CaltechAUTHORS
Published March 2023 | Version Published + Supplemental Material
Journal Article Open

Improving Star Cluster Age Estimates in PHANGS-HST Galaxies and the Impact on Cluster Demographics in NGC 628

Creators

  • 1. ROR icon Space Telescope Science Institute
  • 2. ROR icon University of Toledo
  • 3. ROR icon NOIRLab
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon University of Wyoming
  • 6. ROR icon University of Arizona
  • 7. ROR icon Johns Hopkins University
  • 8. ROR icon University of Antofagasta
  • 9. ROR icon Heidelberg University
  • 10. ROR icon University of Bonn
  • 11. ROR icon European Southern Observatory
  • 12. ROR icon Australian National University
  • 13. ROR icon International Centre for Radio Astronomy Research
  • 14. ROR icon University of California, Riverside
  • 15. ROR icon The Ohio State University
  • 16. ROR icon Ontario College of Art and Design
  • 17. ROR icon Tamkang University
  • 18. ROR icon Max Planck Institute for Astronomy
  • 19. ROR icon Complutense University of Madrid

Abstract

A long-standing problem when deriving the physical properties of stellar populations is the degeneracy between age, reddening, and metallicity. When a single metallicity is used for all the star clusters in a galaxy, this degeneracy can result in 'catastrophic' errors for old globular clusters. Typically, approximately 10–20 per cent of all clusters detected in spiral galaxies can have ages that are incorrect by a factor of 10 or more. In this paper, we present a pilot study for four galaxies (NGC 628, NGC 1433, NGC 1365, and NGC 3351) from the PHANGS-HST survey. We describe methods to correct the age-dating for old globular clusters, by first identifying candidates using their colours, and then reassigning ages and reddening based on a lower metallicity solution. We find that young 'Interlopers' can be identified from their Hα flux. CO (2-1) intensity or the presence of dust can also be used, but our tests show that they do not work as well. Improvements in the success fraction are possible at the ≈15 per cent level (reducing the fraction of catastrophic age-estimates from between 13 and 21 per cent, to between 3  and 8 per cent). A large fraction of the incorrectly age-dated globular clusters are systematically given ages around 100 Myr, polluting the younger populations as well. Incorrectly age-dated globular clusters significantly impact the observed cluster age distribution in NGC 628, which affects the physical interpretation of cluster disruption in this galaxy. For NGC 1365, we also demonstrate how to fix a second major age-dating problem, where very dusty young clusters with E(B − V) > 1.5 mag are assigned old, globular-cluster like ages. Finally, we note the discovery of a dense population of ≈300 Myr clusters around the central region of NGC 1365 and discuss how this results naturally from the dynamics in a barred galaxy.

Additional Information

© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). We thank the referee for several useful and constructive comments that lead to improvements in the paper. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Support for Program number 15654 was provided through a grant from the STScI under NASA contract NAS5-26555. FB and AB would like to acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 726384/Empire). MB gratefully acknowledges support by the ANID BASAL project FB210003 and from the FONDECYT regular grant 1211000. EW acknowledges support from the DFG via SFB 881 'The Milky Way System' (project-ID 138713538; subproject P01). FB acknowledges funding from the ERC under the European Union's Horizon 2020 research and innovation programme (grant agreement No.726384/Empire). HAP acknowledges support by the National Science and Technology Council of Taiwan under grant 110-2112-M-032-020-MY3. JMDK acknowledges funding from the ERC under the European Union's Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). COOL Research DAO is a Decentralized Autonomous Organization supporting research in astrophysics aimed at uncovering our cosmic origins. KG is supported by the Australian Research Council through the Discovery Early Career Researcher Award (DECRA) Fellowship DE220100766 funded by the Australian Government. KK and FS gratefully acknowledge funding from the German Research Foundation (DFG) in the form of an Emmy Noether Research Group (grant No. KR4598/2-1, PI Kreckel). PSB acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities under grant number PID2019-107427GB-C31. RSK and MCS are thankful for support from the Deutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center (SFB 881, Project-ID 138713538) 'The Milky Way System' (sub-projects A1, B1, B2 and B8) and from the Heidelberg Cluster of Excellence (EXC 2181 - 390900948) 'STRUCTURES: A unifying approach to emergent phenomena in the physical world, mathematics, and complex data', funded by the German Excellence Strategy. RSK and MSC also acknowledge funding from the ERC in the ERC Synergy Grant 'ECOGAL – Understanding our Galactic ecosystem: From the disc of the Milky Way to the formation sites of stars and planets' (project ID 855130). TGW acknowledges funding from the ERC under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 694343). DATA AVAILABILITY. The imaging observations underlying this article can be retrieved from the Mikulski Archive for Space Telescopes at https://archive.stsci.edu/hst/search_retrieve.html under proposal GO-15654. High level science products, including science ready mosaicked imaging, associated with HST GO-15654 are provided at https://archive.stsci.edu/hlsp/phangs-hst with digital object identifier doi: 10.17909/t9-r08f-dq31

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Additional details

Identifiers

Eprint ID
120266
Resolver ID
CaltechAUTHORS:20230321-821389800.62

Funding

NASA
NAS 5-26555
European Research Council (ERC)
726384
Agencia Nacional de Investigación y Desarrollo (ANID)
FB210003
Fondo Nacional de Desarrollo Científíco y Tecnológico (FONDECYT)
1211000
Deutsche Forschungsgemeinschaft (DFG)
138713538 - SFB 881
Ministry of Science and Technology (Taipei)
110-2112-M-032-020-MY3
European Research Council (ERC)
714907
Australian Research Council
DE220100766
Deutsche Forschungsgemeinschaft (DFG)
KR4598/2-1
Ministerio de Ciencia, Innovación y Universidades (MICIU)
PID2019-107427GB-C31
Deutsche Forschungsgemeinschaft (DFG)
EXC 2181 - 390900948
European Research Council (ERC)
855130
European Research Council (ERC)
694343

Dates

Created
2023-05-17
Created from EPrint's datestamp field
Updated
2023-05-17
Created from EPrint's last_modified field

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