Вадим Дудченко
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Named Pisces VII/Triangulum (Tri) III, the newly-discovered galaxy is an ultra-faint dwarf satellite candidate of the Triangulum galaxy (also known as Messier 33 or M33).

This image shows Pisces VI/Tri III, a dwarf galaxy located 3.2 million light-years away in the constellation of Pisces. Image credit: DESI Legacy Imaging Surveys.

Pisces VII/ Tri III was discovered in the Pisces constellation by the amateur astronomer Giuseppe Donatiello using the public imaging data from the DESI Legacy Imaging Surveys.

The discovery was subsequently confirmed by a visual inspection of the SDSS DR9 images and follow-up observations using the Italian Telescopio Nazionale Galileo.

Pisces VII/ Tri III lies at a projected distance of 72,000 parsecs (234,833 light-years) from the Triangulum galaxy.

It could either be an isolated ultra-faint or the second known satellite of the Triangulum galaxy.

“Theoretical knowledge about galaxy formation means we’d expect to see many more little galaxies orbiting the Triangulum galaxy,” said Emily Charles, a Ph.D. student in the Physics Department at the University of Surrey.

“However, so far it only has one known satellite.”

“If this newly identified galaxy does belong to the Triangulum galaxy, it might imply that there are many more that haven’t been uncovered yet as they are too faint to show up in previous surveys of the system.”

“The Triangulum galaxy currently challenges astrophysicists’ assumptions, but this new finding starts reassuring us that our theories are correct.”

In order to confirm whether Pisces VII/ Tri III is isolated or a satellite of the Triangulum galaxy, the astronomers need to accurately measure the distance to the galaxy and see how it is moving compared to the larger companion.

Both require further imaging using other telescopes.

“Deep imaging from Hubble would allow us to reach fainter stars which act as more robust distance estimators, as they have a standard brightness,” said Noushin Karim, a Ph.D. student in the Physics Department at the University of Surrey.

“To confirm the new galaxy’s movement, we need imaging from an 8-m or 10-m telescope, like Keck or Gemini.”

The team’s paper appears in the Monthly Notices of the Royal Astronomical Society.


David Martínez-Delgado et al. 2022. Pisces VII: discovery of a possible satellite of Messier 33 in the DESI legacy imaging surveys. MNRAS 509 (1): 16-24; doi: 10.1093/mnras/stab2797


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