Simba: Cosmological Simulations with Black Hole Growth and Feedback
  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 Angl\'es-Alc\'azar et al. (2017) 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 at high Eddington ratios, increasing to ~8000 km/s 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 (100 Mpc/h)^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, HI and H2 fractions, the
mass-metallicity relation at z=0 and z=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.
