How Ram Pressure Drives Radial Gas Motions in the Surviving Disk

Galaxy evolution can be dramatically affected by the environment, especially by the dense environment of a galaxy cluster. Recent observational studies show that massive galaxies undergoing strong ram-pressure stripping (RPS) have an enhanced frequency of nuclear activity. We investigate this topic using a suite of wind-tunnel hydrodynamical simulations of a massive M star = 10^11 Msun disk galaxy with 39 pc resolution and including star formation and stellar feedback. We find that RPS increases the inflow of gas to the galaxy center regardless of the wind impact angle. This increase is driven by the mixing of interstellar and nonrotating intracluster media at all wind angles, and by increased torque on the inner disk gas, mainly from local pressure gradients when the intracluster medium (ICM) wind has an edge-on component. In turn, the strong pressure torques are driven by rising ram pressure. We estimate the black hole (BH) accretion using Bondi-Hoyle and torque models, and compare it with the mass flux in the central 140 pc region. We find that the torque model predicts much less accretion onto the BH of a RPS galaxy than the Bondi-Hoyle estimator. We argue that both models are incomplete: the commonly used torque model does not account for torques caused by the gas distribution or local pressure gradients, while the Bondi-Hoyle estimator depends on the sound speed of the hot gas, which includes the ICM in stripped galaxies. An estimator that accounts for this missing physics is required to capture BH accretion in a RPS galaxy.