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PHANGS-HST: new methods for star cluster identification in nearby galaxies

We present an innovative and widely applicable approach for the detection and classification of stellar clusters, developed for the PHANGS-HST Treasury Program, an NUV-to-I band imaging campaign of 38 spiral galaxies. Our pipeline first generates a unified master source list for stars and candidate...

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Main Authors: Thilker, David A. (Author) , Whitmore, Bradley C (Author) , Lee, Janice C (Author) , Deger, Sinan (Author) , Chandar, Rupali (Author) , Larson, Kirsten L (Author) , Hannon, Stephen (Author) , Ubeda, Leonardo (Author) , Dale, Daniel A (Author) , Glover, Simon (Author) , Grasha, Kathryn (Author) , Klessen, Ralf S. (Author) , Kruijssen, Diederik (Author) , Rosolowsky, Erik (Author) , Schruba, Andreas (Author) , White, Richard L (Author) , Williams, Thomas G. (Author)
Format: Article (Journal)
Language:English
Published: 2022
In: Monthly notices of the Royal Astronomical Society
Year: 2022, Volume: 509, Issue: 3, Pages: 4094-4127
ISSN:1365-2966
DOI:10.1093/mnras/stab3183
Online Access:Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1093/mnras/stab3183
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Author Notes:David A. Thilker, Bradley C. Whitmore, Janice C. Lee, Sinan Deger, Rupali Chandar, Kirsten L. Larson, Stephen Hannon, Leonardo Ubeda, Daniel A. Dale, Simon C.O. Glover, Kathryn Grasha, Ralf S. Klessen, J.M. Diederik Kruijssen, Erik Rosolowsky, Andreas Schruba, Richard L. White and Thomas G Williams
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Summary:We present an innovative and widely applicable approach for the detection and classification of stellar clusters, developed for the PHANGS-HST Treasury Program, an NUV-to-I band imaging campaign of 38 spiral galaxies. Our pipeline first generates a unified master source list for stars and candidate clusters, to enable a self-consistent inventory of all star formation products. To distinguish cluster candidates from stars, we introduce the Multiple Concentration Index (MCI) parameter, and measure inner and outer MCIs to probe morphology in more detail than with a single, standard concentration index (CI). We improve upon cluster candidate selection, jointly basing our criteria on expectations for MCI derived from synthetic cluster populations and existing cluster catalogues, yielding model and semi-empirical selection regions (respectively). Selection purity (confirmed clusters versus candidates, assessed via human-based classification) is high (up to 70 per cent) for moderately luminous sources in the semi-empirical selection region, and somewhat lower overall (outside the region or fainter). The number of candidates rises steeply with decreasing luminosity, but pipeline-integrated Machine Learning (ML) classification prevents this from being problematic. We quantify the performance of our PHANGS-HST methods in comparison to LEGUS for a sample of four galaxies in common to both surveys, finding overall agreement with 50-75 per cent of human verified star clusters appearing in both catalogues, but also subtle differences attributable to specific choices adopted by each project. The PHANGS-HST ML-classified Class 1 or 2 catalogues reach ∼1 mag fainter, ∼2 × lower stellar mass, and are 2−5 × larger in number, than attained in the human classified samples.
Item Description:Advance access publication 2021 November 11
Gesehen am 25.03.2022
Physical Description:Online Resource
ISSN:1365-2966
DOI:10.1093/mnras/stab3183

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