The dark balance: quantifying the inner halo response to active galactic nuclei feedback in galaxies

This paper presents a study of the impact of supermassive black hole (SMBH) feedback on dark matter (DM) haloes in numerical NIHAO (Numerical Investigation of a Hundred Astrophysical Object) simulations of galaxies. In particular, the amount of DM displaced via active galactic nuclei (AGNs) feedback and the physical scale over which AGN feedback affects the DM halo are quantified by comparing NIHAO simulations with and without AGN feedback. NIHAO galaxies with log (M*/M-circle star) >= 10.0 show a growing central DM suppression of 0.2 dex (similar to 40 per cent) from z = 1.5 to the present relative to no AGN feedback simulations. The growth of the DM suppression is related to the mass evolution of the SMBH and the gas mass in the central regions. For the most massive NIHAO galaxies with log (M*/M-circle star) > 10.5, partially affected by numerical resolution, the central DM suppression peaks at z = 0.5 after which halo contraction overpowers AGN feedback due a shortage of gas and thus, SMBH growth. The spatial scale, or 'sphere of influence', over which AGN feedback affects the DM distribution decreases as a function of time for Milky Way-mass galaxies (from similar to 16 kpc at z = 1.5 to similar to 7.8 kpc at z = 0) as a result of halo contraction due to stellar growth. For the most massive NIHAO galaxies, the size of the sphere of influence remains constant (similar to 16 kpc) for z > 0.5 owing to the balance between AGN feedback and halo contraction.