Gemini North telescope captures eroding remains of 100+ dwarf galaxies

Astronomers have captured the eroding remains of over 100 dwarf galaxies as they transition into ultra-compact dwarf galaxies (UCDs). UCDs - mystifying objects with masses much greater than star clusters yet much smaller than dwarf galaxies - are among the densest stellar groupings in the Universe.

The findings confirm that many UCDs are likely the fossil remnants of normal dwarf galaxies that have been stripped of their outer layers. Dwarf galaxies stripped of their stars prove to be the missing link in the formation of rare UCDs.

An international team of astronomers conducted a systematic search for these intermediate-stage objects around the Virgo Cluster, a group of thousands of galaxies in the direction of the constellation Virgo. Using the Gemini North telescope in Hawaiʻi, the team identified more than 100 of these missing-link galaxies that show every stage of the transformation process.

"Our results provide the most complete picture of the origin of this mysterious class of galaxy that was discovered nearly 25 years ago. Here we show that 106 small galaxies in the Virgo cluster have sizes between normal dwarf galaxies and UCDs, revealing a continuum that fills the ‘size gap’ between star clusters and galaxies," said NOIRLab astronomer Eric Peng, a co-author on the paper describing these results appearing in the journal Nature.

The team was able to identify hundreds of candidate UCD progenitors, but they were unable to confirm their true nature. UCDs surrounded by envelopes of stars are indistinguishable from normal galaxies that are located farther away beyond the Virgo Cluster.

With follow-up spectroscopic studies with Gemini North, the team was able to distinguish the candidate UCD progenitors from the background galaxies. This resulted in the elimination of all the background galaxies from their samples until only the UCDs within the Virgo Cluster remained.

The researchers also found many objects with very extended and diffuse stellar envelopes around them, indicating that they are currently in the throes of transitioning as their stars and dark matter is stripped away.