Young accreted globular clusters in the outer halo of M31

Abstract

We report on Gemini/GMOS observations of two newly discovered globular clusters in the outskirts of M31. These objects, PAndAS-7 and PAndAS-8, lie at a galactocentric radius of ~87 kpc and are projected, with separation ~19 kpc, onto a field halo substructure known as the South-West Cloud. We measure radial velocities for the two clusters which confirm that they are almost certainly physically associated with this feature. Colour-magnitude diagrams reveal strikingly short, exclusively red horizontal branches in both PA-7 and PA-8; both also have photometric [Fe/H] = -1.35 +/- 0.15. At this metallicity, the morphology of the horizontal branch is maximally sensitive to age, and we use the distinctive configurations seen in PA-7 and PA-8 to demonstrate that both objects are very likely to be at least 2 Gyr younger than the oldest Milky Way globular clusters. Our observations provide strong evidence for young globular clusters being accreted into the remote outer regions of M31 in a manner entirely consistent with the established picture for the Milky Way, and add credence to the idea that similar processes play a central role in determining the composition of globular cluster systems in large spiral galaxies in general.

14 pages, 8 figures, accepted for publication in MNRAS

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Cited by in corpus (37)

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• Globular Cluster Formation and Evolution in the Context of Cosmological Galaxy Assembly: Open Questions
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• The outer halo globular cluster system of M31 - II. Kinematics
• Gas expulsion in massive star clusters? Constraints from observations of young and gas-free objects
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• Kinematics of Outer Halo Globular Clusters in M31
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• The Detailed Chemical Properties of M31 Star Clusters I. Fe, Alpha and Light Elements
• Star Clusters in M31: VII. Global Kinematics and Metallicity Subpopulations of the Globular Clusters
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• The difference in metallicity distribution functions of halo stars and globular clusters as a function of galaxy type: A tracer of globular cluster formation and evolution
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• Major Substructure in the M31 Outer Halo: the South-West Cloud
• The southern leading and trailing wraps of the Sagittarius tidal stream around the globular cluster Whiting1
• Accretion in action: phase space coherence of stellar debris and globular clusters in Andromeda's South-West Cloud
• Globular Cluster Systems of Relic Galaxies
• Kinematics of a globular cluster with an extended profile: NGC5694
• Euclid preparation. LVIII. Detecting globular clusters in the Euclid survey
• Major Substructure in the M31 Outer Halo: the East Cloud
• No sign (yet) of intergalactic globular clusters in the Local Group
• Hubble Space Telescope imaging of the extremely metal-poor globular cluster EXT8 in Messier 31
• Metallicities of Outer Halo M31 Globular Clusters from Integrated Light Calcium-II Triplet Spectroscopy
• A Dwarf Disrupting -- Andromeda XXVII and the North West Stream
• The nature of the Eastern Extent in the outer halo of M31
• Chemical Abundances of Seven Outer Halo M31 Globular Clusters from the Pan-Andromeda Archaeological Survey
• Properties of the Lower Segment of M31's North West Stream