In the past two decades, systematic studies have revealed hundreds of ultra-compact dwarf galaxies (UCDs) in the nearby Universe. While similar in appearance to massive globular clusters, the detection of extended stellar envelopes, complex star formation histories, elevated mass-to-light ratio, and supermassive black holes suggest that some UCDs are remnant nuclear star clusters of tidally-stripped dwarf galaxies (dEs), or even ancient compact galaxies. However, only a few objects have been found in the transient stage of tidal stripping, and this assumed evolutionary path has never been fully traced by observations. In this talk, I will show our recent discovery of over 100 galaxies in the Virgo cluster have morphologies that are intermediate between normal, nucleated dwarf galaxies and single-component UCDs, revealing a continuum that fully maps this morphological transition, and fills the “size gap” between star clusters and galaxies. Part of the evolutionary sequence is populated by “strongly-nucleated” dEs with low luminosity stellar envelopes. The “ultra-diffuse” stellar envelopes and tidal features around several of these galaxies directly show how UCDs are forming through tidal stripping, and that this evolutionary path can include an early phase as a nucleated ultra-diffuse galaxy (UDG). These UCDs represent substantial visible fossil remnants of ancient dwarf galaxies in galaxy clusters, and more low-mass remnants probably remain to be found.
BIO
Kaixiang Wang is currently a PhD candidate at the Department of Astronomy, Peking University. His main research interest is about the evolution of dwarf galaxy in clusters environment and the origin of the most extreme galaxies, e.g. ultra-compact dwarf galaxies (UCDs) and ultra-diffuse galaxies (UDGs).
