Origins of ultradiffuse galaxies in the Coma cluster - I. Constraints from velocity phase space

Abstract

We use Keck/DEIMOS spectroscopy to confirm the cluster membership of 16 ultradiffuse galaxies (UDGs) in the Coma cluster, bringing the total number of spectroscopically confirmed UDGs from the Yagi et al. (Y16) catalogue to 25. We also identify a new cluster background UDG, confirming that most (similar to 95 per cent) of the UDGs in the Y16 catalogue belong to the Coma cluster. In this pilot study of Coma UDGs in velocity phase space, we find evidence of a diverse origin for Coma cluster UDGs, similar to normal dwarf galaxies. Some UDGs in our sample are consistent with being late infalls into the cluster environment, while some may have been in the cluster for >= 8 Gyr. The late infallen UDGs have higher absolute relative line-of-sight velocities, bluer optical colours, and within the projected cluster core, are smaller in size, compared to the early infalls. The early infall UDGs, which may also have formed in situ, have been in the cluster environment for as long as the most luminous galaxies in the Coma cluster, and they may be failed galaxies that experienced star formation quenching at earlier epochs.