Consequences of mechanical and radiative feedback from black holes in disc galaxy mergers

We study the effect of active galactic nucleus (AGN) mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disc galaxies. The merging galaxies have mass ratios of 1:1 to 6:1 and include pre-existing hot gaseous haloes to properly account for the global impact of AGN feedback. Using smoothed particle hydrodynamics simulation code (GADGET-3) we compare three models with different AGN feedback models: (1) no black hole and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars and heating associated with the central AGN X-ray radiation. Compared to thermal AGN feedback, the mechanical AGN feedback produces lower thermal X-ray luminosity, higher velocity galactic outflows, and a much greater AGN variability in better agreement with observations. All merger remnants with mechanical AGN feedback with v_w ∼ 10 000 km s^-1 and εf = 2 × 10^-3, independent of their progenitor mass ratios, reproduce the observed relations between stellar velocity dispersion and black hole mass (M_BH-σ) as well as X-ray luminosity (L_X-σ), whereas thermal feedback leads to thermal X-ray luminosity in excess of observations.