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We study the star-formation activity in a sample of ∼ 56 000 brightest cluster galaxies (BCGs) at 0.05 < z < 0.42 using optical and infra-red data from SDSS and WISE. We estimate stellar masses and star-formation rates (SFR) through SED fitting and study the evolution of the SFR with redshift as well as the effects of BCG stellar mass, cluster halo mass, and cooling time on star formation. Our BCGs have SFR = 1.4 × 10−3 − 275.2 [ |$\rm M_{\odot }$| yr−1] and sSFR = 5 × 10−15 − 6 × 10−10 [yr−1]. We find that star-forming BCGs are more abundant at higher redshifts and have higher SFR than at lower redshifts. The fraction of star-forming BCGs (f SF) varies from 30 per cent to 80 per cent at 0.05 < z < 0.42. Despite the large values of f SF, we show that only 13 per cent of the BCGs lie on the star-forming main sequence for field galaxies at the same redshifts. We also find that f SF depends only weakly on |$M_{\rm 200}$|⁠ , while it sharply decreases with |$M_{*}$|⁠. We finally find that the SFR in BCGs decreases with increasing |$t_{\rm cool}$|⁠ , suggesting that star formation is related to the cooling of the intracluster medium. However, we also find a weak correlation of |$M_{*}$| and |$M_{\rm 200}$| with |$t_{\rm cool}$| suggesting that AGNs are heating the intracluster gas around the BCGs. We compare our estimates of SFR with the predictions from empirical models for the evolution of the SFR with redshift, finding that the transition from a merger dominated to a cooling-dominated star formation may happen at z < 0.6. [ABSTRACT FROM AUTHOR]

We propose a phylogenetic approach (PA) as a novel and robust tool to detect galaxy populations (GPs) based on their chemical composition. The branches of the tree are interpreted as different GPs and the length between nodes as the internal chemical variation along a branch. We apply the PA using 30 abundance indices from the Sloan Digital Sky Survey to 475 galaxies in the Coma Cluster and 438 galaxies in the field. We find that a dense environment, such as Coma, shows several GPs, which indicates that the environment is promoting galaxy evolution. Each population shares common properties that can be identified in colour–magnitude space, in addition to minor structures inside the red sequence. The field is more homogeneous, presenting one main GP. We also apply a principal component analysis (PCA) to both samples, and find that the PCA does not have the same power in identifying GPs. [ABSTRACT FROM AUTHOR]

We present a study of the evolution of brightest cluster galaxies (BCGs) in a sample of clusters at 0.05 ≤ z < 0.35 from the Sloan Digital Sky Survey and Wide Infrared Survey Explorer with halo masses in the range |$6 \times 10^{13}\, \mathrm{M}_\odot$| (massive groups)– |$10^{15.5}\, \mathrm{M}_\odot$| (Coma-like clusters). We analyse optical and infrared colours and stellar masses of BCGs as a function of the mass of their host haloes. We find that BCGs are mostly red and quiescent galaxies and that a minority (∼9 per cent) of them are star-forming. We find that the optical g − r colours are consistent with those of red sequence galaxies at the same redshifts; however, we detect the presence of a tail of blue and mostly star-forming BCGs preferentially located in low-mass clusters and groups. Although the blue tail is dominated by star-forming galaxies, we find that star-forming BCGs may also have red g − r colours, indicating dust-enshrouded star formation. The fraction of star-forming BCGs increases with redshift and decreases with cluster mass and BCG stellar mass. We find that cool-core clusters host both star-forming and quiescent BCGs; however, non-cool-core clusters are dominated by quiescent BCGs. Star formation appears thus as the result of processes that depend on stellar mass, cluster mass, and cooling state of the intra-cluster medium. Our results suggest no significant stellar mass growth at z < 0.35, supporting the notion that BCGs had accreted most of their mass by z  = 0.35. Overall we find a low (1 per cent) active galactic nuclei fraction detected at IR wavelengths. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of galaxy colours in two galaxy clusters at $z$ ∼ 0.4, MACS J0416.1 − 2403 and MACS J1206.2 − 0847, drawn from the CLASH-VLT survey, to investigate the role of pre-processing in the quenching of star formation. We estimate the fractions of red and blue galaxies within the main cluster and the detected substructures and study the trends of the colour fractions as a function of the projected distance from the cluster and substructure centres. Our results show that the colours of cluster and substructure members have consistent spatial distributions. In particular, the colour fractions of galaxies inside substructures follow the same spatial trends observed in the main clusters. Additionally, we find that at large cluster-centric distances (r ≥ r200) the fraction of blue galaxies in both the main clusters and in the substructures is always lower than the average fraction of UVJ-selected star-forming galaxies in the field as measured in the COSMOS/UltraVista data set. We finally estimate environmental quenching efficiencies in the clusters and in the substructures and find that at large distances from the cluster centres, the quenching efficiency of substructures becomes comparable to the quenching efficiency of clusters. Our results suggest that pre-processing plays a significant role in the formation and evolution of passive galaxies in clusters at low redshifts. [ABSTRACT FROM AUTHOR]

The study of galaxy morphology is fundamental to understand the physical processes driving the structural evolution of galaxies. It has long been known that dense environments host high fractions of early-type galaxies and low fractions of late-type galaxies, indicating that the environment affects the structural evolution of galaxies. In this paper, we present an analysis of the morphological composition of red sequence galaxies in a sample of nine galaxy clusters at 0.8

We analyse the evolution of the red sequence in a sample of galaxy clusters at redshifts 0.8 < z < 1.5 taken from the HAWK-I Cluster Survey (HCS). The comparison with the low-redshift (0.04 < z < 0.08) sample of the WIde-field Nearby Galaxy-cluster Survey (WINGS) and other literature results shows that the slope and intrinsic scatter of the cluster red sequence have undergone little evolution since z = 1.5. We find that the luminous-to-faint ratio and the slope of the faint end of the luminosity distribution of the HCS red sequence are consistent with those measured in WINGS, implying that there is no deficit of red galaxies at magnitudes fainter than M*VM at high redshifts. We find that the most massive HCS clusters host a population of bright red sequence galaxies at MV < -22.0 mag, which are not observed in low-mass clusters. Interestingly, we also note the presence of a population of very bright (MV < -23.0 mag) and massive (log (M*/M⊙) > 11.5) red sequence galaxies in the WINGS clusters, which do not include only the brightest cluster galaxies and which are not present in the HCS clusters, suggesting that they formed at epochs later than z = 0.8. The comparison with the luminosity distribution of a sample of passive red sequence galaxies drawn from the COSMOS/UltraVISTA field in the photometric redshift range 0.8 < zphot < 1.5 shows that the red sequence in clusters is more developed at the faint end, suggesting that halo mass plays an important role in setting the time-scales for the build-up of the red sequence. [ABSTRACT FROM AUTHOR]