SED Fitting of the Globular Clusters in Abell 2744 at z=0.3

Abstract

We present a spectral energy distribution (SED) fitting analysis of globular cluster (GC) candidates in Abell 2744, a massive galaxy cluster at redshift z = 0.308 with a lookback time of 3.5 Gyr, using deep JWST/NIRCam photometry. By leveraging observations in eight broadband filters (F070W to F444W), we derive constraints on GC masses, ages, and metallicities of 69 GC candidates, refining previous studies focused on color-magnitude analysis. The inferred GC masses predominantly fall near 10^7 M_sun, consistent with the high-mass end of typical GCs seen in the Local Group and overlapping with UCDs (Ultra-Compact Dwarfs). Although the best-fit age estimates are unavoidably uncertain, we very tentatively identify two prominent concentrations: one at intermediate ages (4-6.5 Gyr) near [M/H]=-0.25; and a second at older ages 8 - 10 Gyr with both metal-poor ([M/H]=-0.66) and metal-rich ([M/H]=+0.15) components. As expected for broadband SED fitting, we find mass-age and age-metallicity degeneracies in our result. Monte Carlo error propagation and tests with different SSP model assumptions show that the population-level trends in age and metallicity are preserved, although individual age estimates must be interpreted with caution. The resulting mass-to-light ratios show wavelength dependence with a mild decline toward longer wavelengths and increase with age, while showing minimal sensitivity to metallicity. These results demonstrate the power and current limitations of multi-band JWST SED fitting that highlight the potential of future JWST data for detailed characterization of GCs at lookback times of several Gigayears.