Astronomers discover Andromeda XXXVI, an ultra-faint dwarf satellite galaxy
By analyzing the data from the Pan-Andromeda Archaeological Survey (PandAS), European astronomers have discovered a new satellite of the Andromeda galaxy. The newfound object, which received the designation Andromeda XXXVI, appears to be an ultra-faint dwarf galaxy. The finding is reported in a paper published March 30 on the arXiv preprint server .
Small and faint satellites of the Milky Way’s neighbor
The so-called ultra-faint dwarf galaxies (UFDs) are the least luminous, most dark matter-dominated, and least chemically evolved galaxies known. Therefore, they are perceived by astronomers as the best candidate fossils from the universe at its early stages.
Now, a team of astronomers, led by Joanna D. Sakowska of the Institute of Astrophysics of Andalusia in Spain, reports the finding of a new UFD. Andromeda XXXVI was first spotted and classified as a candidate UFD by amateur astronomer Giuseppe Donatiello during a systematic, visual inspection search of public images from the full PAndAS footprint. Sakowska and her colleagues recently performed follow-up deep imaging of Andromeda XXXVI with the Roque de los Muchachos Observatory, which confirmed the UFD nature of this galaxy.
The astronomers identified Andromeda XXXVI as a compact object near the Andromeda galaxy, also known as Messier 31 (M31). They managed to resolve enough stars of this UFD to construct its color-magnitude diagram (CMD) and to characterize its structural and luminosity properties.
The properties of Andromeda XXXVI
According to the study, Andromeda XXXVI is located some 2.53 million light years away from Earth and about 388,000 light years away from the Andromeda galaxy. Given that Andromeda has a viral radius of about 850,000 light years, these distance estimates indicate that the newfound UFD is most likely its satellite.
The observations found that Andromeda XXXVI has a visual magnitude of -6.0, a half-light radius of 208 light years, and an ellipticity of approximately 0.015, which makes it one of the faintest, and potentially the second-most compact UFD satellite of the Andromeda galaxy. The metallicity of the UFD was measured to be at a level of -2.5, and its age was estimated to be 12.5 billion years.
Many UFDs still undetected
It is estimated that Andromeda hosts nearly 100 dwarf satellites and only about half of them are currently known. Therefore, the astronomers noted that the discovery of Andromeda XXXVI could be a major step toward disclosing the full population of very faint satellites of this galaxy. Moreover, their study underscores the importance of visual inspection when it comes to detection of UFDs around Andromeda.
“The discovery of Andromeda XXXVI highlights that visual inspection remains very complementary to automatic and machine learning approaches, using resolved and/or semi-resolved data. Both methods in combination thus remain crucial towards constructing a complete picture of Andromeda,” the researchers concluded.
Source: phys.org
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Astronomers discover Andromeda XXXVI, an ultra-faint dwarf satellite galaxy