Multiwavelength investigations of co-evolution of bright cluster galaxies and their host clusters

We report a systematic multiwavelength investigation of environments of the brightest cluster galaxies (BCGs), using the X-ray data from the Chandra archive, and optical images taken with 34 × 27 arcmin2 field-of-view Subaru Suprime-Cam. Our goal is to help understand the relationship between the BCGs and their host clusters, and between the BCGs and other galaxies, to eventually address a question of the formation and co-evolution of BCGs and the clusters. Our results include the following. (1) Morphological variety of BCGs, or the second or the third brightest galaxy (BCG2, BCG3), is comparable to that of other bright red sequence galaxies, suggesting that we have a continuous variation of morphology between BCGs, BCG2, and BCG3, rather than a sharp separation between the BCG and the rest of the bright galaxies. (2) The offset of the BCG position relative to the cluster centre is correlated to the degree of concentration of cluster X-ray morphology (Spearman ρ = -0.79), consistent with an interpretation that BCGs tend to be off-centred inside dynamically unsettled clusters. (3) Morphologically disturbed clusters tend to harbour the brighter BCGs, implying that the 'early collapse' may not be the only major mechanism to control the BCG formation and evolution.