What Are Those Tiny Things? A First Study of Compact Star Clusters in the SMACS0723 Field with JWST
Abstract
We use the unprecedented resolution and depth of the JWST NIRCam Early Release Observations at 1–5 μm 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 mag fainter than the current depths of wide-field galaxy survey. The star clusters are unresolved in the NIRCam/F150W data suggesting sizes smaller than 50 pc. 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 0.2–0.3 Z_⊙ and ages of 1.5_(-0.5)^(+0.5) Gyr. We rule out metallicities <0.2 Z_⊙ and solar/supersolar at 4σ significance. Assuming mass-to-light ratios obtained from the best-fit SSP, we estimate stellar masses of 2.4_(-1.5)^(+3.0) x 10⁶ M_⊙. These are between average masses of local globular clusters and dwarf galaxies. Our analysis suggests middle-aged globular cluster with relatively recent formation times at z = 0.5–0.7, which could have been subsequently stripped away from their host galaxies due to interactions in the cluster environment or formed in cold flows onto the cluster core. However, we cannot rule out these objects being compact cores of stripped dwarf galaxies.
Additional Information
We thank Sergio Fajardo-Acosta, Alastair Edge, and Jessica Krick for fruitful discussions on the topic of stars and globular clusters. We also thank the anonymous referee for the helpful input, which significantly improved the quality of this manuscript. This research is partially funded by the Joint Survey Processing effort at IPAC/Caltech through NASA grant NNN12AA01C. This research made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant No. 140. This work has been based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with JWST programs 2736. The authors acknowledge the ERO teams led by Klaus M. Pontoppidan for developing their observing programs with a zero-exclusive-access period.Additional details
- Eprint ID
- 118616
- Resolver ID
- CaltechAUTHORS:20230103-817548100.8
- NNN12AA01C
- NASA/JPL/Caltech
- 140
- Danish National Research Foundation
- NAS 5-03127
- NASA
- Created
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2023-01-26Created from EPrint's datestamp field
- Updated
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2023-01-26Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)