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ABSTRACT We use high-resolution Hubble Space Telescope imaging data of dwarf galaxies in the Local Volume ($$\lesssim {11}\, \mathrm{Mpc}$$) to parameterize 19 newly discovered nuclear star clusters (NSCs). Most of the clusters have stellar masses of $$M_{\star }^{\mathrm{nsc}} \lesssim 10^{6}{\, {\rm M}_{\odot }}$$ and compare to Galactic globular clusters in terms of ellipticity, effective radius, stellar mass, and surface density. The clusters are modelled with a Sérsic profile and their surface brightness evaluated at the effective radius reveals a tight positive correlation to the host galaxy stellar mass. Our data also indicate an increase in slope of the density profiles with increasing mass, perhaps indicating an increasing role for in situ star formation in more massive hosts. We evaluate the scaling relation between the clusters and their host galaxy stellar mass to find an environmental dependence: for NSCs in field galaxies, the slope of the relation is $$\alpha = 0.82^{+0.08}_{-0.08}$$ whereas $$\alpha = 0.55^{+0.06}_{-0.05}$$ for dwarfs in the core of the Virgo cluster. Restricting the fit for the cluster to $$M_{\star }^{\mathrm{gal}} \ge 10^{6.5}{\, {\rm M}_{\odot }}$$ yields $$\alpha = 0.70^{+0.08}_{-0.07}$$, in agreement with the field environment within the 1σ interval. The environmental dependence is due to the lowest-mass nucleated galaxies and we speculate that this is either due to an increased number of progenitor globular clusters merging to become an NSC, or due to the formation of more massive globular clusters in dense environments, depending on the initial globular cluster mass function. Our results clearly corroborate recent results in that there exists a tight connection between NSCs and globular clusters in dwarf galaxies.
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An evolutionary continuum from nucleated dwarf galaxies to star clusters
Systematic studies1-4 have revealed hundreds of ultra-compact dwarf galaxies (UCDs5) in the nearby Universe. With half-light radii rh of approximately 10-100 parsecs and stellar masses M* ≈ 106-108 solar masses, UCDs are among the densest known stellar systems6. Although similar in appearance to massive globular clusters7, the detection of extended stellar envelopes4,8,9, complex star formation histories10, elevated mass-to-light ratio11,12 and supermassive black holes13-16 suggest that some UCDs are remnant nuclear star clusters17 of tidally stripped dwarf galaxies18,19, or even ancient compact galaxies20. However, only a few objects have been found in the transient stage of tidal stripping21,22, and this assumed evolutionary path19 has never been fully traced by observations. Here we show that 106 galaxies in the Virgo cluster have morphologies that are intermediate between normal, nucleated dwarf galaxies and single-component UCDs, revealing a continuum that fully maps this morphological transition and fills the `size gap' between star clusters and galaxies. Their spatial distribution and redder colour are also consistent with stripped satellite galaxies on their first few pericentric passages around massive galaxies23. The `ultra-diffuse' tidal features around several of these galaxies directly show how UCDs are forming through tidal stripping and that this evolutionary path can include an early phase as a nucleated ultra-diffuse galaxy24,25. These UCDs represent substantial visible fossil remnants of ancient dwarf galaxies in galaxy clusters, and more low-mass remnants probably remain to be found.
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- PAR ID:
- 10562457
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Nature
- Date Published:
- Journal Name:
- Nature
- Volume:
- 623
- Issue:
- 7986
- ISSN:
- 0028-0836
- Page Range / eLocation ID:
- 296 to 300
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41586-023-06650-z
