Dwarf-to-dwarf mergers

When NGC4449’s smaller companion was first discovered as part of a search for nearby dwarf galaxies, the researchers involved speculated it might be a dwarf distorted during the merger of larger galaxies, or a dwarf about to be captured.  The new, thorough analyses by the two groups around Michael Rich and David Delgado-Martínez confirm that this is indeed a dwarf about to be gobbled up by the larger dwarf galaxy NGC 4449.

This is the first clear evidence for dwarf-dwarf-mergers. Previously, such mergers had already been under discussion as a mechanism for the formation of existing dwarf galaxies; however, it was also conceivable that such galaxies formed directly out of pristine gas.

The properties of NGC 4449 – elongated, with comparatively low surface brightness – also indicate what astronomers should be looking for to find further examples of dwarfs gobbling up dwarfs.

The fact that the dwarf pair is comparatively close to Earth, at a distance of about 12 million light-years, shows that such mergers are a necessary ingredient if we want to describe our cosmic neighbourhood, the “local universe”.


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