Astronomers have discovered a tiny dwarf satellite galaxy in Andromeda (19459000).
The smallest, dimmest and tiniest galaxies have been identified as ultra-faint galaxies. They are vulnerable because of their low gravitational force to the cosmic processes which shape galaxy evolution. These include powerful stellar wind or early reionization.
These galaxies have been classified as “reionization-fossils,” meaning that their majority of stars were formed prior to reionization, and they’ve remained largely static ever since. These oldest fossils provide information about galaxy formation before the reionization.
The dark-matter-dominated system that is most prevalent in the universe are ultra-dwarf galaxies.
The number and distribution of these galaxies in space can provide astronomers with important information about the dark matter “subhaloes”, which surround large galaxies.
In the past, a lot of knowledge on ultra-faint galaxies was based upon those in our Milky Way. This is because it’s the only galaxy that we can rely upon, which may lead us to have a very narrow perspective. The study of ultra faint dwarf galaxies within other galaxies allows us to gain an understanding of galaxy development and dark matter.
NASA releases the biggest image ever of the Andromeda Galaxy
Andromeda XXXVI was discovered as part of Pan-Andromeda Archaeological Survey. Its existence has been confirmed by deep imaging using OSIRIS+ @ GTC.
Andromeda is an important player in the universe, with its own dark matter halo, which may conceal substructures.
It is therefore an excellent “laboratory” to study and discover ultra-faint galaxies. The Andromeda galaxy contains more than 40 dwarf satellite galaxies. About 16 are classified as Ultra-Faint Dwarfs.
The search for dwarf galaxies has been enhanced by wide-field surveys like SDSS, PanSTARRS and DESI & UNIONS. The data collected allows for astronomers discover faint galaxies either by analyzing stacked images in detail or clustering red giant branch star, which is confirmed through deeper observations.
Giuseppe Donatiello, an amateur astronomer, discovered Andromeda XXXVI by analyzing public images taken from the Pan-Andromeda Archaeological Survey.
The object is located 119 km from Andromeda and well outside the virial radius (260-260/2) of the galaxy.
Milky Way and Andromeda may never collide
Andromeda is truly in orbit with And XXXVI because of its orbital closeness. This will help astronomers gain more knowledge about the halo that surrounds our spiral galaxy neighbor and also provide insight on how galaxies form and the structure of Dark Matter.
Astronomers estimate And XXXVI to have an absolute magnitude -6.0 +/- 0.2 at a distance 776 kpc. This corresponds to a brightness 21.500x that of the Sun. It is a compact galaxy with a half light radius of 64pc and a low degree of ellipticity.
XXXVI will likely be classified as a ultra-dwarf satellite (UFD), compared to analog systems of the Milky Way or M31. This dwarf galaxy is one of the most faint and compact galaxies found so far in M31.
Notes by the Author The discovery of And XXXVI contributes to M31’s very low-luminosity satellite luminosity, indicating the existence of a larger population of extremely faint satellites.
To better determine its location within the halo of M31, deeper space-based observations and/or spectroscopic measurements are required. Combined with a detailed history of star formation, these data could help determine if its metal-poor, old stellar population is indicative of early quenching. Similar to trends observed in Milky Way Satellites. And XXXVI may be considered a reionization “fossil”.
The most detailed radio image yet of the Andromeda Galaxy
To fully characterize Andromeda (Andromeda XXXVI), astronomers will require follow-up data on stellar motion (kinematics). Finding brighter stars at the end of the TRGB would be helpful in confirming its faint intrinsic luminosity, but also in refining its distance.
It would be possible to determine when And XXXVI stopped forming stars if it is indeed old and deficient in metals. This could then be determined by mapping the star formation history of And XXXVI.
This would be a fascinating question if it qualifies as a fossil of reionization.
This discovery highlights the importance visual inspections in astronomy. Visual inspection of data that is semi-resolved remains important, even though machine learning and automated search can be valuable. These methodologies give a more complete picture of Andromeda’s dimmest partners and the mechanisms which shaped the formation of galaxies in the early Universe.
Journal Reference
- Joanna D. Sakowska, David Martinez-Delgado, Michelle L. M. Collins et al.
Andromeda XXXVI : Discovery of a new, ultra-faint galaxy toward M31. ArXiv (206). DOI: 10.48550/arxiv.2603.28492
