PHANGS-HST Catalogs for ∼100,000 Star Clusters and Compact Associations in 38 Galaxies. II. Physical Properties from Decision-tree-based Spectral Energy Distribution Fitting of NUV-<i>U</i>-<i>B</i>-<i>V</i> <i>-</i> <i>I</i> Photometry with Categori

Abstract This paper is the second in a series presenting the catalogs and properties of the largest sample to date of ∼100,000 star clusters and compact associations, in 38 spiral galaxies observed by the PHANGS-HST Treasury survey. Here, we present spectral energy distribution (SED) fitting techniques used to compute the age, mass, and reddening for each object. Our decision-tree-based strategy incorporates categorical priors on model age, reddening, and metallicity determined from additional observed parameters: localized H α emission, source morphology, and demographic-specific locations in the UBVI color–color diagram. This approach is implemented to mitigate model degeneracies, particularly between young dusty clusters and old clusters with minimal dust, which can have identical optical colors. Results based on H α narrowband imaging from the ground and from Hubble Space Telescope are intercompared, and contrasted with previous SED-fitting efforts. The fraction of the population that is subject to such priors is ∼14%, and of this subset, ∼63% of old globular clusters (GCs) have ages that change by a factor of 10 or more relative to unconstrained fits with single metallicity ( Z ⊙ ) simple stellar population models. The demographics of the population are examined through age–mass and age–reddening diagrams (for individual galaxies as well as aggregated over the sample), and the GC mass function. We demonstrate relationships between cluster age–mass diagrams and properties of parent galaxies (galaxy morphology and location relative to the galaxy main sequence). We outline continuing efforts to improve the inference of physical properties, including the incorporation of JWST infrared photometry and updated synthesis models.

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Publication Details

Journal
The Astrophysical Journal Supplement Series
Published
2025-08-11
DOI
https://doi.org/10.3847/1538-4365/addabb
Citations
3
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
3.46

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article

PHANGS-HST Catalogs for ∼100,000 Star Clusters and Compact Associations in 38 Galaxies. II. Physical Properties from Decision-tree-based Spectral Energy Distribution Fitting of NUV-U-B-V - I Photometry with Categori

Kiana F. Henny, Justus Neumann, David A. Thilker, M. Boquien et al.
3 citations
The Astrophysical Journal Supplement Series
Galaxies: Formation, Evolution, Phenomena
3.46
article

PHANGS-HST Catalogs for ∼100,000 Star Clusters and Compact Associations in 38 Galaxies. II. Physical Properties from Decision-tree-based Spectral Energy Distribution Fitting of NUV-U-B-V - I Photometry with Categori

Kiana F. Henny, Justus Neumann, David A. Thilker, M. Boquien, Aida Wofford, Francesco Belfiore, Erik Rosolowsky, Francesca Pinna, Daniel Maschmann, Ashley T. Barnes, Frank Bigiel, Thomas G. Williams, Kathryn Grasha, Brent A Groves, Eva Schinnerer, Sinan Deger, Bradley C. Whitmore, Alessandro Razza, Ralf S. Klessen, Hwihyun Kim, Rupali Chandar, Leonardo Úbeda, Daniel A. Dale, M. Jimena Rodríguez, Janice Lee
article en
3 citations

Abstract

Abstract This paper is the second in a series presenting the catalogs and properties of the largest sample to date of ∼100,000 star clusters and compact associations, in 38 spiral galaxies observed by the PHANGS-HST Treasury survey. Here, we present spectral energy distribution (SED) fitting techniques used to compute the age, mass, and reddening for each object. Our decision-tree-based strategy incorporates categorical priors on model age, reddening, and metallicity determined from additional observed parameters: localized H α emission, source morphology, and demographic-specific locations in the UBVI color–color diagram. This approach is implemented to mitigate model degeneracies, particularly between young dusty clusters and old clusters with minimal dust, which can have identical optical colors. Results based on H α narrowband imaging from the ground and from Hubble Space Telescope are intercompared, and contrasted with previous SED-fitting efforts. The fraction of the population that is subject to such priors is ∼14%, and of this subset, ∼63% of old globular clusters (GCs) have ages that change by a factor of 10 or more relative to unconstrained fits with single metallicity ( Z ⊙ ) simple stellar population models. The demographics of the population are examined through age–mass and age–reddening diagrams (for individual galaxies as well as aggregated over the sample), and the GC mass function. We demonstrate relationships between cluster age–mass diagrams and properties of parent galaxies (galaxy morphology and location relative to the galaxy main sequence). We outline continuing efforts to improve the inference of physical properties, including the incorporation of JWST infrared photometry and updated synthesis models.

The Astrophysical Journal Supplement SeriesVol. 280(1)
Australian National University (AU), University of Wyoming (US), Centre National de la Recherche Scientifique (FR), Space Telescope Science Institute (US), European Southern Observatory (DE), University of Bonn (DE), University of Arizona (US), Johns Hopkins University (US), University of Alberta (CA), Universidad de La Laguna (ES), Universidad Autónoma de Baja California (MX), The University of Western Australia (AU), Université Côte d'Azur (FR), Heidelberg University (DE), University of Cambridge (GB), Arcetri Astrophysical Observatory (IT), Ensenada Institute of Technology (MX), University of California San Diego (US), University of Oxford (GB), ASTRO-3D (AU), Gemini North Observatory (US), Max Planck Institute for Astronomy (DE), Université Bourgogne Franche-Comté (FR), Observatoire de la Côte d’Azur (FR), Instituto de Astrofísica de Canarias (ES), NSF NOIRLab (US), ARC Centre of Excellence for All-sky Astrophysics (AU), International Centre for Radio Astronomy Research (AU), University of Chile (CL), Universidad Nacional Autónoma de México (MX), University of Toledo (US)
Space Telescope Science Institute
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Galaxies: Formation, Evolution, Phenomena
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