Dwarf Galaxies and Cluster Environments

We report an investigation of the dwarf galaxies (M-r < -15) inside 26 clusters at z= 0.15-0.25, using optical images taken with Subaru Suprime-Cam and the X-ray data from the Chandra. Our goal is to help understand the relationship between the dwarf and giant galaxies, and the dwarfs and their host clusters, to eventually address a question of the co-evolution of galaxies and their environments. When we examine dwarf-to-giant ratios as a function of cluster density or X-ray luminosity, we find no variation in the ratios. We also find that: (1) the investigation of the dwarf galaxy density distribution is very sensitive to the background galaxies and the colour of galaxies; (2) underestimating the background galaxy counts tends to mimic a 'flat' distribution of dwarf galaxies over cluster-centric distance; (3) approximately 40-60 per cent of faint galaxies remain undetected by the detection algorithm near the centre of clusters, even after carefully treating the diffuse light by nearby bright galaxies; (4) dwarf galaxies extend up to 2 Mpc from the centre in most clusters. The blue dwarf galaxies (more than 0.3 bluer than cluster red sequence V - I colour) extend to larger cluster-centric radii compared to the red dwarf galaxies; (5) the major contribution to the difference in the radial distribution comes from the colour, rather than the size, of galaxies; (6) relative to the NFW profile, all of the galaxy populations are showing a deficit near the cluster core (r < 0.3 Mpc). The deviation is the most significant for blue dwarf galaxies.