Major substructure in the M31 outer halo: The south-west cloud

N. F. Bate*, A. R. Conn, B. McMonigal, G. F. Lewis, N. F. Martin, A. W. McConnachie, J. Veljanoski, A. D. Mackey, A. M.N. Ferguson, R. A. Ibata, M. J. Irwin, M. Fardal, A. P. Huxor, A. Babul

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

18 Citations (Scopus)


We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo ofM31. The South-West Cloud lies at a projected distance of ̃100 kpc from the centre of M31 and extends for at least ̃50 kpc in projection. We use Pan-Andromeda Archaeological Survey photometry of red giant branch stars to determine a distance to the South-West Cloud of 793+45-45 kpc. The metallicity of the cloud is found to be [Fe/H] = -1.3 ± 0.1. This is consistent with the coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities determined using an independent technique of [Fe/H] = -1.35 ± 0.15. We measure a brightness for the Cloud of MV = -12.1 mag; this is ̃75 per cent of the luminosity implied by the luminosity-metallicity relation. Under the assumption that the South-West Cloud is the visible remnant of an accreted dwarf satellite, this suggests that the progenitor object was amongst M31's brightest dwarf galaxies prior to disruption.

Original languageEnglish
Pages (from-to)3362-3372
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 1 Feb 2014


  • Galaxies
  • Individual
  • M31-Local Group-galaxies
  • Stellar content.

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