Relative ages of Galactic globular clusters. Clues to the Milky Way formation time scales

Dr. Antonio Marín-Franch

Abstract

Based on observations with the Advanced Camera for Surveys (ACS), I will present accurate relative ages for a sample of 64 Galactic globular clusters. This Hubble Space Telescope (HST) Treasury program has been designed to provide a new large, deep and homogeneous photometric database. Relative ages have been obtained using a main sequence fitting procedure between clusters in the sample. Relative ages are determined with an accuracy from 2% to 7%. It has been proved that derived ages are independent of the assumed theoretical models. The existence of two well defined Galactic globular cluster groups is found. A group of old globular clusters with an age dispersion of 6% and showing no age-metallicity relation, and, on the other hand, a younger group showing a clear age-metallicity relation similar to that found in the globular clusters associated to the Sagittarius dwarf galaxy. Roughly 1/3 of the clusters belong to the younger group. Considering these new results, it is very tempting to suggest a Milky Way's halo formation scenario in which two differentiated phases took place. A very fast collapse, where the old and coeval globular clusters where formed, followed by accretions of Milky Way's satellite galaxies.

About the talk

Relative ages of Galactic globular clusters. Clues to the Milky Way formation time scales
Dr. Antonio Marín-Franch
Instituto de Astrofísica de Canarias, Spain
Monday October 27, 2008 - 0:00  (Aula)
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