M31 (nomenclature structures in the outer halo of the galaxy)
Andromeda [Ultra Deep 2019]
Credit: Giuseppe Donatiello
This utra-deep image version of Andromeda offers a good overview the main structures on the disc and shape of the weak structures present in the outer halo of Andromeda (M31).
The galaxy disc appears quite regular and there is an abundant presence of young stars, gases and abundant dusts. Bulge is dominated by an older population. The external halo presents various irregularities and thickenings that we can consider as vestiges of dwarf galaxies incorporated progressively by the greater galaxy, as foreseen by the growth models.
M31 is thought to have assimilated a few hundred small galaxies or globular clusters. This process is still ongoing.
According to Ferguson et al. (2002), the names attributed to the various substructures, unknown to most, are reported in the negative image with disc color inset.
More about:
https://iopscience.iop.org/article/10.1086/342019/fulltext/202181.text.html
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