Hidden in the Halo: New Diffuse Star Clusters in the M82 Starburst with JWST
Abstract
Diffuse star clusters (DSCs) occupy a poorly explored region of the size-luminosity plane between classical globular clusters (GCs) and dwarf galaxies. Here we report the discovery of four faint DSCs in the halo of the nearby starburst galaxy M82 using archival JWST/NIRCam imaging. We resolve individual stars in all four systems, whose color-magnitude diagrams are consistent with predominantly old (∼10 Gyr) stellar populations, based on comparison with isochrones. DSC 1 hosts a metal-poor population ([M/H]∼−2), while DSCs 2, 3 and 4 are better represented by [M/H]∼−0.8 isochrones. To establish their nature, we measure their sizes and integrated magnitudes using curve-of-growth and radial profile fits, which yield consistent results between these methods. The sizes of DSCs range from ∼ 5.4 to 10.5 pc, making them more extended than typical GCs (2-3 pc). Their luminosities span MV≃−4.1 to −6.4, reaching ∼ 1 mag fainter than the previously known M82 star cluster (SC) population. At these low luminosities, the systems occupy a sparsely sampled region of the size-luminosity plane where the distinction between SCs and dwarf galaxies becomes increasingly ambiguous. Most notably, DSC 3 is the faintest SC candidate identified in M82 to date and approaches the regime occupied by Milky Way ultra-faint compact satellites. These faint DSCs were identified through visual inspection alone, suggesting they are likely underrepresented in existing star cluster catalogs, and that a JWST-based archival search of nearby galaxies would be fruitful.
Related
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- SQuIGGL⃗E: Spatially resolved NIRSpec Paα reveals that the most CO-luminous, z∼0.7 post-starburst galaxies exhibit falling---but still active---star formation behind optically thick dust
- Statistical Modeling of Foreground Galactic Cirrus for Diffuse Halo Light Measurement
- The Deep Learning Halo Definer: A Multimodal Framework for Halo Mass and Gas Fraction Inference on Galaxy Groups and Clusters
BibTeX
@misc{prabhu2026hidden,
title = {{Hidden in the Halo: New Diffuse Star Clusters in the M82 Starburst with JWST}},
author = {Deepthi S. Prabhu and David J. Sand and Burcin Mutlu-Pakdil and Adam Smercina and Denija Crnojevic and Michael G. Jones and Paul Bennet and Amandine Doliva-Dolinsky and Kristine Spekkens and Debasish Hazarika and Laura Congreve Hunter and Jaclyn Jensen and Benjamin N. Velguth and Dennis Zaritsky and Sasha N. Campana},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30373},
eprint = {2609.30373},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30373},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Hidden in the Halo: New Diffuse Star Clusters in the M82 Starburst with JWST
AU - Deepthi S. Prabhu
AU - David J. Sand
AU - Burcin Mutlu-Pakdil
AU - Adam Smercina
AU - Denija Crnojevic
AU - Michael G. Jones
AU - Paul Bennet
AU - Amandine Doliva-Dolinsky
AU - Kristine Spekkens
AU - Debasish Hazarika
AU - Laura Congreve Hunter
AU - Jaclyn Jensen
AU - Benjamin N. Velguth
AU - Dennis Zaritsky
AU - Sasha N. Campana
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.30373
UR - https://arxiv.org/abs/2609.30373
AB - Diffuse star clusters (DSCs) occupy a poorly explored region of the size-luminosity plane between classical globular clusters (GCs) and dwarf galaxies. Here we report the discovery of four faint DSCs in the halo of the nearby starburst galaxy M82 using archival JWST/NIRCam imaging. We resolve individual stars in all four systems, whose color-magnitude diagrams are consistent with predominantly old (∼10 Gyr) stellar populations, based on comparison with isochrones. DSC 1 hosts a metal-poor population ([M/H]∼−2), while DSCs 2, 3 and 4 are better represented by [M/H]∼−0.8 isochrones. To establish their nature, we measure their sizes and integrated magnitudes using curve-of-growth and radial profile fits, which yield consistent results between these methods. The sizes of DSCs range from ∼ 5.4 to 10.5 pc, making them more extended than typical GCs (2-3 pc). Their luminosities span M_V≃−4.1 to −6.4, reaching ∼ 1 mag fainter than the previously known M82 star cluster (SC) population. At these low luminosities, the systems occupy a sparsely sampled region of the size-luminosity plane where the distinction between SCs and dwarf galaxies becomes increasingly ambiguous. Most notably, DSC 3 is the faintest SC candidate identified in M82 to date and approaches the regime occupied by Milky Way ultra-faint compact satellites. These faint DSCs were identified through visual inspection alone, suggesting they are likely underrepresented in existing star cluster catalogs, and that a JWST-based archival search of nearby galaxies would be fruitful.
ER -