Puzzling Outer-Density Profile of the Dark Matter Halo in the Andromeda Galaxy

Abstract

The cold dark matter (CDM) cosmology, which is the standard theory of the structure formation in the universe, predicts that the outer density profile of dark matter halos decreases with the cube of distance from the center. However, so far not much effort has examined this hypothesis. In the halo of the Andromeda galaxy (M31), large-scale stellar structures detected by the recent observations provide a potentially suitable window to investigate the mass--density distribution of the dark matter halo. We explore the density structure of the dark matter halo in M31 using an N-body simulation of the interaction between an accreting satellite galaxy and M31. To reproduce the Andromeda Giant Southern Stream and the stellar shells at the east and west sides of M31, we find the sufficient condition for the power-law index $\alpha$ of the outer density distribution of the dark matter halo. The best-fit parameter is $\alpha =-3.7$, which is steeper than the CDM prediction.

arXiv comment5 pages, 4 figures, accepted for publication in PASJ Letter

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Cited by in corpus (11)

• A 2-3 billion year old major merger paradigm for the Andromeda galaxy and its outskirts
• On feathers, bifurcations and shells: the dynamics of tidal streams across the mass scale
• Elemental Abundances in M31: First Alpha and Iron Abundance Measurements in M31's Giant Stellar Stream
• Formation of the Andromeda Giant Stream: Asymmetric Structure and Disc Progenitor
• Elemental Abundances in M31: Gradients in the Giant Stellar Stream
• Collision tomography: Physical properties of possible progenitors of the Andromeda stellar stream
• Kinematics and Metallicity of Red Giant Branch Stars in the Northeast Shelf of M31
• The nature of the progenitor of the M31 North-western stream: globular clusters as milestones of its orbit
• The survey of planetary nebulae in Andromeda (M31) VII. Predictions of a major merger simulation model compared with chemodynamical data of the disc and inner halo substructures
• Prospects for annihilating dark matter from M31 and M33 observations with the Cherenkov Telescope Array
• The origin of the black hole offset in M31