Segue 3 : the youngest globular cluster in the outer halo

Abstract

Deep Galileo (Telescopio Nazionale Galileo) B, V and I images of Segue 3, reaching V ∼ 25, reveal that it is the youngest globular cluster known so far in the Galaxy.Ayoung age of 3.2 Gyr is found, differently from a previous estimate of 12Gyr. It also appears to be moderately metal rich with [Fe/H]∼−0.8, rather than [Fe/H]∼−1.7, as previously suggested by Fadely et al. A main difference in the age derivation relative to Fadely et al. comes from the consideration of subgiant branch stars in the isochrone fitting. A deduced distance of d = 29.1 kpc is compatible with the outer halo location of other low luminosity globular clusters.