The ages and metallicities of the globular clusters in the Sparkler

Abstract

ABSTRACT JWST observations of the strongly lensed galaxy the Sparkler have revealed a population of gravitationally bound globular cluster (GC) candidates. Different analyses have resulted in broadly similar ages but significantly different metallicities, questioning the assembly history that has led to the formation of such a population. In this letter, we reanalyse the two sets of photometry available in the literature with the code mcmame especially tailored to fit physical properties of GCs. We find the ages and metallicities from both data sets are consistent within 1σ uncertainties. A significant group of GCs is consistent with being old and metal poor ([Fe/H] ∼ −1.7). For this group, the ages do not converge, hence, we conclude that they are definitively older than 1 Gyr and can be as old as the age of the Universe. The remaining GCs have younger ages and a metallicity spread. The ages and metallicities distribution of GCs in the Sparkler are consistent with those observed in Local Group’s galaxies at similar lookback times. Comparing with predictions from E-MOSAICS simulations we confirm that the Sparkler GC population traces the self-enrichment history of a galaxy which might become a few times 109 M⊙ massive system at redshift z = 0.