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arXiv · 1311.0906

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
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Abstract

We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo of M31. 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 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 M_V = -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.

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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. 2013-11-04. Major Substructure in the M31 Outer Halo: the South-West Cloud. https://doi.org/10.1093/mnras%2Fstt2139

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