Pegasus V is an ultra-faint fossil dwarf galaxy that can offer clues to primordial galaxies

The ultra-faint dwarf galaxy Pegasus V
The ultra-faint dwarf galaxy Pegasus V

An article submitted for publication in the journal “Monthly Notices of the Royal Astronomical Society” reports the identification of an ultra-faint dwarf galaxy that was named Pegasus V near the Andromeda galaxy. A team of researchers conducted follow-up observations following the discovery made by an amateur astronomer and, using the GMOS instrument mounted on the Gemini North telescope in Hawaii, confirmed its existence. An interesting result of the observations is the very limited presence of elements heavier than hydrogen and helium, a discovery that led to the conclusion that it’s a kind of fossil of a primordial galaxy.

A dwarf galaxy of the ultra-faint type, which means that it has a very low brightness, may seem interesting only as an astronomical curiosity. However, certain characteristics may make it interesting for various cosmological studies. The very low brightness is due to a low amount of active stars, which are old and small, meaning no new stars are forming. This means that it’s a so-called fossil galaxy that is slowly dying. In the case of Pegasus V, it’s possible that nearby Andromeda had a negative influence on star formation but other results of its examination increase the interest in a dwarf galaxy discovered thanks to an amateur astronomer’s sharp sight.

The dwarf galaxy Pegasus V was just a speck in an archival image from the DESI Legacy Imaging Surveys, which were conducted for other types of astronomical research. The amateur astronomer Giuseppe Donatiello identified and reported it, allowing professional astronomers to investigate with follow-up observations. The picture (International Gemini Observatory/NOIRLab/NSF/AURA. Acknowledgment: Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab)) shows difficult it is to recognize the nature of Pegasus V. It took an examination of the stars within it to realize that it was a dwarf galaxy.

The GMOS (Gemini Multi-Object Spectrograph) instrument mounted on the Gemini North telescope made it possible to analyze the electromagnetic emissions from the dwarf galaxy Pegasus V mapping its composition. The result is the discovery of a very low percentage of elements heavier than hydrogen and helium. When several generations of stars follow each other, they produce more and more heavy elements. A very low amount means that the galaxy had just a few generations of stars. Pegasus V is close to Andromeda, so we see it as it was a few millions of years ago, which means that inside it, star formation must have been blocked billions of years ago. Basically, the conclusion is that Pegasus V is a fossil of the first galaxies in the universe.

The astronomers hope to find more clues to the early period of galaxy and star formation in the universe by continuing to study the dwarf galaxy Pegasus V. This also includes studying dark matter, as it will be possible to use it to test various models, including alternative ones that don’t predict its existence.

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