title: The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge.
abstract: Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short timescale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (omega Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age. Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron contents and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.
authors: Department of Astronomy, University of Bologna, Via Ranzani, 1, 40127 Bologna, Italy. francesco.ferraro3@unibo.it
authors: F R
authors: FR
authors: Ferraro
authors: E
authors: E
authors: Dalessandro
authors: A
authors: A
authors: Mucciarelli
authors: G
authors: G
authors: Beccari
authors: R M
authors: RM
authors: Rich
authors: L
authors: L
authors: Origlia
authors: B
authors: B
authors: Lanzoni
authors: R T
authors: RT
authors: Rood
authors: E
authors: E
authors: Valenti
authors: M
authors: M
authors: Bellazzini
authors: S M
authors: SM
authors: Ransom
authors: G
authors: G
authors: Cocozza