The estimated distance of Aquarius 2 from the Milky Way is ~360,000 light years and its estimated half-light radius is ~500 light years. The half-light radius of a galaxy is the size of the volume around the center of the galaxy which accounts for half the galaxy's brightness. The half-light radius of Aquarius 2 is estimated to enclose ~3 million times the Sun's mass.
Aquarius 2 has a low surface brightness of only 30.4 mag/arcsec², and the total luminosity of this dwarf galaxy is only ~4000 times the Sun's luminosity. Aquarius 2 has a large mass-to-light ratio of ~1300, indicating it is a dark matter dominated galaxy. The low surface brightness and low overall luminosity of Aquarius 2 makes it a particularly difficult galaxy to detect. The detection of Aquarius 2 suggests the presence of more dwarf galaxies lurking out there.
The red solid line denotes the elliptical half-light contour of the best fit model for Aquarius 2. The orange, red and blue circles/squares mark the locations of stars confirmed as foreground, RGB and BHB stars, respectively. Torrealba et al. (2016)
Absolute magnitude versus half-light radius for Milky Way satellite galaxies (red open circles), M31 satellite galaxies (black unfilled triangles), globular clusters (black dots), extended objects larger than ~300 light years in size (grey dots) and Local Group/nearby galaxies (grey crosses). Torrealba et al. (2016)
Torrealba et al. (2016), "At the survey limits: discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data", arXiv:1605.05338 [astro-ph.GA]