Two channels for the formation of compact dwarf galaxies in clusters of galaxies

We have identified two channels for the formation of compact dwarf galaxies in the Illustris simulation by reconstructing mass and distance histories of candidates located in the vicinity of the simulation's most massive cluster galaxies. One channel is tidal stripping of Milky Way-mass galaxies that form outside of clusters and eventually sink into them, spiralling in towards central massive objects. The second channel of formation is an in situ formation (in reference to the parent cluster) of dwarf mass galaxies, with negligible evolution and limited change in stellar mass. We find 19 compact dwarf galaxies at the centres of 14 clusters, consistent with observations: 30 per cent of these have an external origin while 70 per cent are formed in situ.