The PAndAS View of the Andromeda Satellite System. IV. Global Properties

Abstract

We build a statistical framework to infer the global properties of the satellite system of the Andromeda galaxy (M31) from the properties of individual dwarf galaxies located in the Pan-Andromeda Archaelogical Survey (PAndAS) and the previously determined completeness of the survey. Using forward modeling, we infer the slope of the luminosity function of the satellite system, the slope of its spatial density distribution, and the size–luminosity relation followed by the dwarf galaxies. We find that the slope of the luminosity function is β = −1.5 ± 0.1. Combined with the spatial density profile, it implies that, when accounting for survey incompleteness, M31 hosts ${92}_{-26}^{+19}$ dwarf galaxies with M _V 99.9% confidence and conclude that this anisotropy is an intrinsic feature of the M31 satellite system. The statistical framework we present here is a powerful tool to robustly constrain the properties of a satellite system and compare those across hosts, especially considering the upcoming start of the Euclid or Rubin large photometric surveys that are expected to uncover a large number of dwarf galaxies in the Local Volume.

Keywords

• Andromeda Galaxy
• Dwarf galaxies
• Local Group