Evolution of the baryon fraction in the Local Group: accretion versus feedback at low and high z

Understand

Using hydrodynamical zoom simulations in the standard LCDM cosmology, we investigate the evolution of the distribution of baryons (gas and stars) in a local group-type universe.

• First, with standard star formation and supernova feedback prescriptions, we find that the mean baryonic fraction value estimated at the virial radius of the two main central objects (i.e.
• the Milky Way and Andromeda) is decreasing over time, and is 10-15% lower than the universal value, 0.166, at z=0.
• This decrease is mainly due to the fact that the amount of accretion of dissipative gas onto the halo, especially at low redshift, is in general much lower than that of the dissipationless dark matter.