A census of ultra-compact dwarf galaxies in nearby galaxy clusters

TL;DR

This paper provides a comprehensive survey of ultra-compact dwarf galaxies across multiple nearby galaxy clusters, analyzing their properties, distribution, and possible origins to better understand their nature and relation to other stellar systems.

Contribution

It offers the first nearly complete census of UCDs in several galaxy clusters, revealing their heterogeneity and environmental dependence, and discusses their potential formation scenarios.

Findings

UCDs are heterogenous in properties and origins.

Their spatial distribution is intermediate between globular clusters and dwarf ellipticals.

Blue UCDs align with nuclear star clusters, red UCDs may form from merged star clusters.

Abstract

Ultra-compact dwarf galaxies (UCDs) are predominatly found in the cores of nearby galaxy clusters. Besides the Fornax and Virgo cluster, UCDs have also been confirmed in the twice as distant Hydra I and Centaurus clusters. Having (nearly) complete samples of UCDs in some of these clusters allows the study of the bulk properties with respect to the environment they are living in. Moreover, the relation of UCDs to other stellar systems in galaxy clusters, like globular clusters and dwarf ellipticals, can be investigated in detail with the present data sets. The general finding is that UCDs seem to be a heterogenous class of objects. Their spatial distribution within the clusters is in between those of globular clusters and dwarf ellipticals. In the colour-magnitude diagram, blue/metal-poor UCDs coincide with the sequence of nuclear star clusters, whereas red/metal-rich UCDs reach to higher masses and might have originated from the amalgamation of massive star cluster complexes in merger or starburst galaxies.