Dozens of ultra-compact dwarf galaxies detected

UCD/GCs around the brightest galaxies in the Fornax cluster.
Credit: Saifollahi et al., 2021.

Astronomers from the University of Groningen and elsewhere have identified 44 new ultra-compact dwarf galaxies (UCDs). The newly found objects most likely belong to the Fornax Cluster. The discovery is reported in a paper published March 31 on the arXiv pre-print server.

UCDs are very compact  with high stellar populations, containing about 100 million stars. They display masses, colors and metallicities between those of  and early-type dwarf galaxies. These ultra-compact stellar systems could provide important insights on the formation and evolution of galaxies in the universe.

Located some 65 million  away from the Earth, the Fornax Cluster is the second-richest  of galaxies nearby. Due to its relatively , it is a valuable source of information about galaxy clusters in general. Previous observations of Fornax Cluster have detected 61 member UCDs in total.

Now, a group of astronomers led by Teymoor Saifollahi of the University of Groningen, the Netherlands, reports the finding of dozens of new potential UCDs that may be associated with the Fornax Cluster. By analyzing the data from the Fornax Deep Survey (FDS), Vista Hemisphere Survey (VHS) and archival datasets from the Visible and Infrared Survey Telescope for Astronomy (VISTA), they identified 44 candidate UCDs in the outskirts of this cluster.

“With the deep optical images of the Fornax Deep Survey, combined with public near-infrared data, we revisit the UCD population of the Fornax cluster and search for UCD candidates, for the first time, systematically, out to the virial radius of the galaxy cluster,” the researchers wrote in the paper.

The team initially selected 220 UCD candidates, and from this broad sample, they chose 44 that have a higher probability of being real UCDs. Almost all of the newly detected UCD candidates are located outside the core of the Fornax Cluster (more than 1,170 light years away from the cluster’s center).

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