Considering the ever increasing number of studies on UDGs, there are still controversial results on their formation and dark matter (DM) content. In particular, it is not clear whether UDGs are a separate class of objects, different from all the other known Hubble types, or if they are simply dwarf galaxies with a very low fraction of baryonic versus DM content, which might be due to a different evolutionary path. As consequence, the formation mechanism for UDGs is still a matter of debate.
Studying UDGs’ structure and formation can provide important constraints on the consolidated ideas of galaxy formation and the relation between DM and ordinary matter. In fact, except for tidal dwarfs (e.g. Lelli et al. 2015), the formation of a galaxy relies on the existence of a gravitationally dominant DM halo (White & Rees 1978). The discovery of some UDGs with no-DM (van Dokkum et al. 2016, 2019b; Danieli et al. 2019) has a strong impact on the general framework of galaxy formation, in order to account for such large, baryon dominated and relative massive stellar systems.
To date, the main limitation in this research area is the small number of detected UDGs compared to the other galaxy types, due to the low surface brightness of these systems. This further limits also the spectroscopic follow-ups which allow to study their kinematics and stellar population.
With the UltraVEGAS project, started in 2020, we can overcome the above limits by exploiting the homogeneous VEGAS data set in the LSB regime. The new catalogue of UDGs provided by UltraVEGAS will double the number of studied UDGs and will have a legacy value for future follow-up imaging and spectroscopic observations.
