How baryons affect haloes and large-scale structure: a unified picture from the Simba simulation

Using the state-of-the-art suite of hydrodynamic simulations Simba, as well as its dark-matter-only counterpart, we study the impact of the presence of baryons and of different stellar/AGN feedback mechanisms on large-scale structure, halo density profiles, and on the abundance of different baryonic phases within haloes and in the intergalactic medium (IGM). The unified picture that emerges from our analysis is that the main physical drivers shaping the distribution of matter at all scales are star formation-driven galactic outflows at z > 2 for lower mass haloes and AGN jets at z < 2 in higher mass haloes. Feedback suppresses the baryon mass function with time relative to the halo mass function, and it even impacts the halo mass function itself at the similar to 20 per cent level, particularly evacuating the centres and enhancing dark matter just outside haloes. At early epochs baryons pile up in the centres of haloes, but by late epochs and particularly in massive systems gas has mostly been evacuated from within the inner halo. AGN jets are so efficient at such evacuation that at low redshifts the baryon fraction within similar to 10(12)-10(13) M-circle dot haloes is only 25 per cent of the cosmic baryon fraction, mostly in stars. The baryon fraction enclosed in a sphere around such haloes approaches the cosmic value omega(b)/omega(m) only at 10-20 virial radii. As a result, 87 per cent of the baryonic mass in the Universe lies in the IGM at z = 0, with 67 per cent being in the form of warm-hot IGM (T > 10(5)K).

Automated summary

The study indicates that star formation in galaxies and AGN jets have significant impacts on the distribution of matter, especially causing baryon evacuation at different redshifts. In larger systems, AGN jets are particularly efficient in evacuating baryons, leading to the majority of baryonic mass being in the IGM.