Faint stellar systems in the outer halo of the Milky Way
Filippo Contenta
University of Surrey

In a luminosity vs half-light radius diagram, globular clusters and dwarf galaxies are separated in radius at high luminosities (Mv we performed a survey of direct N-body simulations, in a Milky Way-like potential, of clusters that dissolve between 8 and 12 Gyr. In these last 4 Gyr, considering all observable stars, we found that the size of the cluster changes, due to the orbital motion and the surface density background (SDB).
The tidal modulation, caused by the orbital motion, allows the cluster to look bigger at apocentre than pericentre. Besides, simulating the SDB of a Milky Way-like galaxy, we found that the size of the same cluster is smaller with a Koposov1-like SDB than with a Willman1-like SDB.
It is therefore possible that some of the objects, that were classified as ultra-faint galaxies, because of their large sizes, are, in fact, nearly dissolved star cluster in apocentre with a low SDB.
Remarkable fluctuations has been seen in the evolution of the velocity dispersion due to a not stable size of the cluster. Moreover, we will have an analytic prediction on how many nearly dissolved star clusters we should expect in the halo of Milky Way.
In conclusion, we believe that this study could shed more light on the nature of extended objects in the outer Milky Way halo.