CASS BlogHierarchical structure in the Pan-Andromeda Archaeological Survey
01/02/19 20:38 Filed in: Science
The Pan-Andromeda Archaeological Survey (McConnachie et al. 2018) is a survey of 400 square degrees centered on the Andromeda (M31) and Triangulum (M33) galaxies. A dozen of distinctive substructures were detected and produced by at least 5 different accretion events, all in the last 3 or 4 Gyrs. A few of the substructures furthest from M31 may be shells from a single accretion event. M31’s halo seems to be dominated by two "mega-structures" that can be considered as the two most significant branches of a merger tree produced by breaking M31’s stellar halo into smaller and smaller structures. One of the streams could in fact be associated primarily with M33’s halo. The CASS hyper-spectral data cubes will contribute to understanding the formation of the Pan-Andromeda system.
Tangent plane projection centered on M31 showing the spatial density distribution of candidate red giant branch stars. The dashed circles correspond to projected radii of 50kpc, 100kpc and 150kpc from M31, and 50 kpc from M33 (Figure 11 in McConnachie et al. 2018).
Tangent plane projection centered on M31 with the positions of all major stellar substructures, globular clusters and dwarf galaxies highlighted (Figure 12 in McConnachie et al. 2018).
Tangent plane projection centered on M31 showing the spatial density distribution of candidate red giant branch stars. The dashed circles correspond to projected radii of 50kpc, 100kpc and 150kpc from M31, and 50 kpc from M33 (Figure 11 in McConnachie et al. 2018).
Tangent plane projection centered on M31 with the positions of all major stellar substructures, globular clusters and dwarf galaxies highlighted (Figure 12 in McConnachie et al. 2018).