Examining transitional galaxies to understand the role of clusters and their dynamical status in galaxy quenching

Abstract

ABSTRACT In this work, we consider four different galaxy populations and two distinct global environments in the local Universe (z ≤ 0.11) to investigate the evolution of transitional galaxies (such as star-forming spheroids and passive discs) across different environments. Our sample is composed of 3899 galaxies within the R200 radius of 231 clusters and 11 460 field galaxies. We also investigate the impact of the cluster’s dynamic state, as well as the galaxy’s location in the projected phase space diagram. We found that although the cluster environment as a whole influences galaxy evolution, the cluster dynamical state does not. Furthermore, star-forming galaxies represent recent cluster arrivals in comparison to passive galaxies (especially in the case of early-types). Among the early-type galaxies, we find that the Dn(4000) and H δ parameters indicate a smooth transition between the subpopulations. In particular, for the star-forming early-type galaxies, we detect a significant difference between field and cluster galaxies, as a function of stellar mass, for objects with log M*/M⊙ > 10.5. Analysing the colour gradient, the results point towards a picture where field galaxies are more likely to follow the monolithic scenario, while the cluster galaxies the hierarchical scenario. In particular, if we split the early-type galaxies into lenticulars and ellipticals, we find that the steeper colour gradients are more common for the lenticulars. Finally, our results indicate the need for galaxy pre-processing in smaller groups, before entering clusters.