Bibcode
Aparicio, Antonio; Marín-Franch, Antonio; Piotto, Giampaolo; Rosenberg, Alfred; Chaboyer, Brian; Sarajedini, Ata; Siegel, Michael; Anderson, Jay; Bedin, Luigi R.; Dotter, Aaron; Hempel, Maren; King, Ivan; Majewski, Steven; Milone, Antonino P.; Paust, Nathaniel; Reid, I. Neill
Referencia bibliográfica
PROBING STELLAR POPULATIONS OUT TO THE DISTANT UNIVERSE: CEFALU 2008, Proceedings of the International Conference. AIP Conference Proceedings, Volume 1111, pp. 222-229 (2009).
Fecha de publicación:
5
2009
Número de citas
1
Número de citas referidas
0
Descripción
The ACS Survey of Galactic Globular Clusters is a Hubble Space Telescope
(HST) Treasury program designed to provide a new large, deep and
homogeneous photometric database. Based on observations from this
program, we have measured precise relative ages for a sample of 64
Galactic globular clusters by comparing the relative position of the
clusters' main sequence turn offs, using main-sequence fitting to
cross-compare clusters within the sample. This method provides relative
ages to a formal precision of 2-7%. We demonstrate that the calculated
relative ages are independent of the choice of theoretical model. We
find that the Galactic globular cluster sample can be divided into two
groups-a population of old clusters with an intrinsic age dispersion of
~3% and no age-metallicity relation, and a group of younger clusters
with an age-metallicity relation similar to that of the globular
clusters associated with the Sagittarius dwarf galaxy. These results are
consistent with the Milky Way halo having formed in two phases. The
first phase would be compatible with a rapid (<0.8 Gyr) assembling
process of the halo, in which the clusters in the old group were formed.
The second phase lasted much longer in time and resulted in a group of
globular clusters with a clear age-metallicity relation. It is very
tempting to argue that the origin of this second group of clusters is
related to the accretion of Milky Way satellite galaxies, but the origin
of the age-metallicity relation remains unclear.