Major Substructure in the M31 Outer Halo: the East Cloud

Abstract

We present the first detailed analysis of the East Cloud, a highly disrupted diffuse stellar substructure in the outer halo of M31. The core of the substructure lies at a projected distance of $\sim 100$ kpc from the centre of M31 in the outer halo, with possible extensions reaching right into the inner halo. Using Pan-Andromeda Archaeological Survey photometry of red giant branch stars, we measure the distance, metallicity and brightness of the cloud. Using Hubble Space Telescope data, we independently measure the distance and metallicity to the two globular clusters coincident with the East Cloud core, PA-57 and PA-58, and find their distances to be consistent with the cloud. Four further globular clusters coincident with the substructure extensions are identified as potentially associated. Combining the analyses, we determine a distance to the cloud of $814_{-9}^{+20}$ kpc, a metallicity of $[Fe/H]=-1.2\pm 0.1$, and a brightness of $M_V=-10.7\pm 0.4$ mag. Even allowing for the inclusion of the potential extensions, this accounts for less than $20$ per cent of the progenitor luminosity implied by the luminosity-metallicity relation. Using the updated techniques developed for this analysis, we also refine our estimates of the distance and brightness of the South-West Cloud, a separate substructure analyzed in the previous work in this series.

14 pages, 11 figures, 5 tables

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Cited by in corpus (11)

• The large-scale structure of the halo of the Andromeda galaxy II. Hierarchical structure in the Pan-Andromeda Archaeological Survey
• The outer halo globular cluster system of M31 - III. Relationship to the stellar halo
• Fermi-LAT Observations of Gamma-Ray Emission Towards the Outer Halo of M31
• Major Substructure in the M31 Outer Halo: Distances and Metallicities along the Giant Stellar Stream
• A spectroscopic study of blue supergiant stars in Local Group spiral galaxies: Andromeda and Triangulum
• Asymmetric Drift in the Andromeda Galaxy (M31) as a Function of Stellar Age
• A panoramic view of the Local Group dwarf galaxy NGC 6822
• Metallicities of Outer Halo M31 Globular Clusters from Integrated Light Calcium-II Triplet Spectroscopy
• Simulations of the accreted stellar halos of low-mass field galaxies
• Integrated Spectroscopy of Extragalactic Globular Clusters
• Chemical Abundances of Seven Outer Halo M31 Globular Clusters from the Pan-Andromeda Archaeological Survey