http://arxiv.org/abs/2208.05502
We use the unprecedented resolution and depth of the JWST NIRCam Early Release Observations (ERO) at 1-5$\mu m$ to study the stellar mass, age, and metallicity of compact star clusters in the neighborhood of the host galaxies in the SMACS J0723.3-7327 galaxy cluster field at z = 0.39. The measured colors of these star clusters show a similar distribution as quiescent galaxies at the same redshift, but are >3 magnitudes fainter than the current depths of wide-field galaxy survey. The star clusters are unresolved in the NIRCam/F150W data suggesting sizes smaller than 50pc. This is significantly smaller than star forming clumps or dwarf galaxies in local galaxies. From fitting their photometry with simple stellar population (SSP) models, we find stellar metallicities consistent with 0.2-0.3Z${\odot}$ and ages of $5.0^{+0.5}{-1.1}$ Gyrs. We rule out ages of <3 Gyrs at a 2$\sigma$ confidence, and metallicities <0.2 Z${\odot}$ and solar/super-solar at 4$\sigma$ significance. Assuming the mass-to-light ratio (1.22 M${\odot}$/L${\odot}$) obtained from the best-fit SSP, we estimate stellar masses of $4.1^{+3.5}{-1.8}\times10^6\,{\rm M_{\odot}}$. These are between average masses of local globular clusters and dwarf galaxies. Our analysis suggests middle-aged globulars with relatively recent formation times at z=1-2, which could be subsequently stripped away from their host galaxies due to interactions in the cluster environment. However, we cannot rule out these objects being compact cores of stripped dwarf galaxies.
A. Faisst, R. Chary, G. Brammer, et. al.
Fri, 12 Aug 22
6/48
Comments: 16 pages, 7 figures, 2 tables. Submitted to ApJ
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