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We introduce the Simba simulations, the next generation of the Mufasa cosmological galaxy formation simulations run with Gizmo's meshless finite mass hydrodynamics. Simba includes updates to Mufasa's sub-resolution star formation and feedback prescriptions, and introduces black hole growth via the torque-limited accretion model of Angls-Alczar et al. (2017a) from cold gas and Bondi accretion from hot gas, along with black hole feedback via kinetic bipolar outflows and X-ray energy. Ejection velocities are taken to be 10 3 km s -1 at high Eddington ratios, increasing to 8000 km s -1 at Eddington ratios below 2%, with a constant momentum input of 20L/c. Simba further includes an on-the-fly dust production, growth, and destruction model. Our Simba run with (100h -1 Mpc) 3 and 1024 3 gas elements reproduces numerous observables, including galaxy stellar mass functions at z = 0 -6, the stellar mass-star formation rate main sequence, H i and H 2 fractions, the mass-metallicity relation at z 0, 2, star-forming galaxy sizes, hot gas fractions in massive halos, and z = 0 galaxy dust properties. However, Simba also yields an insufficiently sharp truncation of the z = 0 mass function, and too-large sizes for low-mass quenched galaxies. We show that Simba's jet feedback is primarily responsible for quenching massive galaxies.
Davé et al. (Tue,) studied this question.