Active galactic nuclei-driven outflows without immediate quenching in simulations of high-redshift disc galaxies

Abstract

We study outflows driven by active galactic nuclei (AGNs) using high-resolution simulations of idealized z ∼ 2 isolated disc galaxies. Episodic accretion events lead to outflows with velocities >1000 km s-1 and mass outflow rates of about the star formation rate (several tens of M⊙ yr-1). Outflowing winds escape perpendicular to the disc with wide opening angles, and are typically asymmetric (i.e. unipolar) because dense gas above or below the AGN in the resolved disc inhibits outflow. Owing to rapid variability in the accretion rates, outflowing gas may be detectable even when the AGN is effectively 'off'. The highest velocity outflows are sometimes, but not always, concentrated within 2-3 kpc of the galactic centre during the peak accretion. With our purely thermal AGN feedback model-standard in previous literature-the outflowing material is mostly hot (>106 K) and diffuse (nH ≤ 10-2 cm-3), but includes a cold component entrained in the hot wind. Despite the powerful bursts and high outflow rates, AGN feedback has little effect on the dense gas in the galaxy disc. Thus AGN-driven outflows in our simulations do not cause rapid quenching of star formation, although they may remove significant amounts of gas over long (>Gyr) time-scales. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.