Bimodal gas accretion in the Horizon-MareNostrum galaxy formation simulation

Understand

(abridged) The physics of diffuse gas accretion and the properties of the cold and hot modes of accretion onto proto-galaxies between z=2 and z=5.4 is investigated using the large cosmological simulation performed with the RAMSES code on the MareNostrum supercomputing facility.

• Galactic winds, chemical enrichment, UV background heating and radiative cooling are taken into account in this very high resolution simulation.
• Using accretion--weighted temperature histograms, we have perfomed two different measurements of the thermal state of the gas accreted towards the central galaxy.
• The first measurement, performed using accretion--weighted histograms on a spherical surface of radius 0.2 Rvir centred on the densest gas structure near the halo centre of mass, is a good indicator of the presence of an accretion shock in the vicinity of the galactic disc.