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Dozens of ultra-compact dwarf galaxies discovered

Dozens of ultra-compact dwarf galaxies discovered

UCD / GC 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 ultracompact dwarf galaxies (UCDs). The newly discovered sites most likely belong to the Fornax cluster. The discovery was announced in an article published March 31 on the arXiv prepress server.

UCDs are very compact galaxies with a high stellar population, containing about 100 million stars. They show masses, colors, and metals between those of globular clusters and early dwarf galaxies. These ultra-compact star systems could provide important information about the formation and evolution of galaxies in the universe.

Located about 65 million light-years from Earth, the Fornax cluster is the second richest cluster of nearby galaxies. Due to its relatively close proximity, it is a valuable source of information about galactic clusters in general. Previous observations of the Fornax Cluster have found a total of 61 UCD members.

Now a group of astronomers led by Teymoor Saifollahi of the University of Groningen, the Netherlands, is announcing the discovery of dozens of new potential UCDs that could be linked to the Fornax cluster. Analyzing data from the Fornax Deep Survey (FDS), Vista Hemisphere Survey (VHS) and archives from the Visible and Infrared Survey (VISTA) astronomy telescope, they identified 44 UCD candidates on the outskirts of this cluster.

“With the deep optical images of the Fornax Deep Survey combined with public near-infrared data, we are reviewing the UNA population of the Fornax cluster and, for the first time, systematically looking for UCD candidates up to the viral radius of the galaxy cluster,” the researchers wrote.

Initially, the team selected 220 UCD candidates and selected 44 from this large sample who are more likely to be true UCDs. Almost all newly discovered UCD candidates are located outside the core of the Fornax cluster (more than 1170 light-years from the center of the cluster).

According to the article, nearly half of the newly discovered ultracompact dwarf galaxies on the fringes of the Fornax cluster appear to be intraclustered UCDs more than 650,000 light-years away from each galaxy in that cluster, brighter than -18 mag. Astronomers have noted that this group of UCDs can form in a low-density environment and represent falling populations of UCDs in the cluster.

The study also identified two UCD superdensees outside the core of the Fornax cluster on the north and west sides that appear to overlap with improvements in the density of dwarf galaxies in that cluster. This finding suggests that the UCD population follows the dwarf galaxies in the Fornax cluster and can form in a pre-treated low-density group environment, which challenges our current UCD formation patterns.

The authors of the article add that subsequent spectroscopy and radial velocity studies are needed to confirm the membership of new UCD candidates. Such measurements would also shed more light on the origin of these UCDs.

The galactic census reveals the origins of most “extreme” galaxies

More information:
Ultra-compact dwarfs beyond the center of the Fornax galaxy cluster: Tips for forming UCDs in low-density environments, arXiv: 2104.00004 [astro-ph.GA] arxiv.org/abs/2104.00004

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Quote: Dozens of discovered ultra-compact dwarf galaxies (2021, April 8) extracted on April 9, 2021 from https://phys.org/news/2021-04-dozens-ultra-compact-dwarf-galaxies.html

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