Terzan 5, a fossil relic of the Galactic Bulge

Terzan 5 is a globular cluster-like system located at just 2.1 [Kpc] away from the Galactic center (l=3.84°, b=1.69°) that has been commonly cataloged as a Globular Cluster (GC) since its discovery. The high extintion (E(B-V)=2.38) and the strong differential reddening (ΔE(B-V)≈0.7mag) that characterize the area, in addition to the contamination from field stars, limited a deep photometric study of the stellar system. Recently (Ferraro et al. 2009), it has been discovered that this system is even more complex than previously thought, having two Horizontal Branches (HBs) separated by ~0.3 [mag] in the Ks band. This offset is explicable considering the presence of two population with a difference in metallicity and age of 0.5 [dex] and ~7 [Gyr], respectevely. Later studies (Origlia et al. 2011; Ferraro et al. 2016) confirmed the presence of two population, classifying Terzan 5 as a candidate for the building blocks of the Galaxy. Hence, it is so important to find the properties of this system in a precise way to elucidate the formation and the evolution history in the earliest time of the Milky Way. Recently we obtain new data in J and Ks bands with the near-infrared adaptive-optics camera GeMS/GSAOI of the inner part of this stellar system. In this work we will present the last results of the photometric analysis