Galaxy Properties in Clusters: Dependence on the Environment and the Cluster Identification Techniques

TL;DR

This study examines how galaxy properties vary with environment and cluster identification methods, revealing differences in galaxy sizes, types, and dynamics between cluster and field galaxies, and across different cluster catalogs.

Contribution

It compares galaxy properties in clusters identified by X-ray and optical methods, highlighting environmental effects and selection biases on galaxy evolution.

Findings

Galaxies in clusters have larger sizes than field galaxies of the same type.

X-ray and MaxBCG clusters show similar size-luminosity and Faber-Jackson relations.

X-ray selected clusters have a higher fraction of early-type galaxies.

Abstract

We investigate the dependence of several galaxy properties on the environment and cluster identification techniques. We select clusters of galaxies from two catalogues based on the SDSS: the ROSAT-SDSS Galaxy Cluster Survey, and the MaxBCG Catalogue. Based on a volume limited sample of galaxies drawn from the spectroscopic DR5 SDSS, we constructed sub-samples of clusters of galaxies with more than ten members. Scaling relations as well as segregation of galaxy properties as a function of the normalized clustocentric radii are analyzed. The properties of galaxies in clusters are compared with those of field galaxies. Galaxies in X-ray and MaxBCG selected clusters show similar size-luminosity relations. At equal luminosity, late type galaxies in the field have sizes smaller than cluster galaxies of the same morphological type. The Faber-Jackson relation for early-type galaxies in clusters is also the same for X-ray selected and MaxBCG clusters. We found clear differences between the dynamical properties of galaxies in clusters, the brightest cluster galaxies ($BCG_s$) and field galaxies. Using several criteria to classify galaxies into morphological types, we reproduce the well know morphological segregation. The correlation is up to $r/r_{200} \sim 1$. For the whole range of clustocentric distances, X-ray selected clusters present a higher fraction of early type galaxies than MaxBCG clusters. We also found that bright galaxies preferentially inhabit the cluster centers. Median sizes of galaxies, such as the radius that enclose 50% of petrosian flux $r_{50}$, present a behaviour that also depends on the cluster selection criteria. The resultsare discussed in terms of the different processes that affect the evolution of galaxies in different environments.