The distribution of gas in the local group from constrained cosmological simulations: The case for andromeda and the milky way galaxies

Abstract

We study the gas distribution in the Milky Way and Andromeda using a constrained cosmological simulation of the Local Group (LG) within the context of the CLUES (Constrained Local UniversE Simulations) project. We analyse the properties of gas in the simulated galaxies at z = 0 for three different phases: 'cold', 'hot' and HI, and compare our results with observations. The amount of material in the hot halo (Mhot ≈ 4-5 × 1010M⊙), and the cold (Mcold(r ≲ 10 kpc) ≈ 108M⊙) and HI (MHI(r ≲ 50 kpc) ≈ 3-4 × 108M⊙) components displays reasonable agreement with observations. We also compute the accretion/ejection rates together with the HI (radial and all-sky) covering fractions. The integrated HI accretion rate within r = 50 kpc gives ~0.2-0.3M⊙ yr-1, i.e. close to that obtained from high-velocity clouds in the Milky Way. We find that the global accretion rate is dominated by hot material, although ionized gas with T ≲ 105 K can contribute significantly too. The net accretion rates of all material at the virial radii are 6-8M⊙ yr-1. At z = 0, we find a significant gas excess between the two galaxies, as compared to any other direction, resulting from the overlap of their gaseous haloes. In our simulation, the gas excess first occurs at z ~ 1, as a result of the kinematical evolution of the LG. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.