The outer halo globular cluster system of M31 - III. Relationship to the stellar halo

A. D. Mackey*, A. M. N. Ferguson, A. P. Huxor, J. Veljanoski, G. F. Lewis, A. W. McConnachie, N. F. Martin, R. A. Ibata, M. J. Irwin, P. Côté, M. L. M. Collins, N. R. Tanvir, N. F. Bate

*Corresponding author for this work

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Abstract

We utilize the final catalogue from the Pan-Andromeda Archaeological Survey to investigate the links between the globular cluster system and field halo in M31 at projected radii Rproj = 25-150 kpc. In this region the cluster radial density profile exhibits a power-law decline with index Γ = -2.37 ± 0.17, matching that for the stellar halo component with [Fe/H] < -1.1. Spatial density maps reveal a striking correspondence between the most luminous substructures in the metal-poor field halo and the positions of many globular clusters. By comparing the density of metal-poor halo stars local to each cluster with the azimuthal distribution at commensurate radius, we reject the possibility of no correlation between clusters and field overdensities at 99.95{{ per cent}} significance. We use our stellar density measurements and previous kinematic data to demonstrate that ≈ 35-60 per cent of clusters exhibit properties consistent with having been accreted into the outskirts of M31 at late times with their parent dwarfs. Conversely, at least {̃ }40{{ per cent}} of remote clusters show no evidence for a link with halo substructure. The radial density profile for this subgroup is featureless and closely mirrors that observed for the apparently smooth component of the metal-poor stellar halo. We speculate that these clusters are associated with the smooth halo; if so, their properties appear consistent with a scenario where the smooth halo was built up at early times via the destruction of primitive satellites. In this picture the entire M31 globular cluster system outside Rproj = 25 kpc comprises objects accumulated from external galaxies over a Hubble time of growth.
Original languageEnglish
Pages (from-to)1756-1789
Number of pages34
JournalMonthly Notices of the Royal Astronomical Society
Volume484
Issue number2
DOIs
Publication statusPublished - 1-Apr-2019

Keywords

  • globular clusters: general
  • galaxies: formation
  • galaxies: haloes
  • galaxies: individual (M31)
  • Local Group
  • TRACING GALAXY FORMATION
  • GIANT SOUTHERN STREAM
  • NEARBY DWARF GALAXIES
  • MASS BLACK-HOLE
  • MILKY-WAY
  • ANDROMEDA GALAXY
  • STAR-CLUSTERS
  • LOCAL GROUP
  • ACCRETION ORIGIN
  • NGC 147

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