Daniele Sorini

We use the simba galaxy formation simulation suite to explore anisotropies in the properties of circumgalactic gas that result from accretion and feedback processes. We particularly focus on the impact of bipolar active galactic nuclei (AGNs) jet feedback as implemented in simba , which quenches galaxies and has a dramatic effect on large-scale gas properties. We show that jet feedback at low redshifts is most common in the stellar mass range (1–5) × 1010 M⊙, so we focus on galaxies with active jets in this mass range. In comparison to runs without jet feedback, jets cause lower densities and higher temperatures along the galaxy minor axis (simba jet direction) at radii $\gtrsim 0.5r_{200c}-4r_{200c}$ and beyond. This effect is less apparent at higher or lower stellar masses, and is strongest within green valley galaxies. The metallicity also shows strong anisotropy out to large scales, driven by star formation feedback. We find substantially stronger anisotropy at $\lesssim 0.5r_{200c}$, but this also exists in runs with no explicit feedback, suggesting that it is due to anisotropic accretion. Finally, we explore anisotropy in the bulk radial motion of the gas, finding that both star formation and AGN wind feedback contribute to pushing the gas outwards along the minor axis at $\lesssim 1$ Mpc, but AGN jet feedback further causes bulk outflow along the minor axis out to several Mpc, which drives quenching via gas starvation. These results provide observational signatures for the operation of AGN feedback in galaxy quenching.

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 ∼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 ∼1012–1013 M⊙ 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 Ωb/Ωm 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 > 105K).