1702.06148
FIRE-2 Simulations: physics versus Numerics in Galaxy formation
Hopkins, Wetzel, et al
FIRE (Feedback in Realistic Environments) project expires the role of feedback in cosmo sims of galaxy formation. Previous FIRE simulations used an identical source code (FIRE-1) for consistency. Now, motivated by the development of more accurate numerics (hydrodynamic solvers, gravitational softening, supernova coupling) and the exploration of new physics (e.g. magnetic fields), introduce FIRE-2, an updated numerical implementation of FIRE physics for the GIZMO code. Run a suite of sims and show FIRE-2 improvements do not qualitative change galaxy-scale properties relative to FIRE-1. Then pursue an extensive study of numerics vs. physics in galaxy sims. Details of the SF algorithm, cooling physics, and chemistry have weak effects, provided that metal-line cooling is included and SF occurs at higher-than-mean densities. Present several new resolution criteria for high-resolution galaxy sims. Most galaxy-scale properties are remarkably robust to the numerics that is tested, proved that: (1) Toomre masses (cold disk scale heights) are resolved, (2) feedback coupling ensures conservation and isotropy, and (3) individual supernovae are time-resolved. As resolution increases, stellar masses and profiles converge first, followed by metal abundances and visual morphologies, then properties of winds and the circumgalactic medium. The central (~kpc) mass concentration of massive (L*) galaxies is sensitive to numerics, particularly how winds ejected into hot haloes are trapped, mixed, and recycled into the galaxy. Multiple feedback mechanisms are required to reproduce observations: SNe regulate stellar masses; OB/AGB mass loss fuels late-time SF; radiative feedback suppresses instantaneous SFRs and accretion onto dwarfs. Provide tables, initial conditions, and the numerical algorithms required to reproduce the simulations.
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