http://arxiv.org/abs/1510.05642
We have determined the detailed star formation history and total mass of the globular clusters in the Fornax dwarf spheroidal using archival HST WFPC2 data. Colour magnitude diagrams are constructed in the F555W and F814W bands and corrected for the effect of Fornax field star contamination, after which we use the routine Talos to derive the quantitative star formation history as a function of age and metallicity. The star formation history of the Fornax globular clusters shows that Fornax 1, 2, 3 and 5 are all dominated by ancient~(>10 Gyr) populations. Cluster Fornax 1 and 3 display metallicities as low as [Fe/H]=-2.5 while Fornax 2 and 5 are slightly more metal-rich at [Fe/H]=-2.0, consistent with resolved and unresolved metallicity tracers. Conversely, Fornax 4 displays a more extended star formation history dominated by metal-rich~([Fe/H]=-1.4 dex) stars, with an age of ~10 Gyr, inconsistent with the other clusters. Its central location and complex population mix favours the proposed model that it might be the nucleus of the Fornax dwarf spheroidal. The combined stellar mass in globular clusters as derived from the SFH is (9.73$\pm$0.79)$\times$10$^{5}$ M$_{\odot}$ which corresponds to 2.5$\pm$0.2 percent of the total stellar mass in Fornax. This mass can be further subdivided into metal-poor stars to yield a mass fraction of 9.4$\pm$1.3 percent of the metal-poor Fornax field, or 19.1$\pm$2.8 percent when considering just the full mass of the four most metal-poor clusters. Therefore, the SFH results provide separate supporting evidence for the unusually high mass fraction of the GCs compared to the Fornax field population.
T. Boer and M. Fraser
Wed, 21 Oct 15
58/66
Comments: 9 pages, 8 figures. Submitted to A&A. comments welcome
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