THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. VII. RELATIVE AGES

By A. Marín-Franch, A. Aparicio, G. Piotto, A. Rosenberg, B. Chaboyer, A. Sarajedini, M. Siegel, Jay Anderson, L. Bedin, Aaron Dotter and 6 more. 2008

364 citations recorded by the source corpus.

The ACS Survey of Galactic globular clusters is a Hubble Space Telescope 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 (MS) turnoffs, using MS 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 age dispersion of ∼5% 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 or processes. The first one would be compatible with a rapid (<0.8 Gyr) assembling process of the halo, in which the clusters in the old group were formed. Also these clusters could have been formed before re-ionization in dwarf galaxies that would later merge to build the Milky Way halo as predicted by ΛCDM cosmology. However, the galactocentric metallicity gradient shown by these clusters seems difficult to reconcile with the latter. As for the younger clusters, it is very tempting to argue that their origin is related to their formation within Milky Way satellite galaxies that were later accreted, but the origin of the age–metallicity relation remains unclear.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9520fc3c8c91fae7b60824fecea20a86da8edc1b

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In Astronomy and Astrophysics

1. Jay Anderson
2. G. Piotto
3. R. Gratton
4. E. Carretta
5. A. Bragaglia
6. A. Milone
7. L. Bedin
8. F. D’Antona

In Instrumentation

1. Jay Anderson
2. E. Carretta
3. R. Gratton
4. A. Bragaglia
5. F. D’Antona
6. G. Piotto
7. A. Renzini
8. L. Bedin

Citations in the corpus

• THE CHEMICAL EVOLUTION OF THE DRACO DWARF SPHEROIDAL GALAXY (2009, background): “Many of the most distant Galactic GCs, which tend to show somewhat younger ages than the inner halo GCs (see, e.g. Marin-Franch et al 2009), are now believed to have been accreted by the Milky Way.”
• Accreted versus in situ Milky Way globular clusters (2010, methodology): “1 = Marin-Franch et al. (2009); 2 = de Angeli et al. (2005); 3 = Salaris & Weiss (1998); 4 = Carraro et al. (2007); 5 = Carraro (2009); 6 = Bellazzini et al. (2002); 7 = Carraro & Bensby (2009); 8 = Lee (1997); 9 = Frinchaboy et al. (2008).”
• ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, methodology): “The Age-Metallicity Relation and Horizontal Branch Morphology of Sgr Globular Clusters In Figure 12 (left panel), we plot the ages and metallicities (drawn from tabulations by Marin-Franch et al. 2009, and Forbes & Bridges 2010) of our eleven high/moderate/low confidence Sgr globular clusters.”
• Properties of stellar generations in globular clusters and relations with global parameters (2010, methodology): “In addition, we considered the relative age parameter, mostly re-determined from Marin-Franch et al. (2009) and De Angeli et al. (2005) as described in the Appendix.”
• THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. I. OVERVIEW OF THE PROJECT AND DETECTION OF MULTIPLE STELLAR POPULATIONS (2014, methodology): “Relative ages of 64 globular clusters were measured in the ACS Treasury Program of Galactic Globular Clusters (Marin-Franch et al. 2009).”
• Stellar population models at high spectral resolution (2011, methodology): “This may highlight that the SED-fitderived metallicities mostly reflect [Fe/H] rather than the total metallicity [Z/H] that both Marin-Franch et al. (2009) and the TMJ models aim to trace.”