Diversity of nuclear star cluster formation mechanisms revealed by their star formation histories

K. Fahrion*, M. Lyubenova, G. van de Ven, M. Hilker, R. Leaman, J. Falcón-Barroso, A. Bittner, L. Coccato, E. M. Corsini, D. A. Gadotti, E. Iodice, R. M. McDermid, I. Martín-Navarro, F. Pinna, A. Poci, M. Sarzi, P. T. de Zeeuw, L. Zhu

*Corresponding author for this work

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Abstract

Nuclear star clusters (NSCs) are the densest stellar systems in the Universe and are found in the centres of all types of galaxies. They are thought to form via mergers of star clusters such as ancient globular clusters (GCs) that spiral to the centre as a result of dynamical friction or through in situ star formation directly at the galaxy centre. There is evidence that both paths occur, but the relative contribution of either channel and their correlation with galaxy properties are not yet constrained observationally. Our aim was to derive the dominant NSC formation channel for a sample of 25 nucleated galaxies, mostly in the Fornax galaxy cluster, with stellar masses between Mgal ∼ 108 and 1010.5 M and NSC masses between MNSC ∼ 105 and 108.5 M. Using Multi-Unit Spectroscopic Explorer data from the Fornax 3D survey and the ESO archive, we derived star formation histories, mean ages, and metallicities of NSCs, and compared them to the host galaxies. In many low-mass galaxies, the NSCs are significantly more metal poor than their hosts, with properties similar to GCs. In contrast, in the massive galaxies we find diverse star formation histories and cases of ongoing or recent in situ star formation. Massive NSCs (> 107 M ) occupy a different region in the mass-metallicity diagram than lower-mass NSCs and GCs, indicating a different enrichment history. We find a clear transition of the dominant NSC formation channel with both galaxy and NSC mass. We hypothesise that while GC accretion forms the NSCs of the dwarf galaxies, central star formation is responsible for the efficient mass build up in the most massive NSCs in our sample. At intermediate masses both channels can contribute. The transition between these formation channels seems to occur at galaxy masses Mgal ∼ 109 M and NSC masses MNSC ∼ 107  M .

Original languageEnglish
Article numberA137
Pages (from-to)1-18
Number of pages18
JournalAstronomy and Astrophysics
Volume650
DOIs
Publication statusPublished - 22 Jun 2021

Bibliographical note

Reproduced with permission from Astronomy & Astrophysics, Copyright ESO 2021. First published in Astronomy and Astrophysics, 650, A137, 2021, published by EDP Sciences. The original publication is available at https://doi.org/10.1051/0004-6361/202140644. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • Galaxies: clusters: individual: Fornax
  • Galaxies: nuclei
  • Galaxies: star clusters: general

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