Four and one more: The formation history and total mass of globular clusters in the Fornax dSph

Abstract

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 were constructed in the F555W and F814W bands and corrected for the effect of Fornax field star contamination, after which we used 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. Clusters Fornax 1, 2, and 3 display metallicities as low as [Fe/H] = −2.5, while Fornax 5 is slightly more metal-rich at [Fe/H] = −1.8, consistent with resolved and unresolved metallicity tracers. Conversely, Fornax 4 is dominated by a more metal-rich ([Fe/H] = −1.2) and younger population at 10 Gyr, inconsistent with the other clusters. A lack of stellar populations overlapping with the main body of Fornax argues against the nucleus cluster scenario for Fornax 4. The combined stellar mass in globular clusters as derived from the SFH is (9.57 ± 0.93) × 10 5 M , which corresponds to 2.5 ± 0.2 percent of the total stellar mass in Fornax. The mass of the four most metal-poor clusters can also be compared to the metal-poor Fornax field to yield a mass fraction of 19.6 ± 3.1 percent. Therefore, the SFH results provide separate supporting evidence for the unusually high mass fraction of the globular clusters compared to the Fornax field population.

Little Blue Dots in the Hubble Space Telescope Frontier Fields: Precursors to Globular Clusters?

“…A further comparison is with the early SFRs for the globular clusters in the Fornax dSph galaxy, as determined by de Boer & Fraser (2016). From their figure 8, the peak rates for Fornax globular clusters 1-5 are, in units of 10 −5 M ⊙ yr −1 , approximately: 2, 6, 16, 2, and 4.5, with an rms of about 1 to 2 in these units.…”

Embedding globular clusters in dark matter minihaloes solves the cusp–core and timing problems in the Fornax dwarf galaxy

“…where r s and M 0 = 3.82 × 10 7 M are the scale parameter and the mass, respectively (de Boer & Fraser 2016). For the DM halo of Fornax, we assume a NFW form (Navarro et al 1996): , determined by using Illustris TNG-100 data.…”

Fornax globular cluster distributions: implications for the cusp-core problem

“…The dSph galaxy Fornax is one of the most dark matter-rich satellites of the Milky Way with a mass of about 10 8 M at a distance of around 147 kpc (de Boer & Fraser 2016). Fornax contains five globular clusters with masses of about 10 5 M and the average projected distance of these clusters is about 1 kpc.…”

“…We performed our simulations with the N-body code of -2 (Springel (2005)). We create, for each Fornax mass model, initial conditions for the Fornax-globular clusters system and evolve them for 12 Gyr because the Fornax globular clusters are all dominated by ancient (>10 Gyr) populations of stars (de Boer & Fraser 2016).…”