Major substructure in the M31 outer halo: Distances and metallicities along the giant stellar stream

Anthony Conn, B. McMonigal, N. F. Bate, G. F. Lewis, Rodrigo A. Ibata, N. F. Martin, A. W. McConnachie, A. M N Ferguson, M.J. Irwin, P. J. Elahi, K. A. Venn, A. D. Mackey

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Abstract

We present a renewed look at M31's giant stellar stream along with the nearby structures streams C and D, exploiting a new algorithm capable of fitting to the red giant branch (RGB) of a structure in both colour and magnitude space. Using this algorithm, we are able to generate probability distributions in distance, metallicity and RGB width for a series of subfields spanning these structures. Specifically, we confirm a distance gradient of approximately 20 kpc per degree along a 6 deg extension of the giant stellar stream, with the farthest subfields from M31 lying ~120 kpc more distant than the innermost subfields. Further, we find a metallicity that steadily increases from-0.7-0.1 +0.1 to-0.2-0.1 +0.2 dex along the inner half of the stream before steadily dropping to a value of-1.0-0.2 +0.2 dex at the farthest reaches of our coverage. The RGB width is found to increase rapidly from 0.4-0.1 +0.1 to 1.1-0.1 +0.2 dex in the inner portion of the stream before plateauing and decreasing marginally in the outer subfields of the stream. In addition, we estimate stream C to lie at a distance between 794 and 862 kpc and stream D between 758 and 868 kpc. We estimate the median metallicity of stream C to lie in the range-0.7 to-1.6 dex and a metallicity of-1.1-0.2 +0.3 dex for stream D. RGB widths for the two structures are estimated to lie in the range 0.4-1.2 dex and 0.3-0.7 dex, respectively. In total, measurements are obtained for 19 subfields along the giant stellar stream, four along stream C, five along stream D and three general M31 spheroid fields for comparison. We thus provide a higher resolution coverage of the structures in these parameters than has previously been available in the literature.

Original languageEnglish
Pages (from-to)3282-3298
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume458
Issue number3
DOIs
Publication statusPublished - 8 Mar 2016
Externally publishedYes

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Conn, A., McMonigal, B., Bate, N. F., Lewis, G. F., Ibata, R. A., Martin, N. F., ... Mackey, A. D. (2016). Major substructure in the M31 outer halo: Distances and metallicities along the giant stellar stream. Monthly Notices of the Royal Astronomical Society, 458(3), 3282-3298. https://doi.org/10.1093/mnras/stw513