(David Martínez-Delgado et al. / Monthly Notices of the Royal Astronomical Society, 2021)
An Italian amateur astronomer helped astronomers discover a dwarf satellite candidate for the large spiral galaxy M33.
If the discovery is further confirmed, it will help reduce the serious discrepancy between the observed and theoretical numbers of M33 satellites.
Spiral galaxy M33, located in the constellation of the Triangle, is the second largest spiral galaxy close to the Milky Way, making it visible to the naked eye in the night sky.
It is one of the brightest and most massive galaxies in the Local Group - its stellar mass is 3×109 solar masses, and the halo mass is estimated at 1011 solar masses.
The Lambda-CDM cosmological model predicts that at this mass, M33 should have from 9 to 25 satellite galaxies with stellar masses of more than 103 solar masses.
However, to date, only one potential satellite is known, the dwarf spheroidal galaxy Andromeda XXII, whose stellar mass is 2 × 104 solar masses.
In addition, astronomers note the lack of globular clusters found around M33 compared to other spiral galaxies.
This can be interpreted as features of the dynamic evolution of the galaxy.
Another interpretation is that our current understanding of the formation processes of low-mass galaxies is not entirely correct, and M33 in reality has a large number of satellites.
A group of astronomers led by David Martinez-Delgado of the Institute of Astrophysics of Andalusia announced the discovery of a candidate for a new satellite galaxy M33, designated Pisces VII (or Triangle III).
It is noteworthy that the original galaxy in the form of a dense region in the constellation Pisces was found by amateur astronomer Giuseppe Donatiello, who studied images of the vicinity of M33 from the DESI LIS surveys.
Subsequently, the discovery was confirmed by images from the SDSS DR9 catalog and observational data from the TNG telescope (Telescopio Nazionale Galileo).
An analysis of observational data for this faint, compact galaxy revealed that it is 72 kiloparsecs from M33 and one megaparsec from the Sun.
If it is a satellite galaxy M33, then its effective radius is 119 parsecs, if it is an isolated ultra-low galaxy, then its effective radius is 131 parsecs.
The final status of Pisces VII should be determined by new, more detailed observations using the Hubble Space Telescope and the Keck or Gemini ground observatories.
If this galaxy does turn out to be a satellite, then this will reduce the discrepancy between the observed and theoretical number of satellites of M33.
- Monthly Notices of the Royal Astronomical Society: https://academic.oup.com/mnras/article/509/1/16/6381713