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arXiv · 2610.02606

Star Cluster Populations in 38 Spiral Galaxies: Evidence for Near-Universal Mass and Age Distributions from PHANGS

Rupali Chandar·Matthew R. Floyd·David A. Thilker·Kiana Henny·Bradley C. Whitmore·Janice C. Lee·Sinan Deger·Daniel A. Dale·Kirsten L. Larson·Mederic Bouquien·Oleg Gredin·Daniel Maschmann·Adam K. Leroy·Erk Rosolowsky·Leonardo Ubeda·Ashley T. Barnes·Eva Schinnerer·Eric Emsellem·Angus Mok·Kathryn Grasha·Francesca Pinna·Aida Wofford·Ralf S. Klessen·Simon Glover·Sumit K. Sarbadhicary·Ivan Gerasimov
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Abstract

We present the largest study to date of star cluster mass and age distributions in nearby galaxies. The analysis is based on a uniformly selected catalog of over 15,000 (36,000) human (machine) classified compact clusters across 38 spiral galaxies in the PHANGS-HST survey, with improved photometric SED age dating that mitigates key degeneracies with reddening and metallicity. The galaxies span a factor of ~100 in star formation rate (SFR) and in their surface density of star formation and molecular gas (Sigma_SFR, Sigma_H2), and cover a broad range of morphologies. We find that cluster mass functions are well described by a power law, dN/dM ~ M^beta, with beta=-1.9 +/- 0.2, and that this shape is remarkably similar across all galaxies in our sample and eight composite groups of galaxies with similar SFRs, with no significant dependence on SFR, Sigma_SFR}, or Sigma_H2. Cluster age distributions decline steeply and can be described by dN/dt ~ t^gamma with gamma=-0.83 +/- 0.24, again with little dependence on host-galaxy properties or cluster mass. The independence of the mass and age distributions implies a separable joint distribution, g(M,t) ~ M^beta t^gamma, and suggests that cluster populations in spiral disks are dominated by strong, mass-independent dissolution over their first ~Gyr. These results establish a benchmark for interpreting cluster demographics across diverse galactic environments and provide context for studies of young cluster populations at high redshift.

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Rupali Chandar, Matthew R. Floyd, David A. Thilker, Kiana Henny, Bradley C. Whitmore, Janice C. Lee, Sinan Deger, Daniel A. Dale, Kirsten L. Larson, Mederic Bouquien, Oleg Gredin, Daniel Maschmann, Adam K. Leroy, Erk Rosolowsky, Leonardo Ubeda, Ashley T. Barnes, Eva Schinnerer, Eric Emsellem, Angus Mok, Kathryn Grasha, Francesca Pinna, Aida Wofford, Ralf S. Klessen, Simon Glover, Sumit K. Sarbadhicary, Ivan Gerasimov. 2026-10-01. Star Cluster Populations in 38 Spiral Galaxies: Evidence for Near-Universal Mass and Age Distributions from PHANGS. https://doi.org/10.3847/1538-4357%2Fae9753

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