The formation history of massive cluster galaxies as revealed by CARLA

摘要: We use a sample of 37 the densest clusters and protoclusters across 1.3 ≤ z 3.2 from Clusters Around Radio-Loud AGN (CARLA) survey to study formation massive cluster galaxies. optical i′-band infrared 3.6 4.5 μm images statistically select sources within these measure their median observed colours; 〈i′ − [3.6]〉. find abundance galaxies increases with decreasing redshift, suggesting objects may form an evolutionary sequence, lower redshift in having similar properties descendants high-redshift protoclusters. that protocluster have approximately unevolving observed-frame i′ [3.6] colour examined range. compare evolution [3.6]〉 simplistic galaxy models. Taking full population into account, we show stars majority occurs over at least 2 Gyr, peaks ∼ 2–3. From colours, cannot determine star histories individual galaxies, but must been rapidly terminated produce red colours. Finally, > assembled 0.5 Gyr them forming significant fraction stars. This means few could formed via dry mergers.