Cosmological Simulations of Quasar Fueling to Subparsec Scales Using Lagrangian Hyper-refinement
We present cosmological hydrodynamic simulations of a quasar-mass halo (M halo ≈ 1012.5 M ⊙ at z = 2) that for the first time resolve gas transport down to the inner 0.1 pc surrounding the central massive black hole. We model a multiphase interstellar medium including stellar feedback by supernovae, stellar winds, and radiation, and a hyper-Lagrangian refinement technique increasing the resolution dynamically approaching the black hole. We do not include black hole feedback. We show that the subpc inflow rate (1) can reach ∼6 M ⊙ yr−1 roughly in steady state during the epoch of peak nuclear gas density (z ∼ 2), sufficient to power a luminous quasar, (2) is highly time variable in the pre-quasar phase, spanning 0.001–10 M ⊙ yr−1 on Myr timescales, and (3) is limited to short (∼2 Myr) active phases (0.01–0.1 M ⊙ yr−1) followed by longer periods of inactivity at lower nuclear gas density and late times (z ∼ 1), owing to the formation of a hot central cavity. Inflowing gas is primarily cool, rotational support dominates over turbulence and thermal pressure, and star formation can consume as much gas as provided by inflows across 1 pc–10 kpc. Gravitational torques from multiscale stellar non-axisymmetries dominate angular momentum transport over gas self-torquing and pressure gradients, with accretion weakly dependent on black hole mass. Subpc inflow rates correlate with nuclear (but decouple from global) star formation and can exceed the Eddington rate by ×10. The black hole can move ∼10 pc from the galaxy center on ∼0.1 Myr. Accreting gas forms pc-scale, rotationally supported, obscuring structures often misaligned with the galaxy-scale disk. These simulations open a new avenue to investigate black hole–galaxy coevolution.