Possible merger signatures of the bulges of non-dwarf galaxies in the core of the Coma Cluster

Abstract

In this paper, we discuss a method to study virialised clusters of galaxies with no-interaction features, like tails and bridges, using diagnostics of bulge classification and their properties, namely Sérsic index (n) and the Kormendy relation. We study a sample of non-dwarf galaxies in the core of the Coma Cluster using HST/ACS data. We divided our galaxy sample into 4 categories based on bulge to total light ratio (B/T): B/T<0.3 (12%), 0.3<B/T≤0.6 (38%), 0.6<B/T≤0.8 (29%) and B/T>0.8 (21%). We classified the galaxy bulges using Sérsic index (n) and the Kormendy relation, where classical bulges are a result of mergers and pseudo bulges are a result of secular evolution. Using Sérsic index we found that 75% galaxies in our sample had classical bulges (n>2) and 25% galaxies had pseudo-bulges (n<2). From the Kormendy diagram we found that 90% galaxies had classical and 10% galaxies had pseudo-bulges. We observed that classical bulges with B/T≥0.3 galaxies in the central region of Coma Cluster (within 0.4 Mpc from NGC 4874) are redder in colour (F475W−F814W≥1.17). Pseudo-bulges and B/T≤0.3 galaxies are within 0.6 to 1.1 Mpc from NGC 4874 and are bluer in colour (F475W−F814W≤1.13). We find that the majority of galaxies with classical bulges have B/T≥0.3 and those with pseudo-bulges have B/T≤0.3. With our study of the Kormendy relation and colour, B/T and distance from centre relations, we infer that galaxies in the central region of Coma Cluster with B/T≥0.3 may have formed by mergers and those with B/T≤0.3 may have formed by secular process.