Dozens of ultra-compact dwarf galaxies detected

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 group. The discovery is reported in an article published on the arXiv preprint server on March 31st.

UCDs are very compact galaxies with a high star population and contain about 100 million stars. They display masses, colors and metallicities between those of spherical clusters and early type dwarf systems. These ultra-compact galaxies can provide important insights into the formation and evolution of galaxies in the universe.

The Fornax cluster is located about 65 million light-years from Earth and is the second richest galaxy in the area. Due to its relative proximity, it is a valuable source of information about galaxies in general. Previous observations by Fornax Cluster have detected 61 members of UCDs in total.

Now a group of astronomers led by Teymoor Saifollahi of the University of Groningen, the Netherlands, is reporting on the discovery of dozens of new potential UCDs that may be related to the Fornax Cluster. By analyzing the data from the Fornax Deep Survey (FDS), Vista Hemisphere Survey (VHS) and archive data sets of the Visible and Infrared Survey Telescope for Astronomy (VISTA), they identified 44 candidate UCDs in the suburbs of this group.

“With the deep optical images of the Fornax Deep Survey, combined with public near-infrared data, we visit the UCD population of the Fornax group and for the first time systematically search for UCD candidates up to the viral radius of the galaxy cluster, ‘the researchers wrote in the newspaper.

The team initially selected 220 UCD candidates, and from this broad sample, they selected 44 with a higher probability that they would be true UCDs. Nearly all of the newly identified UCD candidates are located outside the core of the Fornax group (more than 1,170 light-years away from the center of the group).

According to the newspaper, it appears that nearly half of the newly discovered ultra-compact dwarf systems on the outskirts of the Fornax cluster are UCDs inside clusters, far beyond 650,000 light-years from any galaxy in this cluster brighter than -18 power. The astronomers noted that this group can form UCDs in low-density environments and represent the declining UCD populations in the group.

The study also identified two excessive densities of UCDs outside the core of the Fornax Cluster in the northern and western sides, which apparently overlap the improvement in the density of dwarf systems in this cluster. This finding suggests that the population of UCDs follows the dwarf systems in the Fornax group and can form, in low-density, preprocessed group environments, challenging our current models of UCD formation.

The authors of the article added that follow-up spectroscopy and radial velocity studies are needed to confirm the membership of the new UCD candidates. Such measurements will also shed more light on the origin of these UCDs.

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