Rediscovery of the Sixth Star Cluster in the Fornax Dwarf Spheroidal Galaxy

Abstract

Since first noticed by Shapley in 1939, a faint object coincident with the Fornax dwarf spheroidal has long been discussed as a possible sixth globular cluster system. However, debate has continued over whether this overdensity is a statistical artifact or a blended galaxy group. In this Letter we demonstrate, using deep DECam imaging data, that this object is well resolved into stars and is a bona fide star cluster. The stellar overdensity of this cluster is statistically significant at the level of ~ 6 - 6.7 sigma in several different photometric catalogs including Gaia. Therefore, it is highly unlikely to be caused by random fluctuation. We show that Fornax 6 is a star cluster with a peculiarly low surface brightness and irregular shape, which may indicate a strong tidal influence from its host galaxy. The Hess diagram of Fornax 6 is largely consistent with that of Fornax field stars, but it appears to be slightly bluer. However, it is still likely more metal-rich than most of the globular clusters in the system. Faint clusters like Fornax 6 that orbit and potentially get disrupted in the centers of dwarf galaxies can prove crucial for constraining the dark matter distribution in Milky Way satellites.

6 pages, 4 figures, 1 table, submitted to ApJL

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Cited by in corpus (17)

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• A dwarf-dwarf merger and dark matter core as a solution to the Globular Cluster problems in the Fornax dSph
• A Photometric Survey of Globular Cluster Systems in Brightest Cluster Galaxies
• Search for globular clusters associated with the Milky Way dwarf galaxies using Gaia DR2
• Assessing the Fornax globular cluster timing problem in different models of dark matter
• Spectroscopic Confirmation of the Sixth Globular Cluster in the Fornax Dwarf Spheroidal Galaxy
• Density Wakes due to Dynamical Friction in Cored Potentials
• The survival of globular clusters in a cuspy Fornax
• $S^5$: The destruction of a bright dwarf galaxy as revealed by the chemistry of the Indus stellar stream
• Dynamical friction in Bose-Einstein condensed self-interacting dark matter at finite temperatures, and the Fornax dwarf spheroidal
• No globular cluster progenitors in Milky Way satellite galaxies
• Is Fornax 4 the nuclear star cluster of the Fornax dwarf spheroidal galaxy?
• The secular evolution of a uniform density star cluster immersed in a compressible galactic tidal field
• Tidal mass loss in the Fornax dwarf spheroidal galaxy through N-body simulations with Gaia DR3-based orbits
• APOGEE chemical abundances of stars in the MW satellites Fornax, Sextans, Draco and Carina