An Unexplained Origin for the Unusual Globular Cluster System in the Ultradiffuse Galaxy FCC 224

Publication Date

3-20-2025

Document Type

Article

Publication Title

Astrophysical Journal

Volume

982

Issue

1

DOI

10.3847/1538-4357/adae11

Abstract

We study the quiescent ultradiffuse galaxy FCC 224 in the Fornax cluster using Hubble Space Telescope (HST) imaging, motivated by peculiar properties of its globular cluster (GC) system revealed in shallower imaging. The surface brightness fluctuation distance of FCC 224 measured from HST is 18.6 ± 2.7 Mpc, consistent with the Fornax cluster distance. We use Prospector to infer the stellar population from a combination of multiwavelength photometry (HST, ground-based, Wide-field Infrared Survey Explorer) and Keck Cosmic Web Imager spectroscopy. The galaxy has a mass-weighted age of ∼10 Gyr, metallicity [M/H] of ∼−1.25 dex, and a very short formation e-folding time of τ ∼ 0.3 Gyr. Its 12 candidate GCs exhibit highly homogeneous g475 − I814 colors, merely 0.04 mag bluer than the diffuse starlight, which supports a single-burst formation scenario for this galaxy. We confirm a top-heavy GC luminosity function, similar to the two dark matter deficient galaxies NGC 1052-DF2 and DF4. However, FCC 224 differs from those galaxies with relatively small GC sizes of ∼3 pc (∼35% smaller than typical for other dwarfs), and with radial mass segregation in its GC system. We are not yet able to identify a formation scenario to explain all of the GC properties in FCC 224. Follow-up measurements of the dark matter content in FCC 224 will be crucial because of the mix of similarities and differences among FCC 224, DF2, and DF4.

Funding Number

AST-2308390

Funding Sponsor

W. M. Keck Foundation

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Physics and Astronomy

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