Andromeda XXI

It is the fourth largest Local Group dwarf spheroidal galaxy.

This survey was conducted with the Megaprime/MegaCam wide-field camera mounted on the Canada-France-Hawaii Telescope.

This large satellite of the Andromeda Galaxy (M31) has a half-light radius of roughly 1 kpc.

It has red giant branches at the distance of M31/M33, and follows metal-poor, [Fe/H]=-1.8 when plotted in a color-magnitude diagram.

[3] Its central dark matter density is lower than expected from the ΛCDM model, but this could be explained if it lost most of its mass in a previous tidal stripping event or had experience tidal shocks from an eccentric orbit.