An article being published in “The Astrophysical Journal” reports the results of the study of two galaxy mergers between dwarf galaxies with active galactic nuclei. A team of researchers used data collected by NASA’s Chandra X-ray Observatory to discover candidates and then compared them with infrared observations conducted with NASA’s WISE Space Telescope and optical frequency observations conducted with the Canada-France-Hawaii Telescope (CFHT).
Astronomers think that massive galaxies formed through mergers, and supermassive black holes could play an important role in these processes. However, the light from primordial dwarf galaxies is so dim that it’s nearly impossible to detect even for the most advanced instruments. Consequently, studying mergers between relatively close dwarf galaxies is important for reconstructing events that occurred when the universe was young. So far, the search for these mergers was unsuccessful too, so a group of researchers planned a systematic search to locate them.
Even dwarf galaxies appear to have supermassive black holes at their centers. If they are surrounded by large amounts of gas and dust that are heated considerably, they have an active galactic nucleus that can be very bright and make even a dwarf galaxy clearly visible. Finding pairs of active galactic nuclei in merging dwarf galaxies is difficult but the authors of this research found two pairs by combining observations at X-rays from the Chandra X-ray Observatory, at infrareds conducted with the WISE Space Telescope, and at optical frequencies conducted with the CFHT.
The image (X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA) shows the merging dwarf galaxy pairs object of this study in a combination of X-ray and optical frequency observations.
About 760 million light-years from Earth, in the Abell 133 galaxy cluster, the researchers found a pair of dwarf galaxies in an advanced stage of the merger. Tidal effects caused by gravitational interactions between the original dwarf galaxies generated a long tail. The new galaxy, still forming, was dubbed Mirabilis after the marvelous spatuletail (Loddigesia mirabilis), a critically endangered species of hummingbird known for its long tail.
About 3.2 billion light-years from Earth, in the Abell 1758S galaxy cluster, the researchers found a pair of dwarf galaxies in a merging stage in which they can still be distinguished. The researchers nicknamed the two dwarf galaxies Elstir (at bottom of the image) and Vinteuil after two characters from Marcel Proust’s novel “In Search of Lost Time”. A bridge of stars and gas already formed between the two dwarf galaxies but it will still take a long time to see significant deformations in their shapes.
Studying the processes at work in mergers between dwarf galaxies will provide further insight into the formation of massive galaxies. Observations of the very distant universe, which means the primordial universe, suggest that massive galaxies began forming very early. That’s difficult to explain with current models, so it’s important to collect information on galaxy mergers, including the ones closest to us.