  Energetic feedback from supernovae (SNe) and from active galactic nuclei
(AGN) are both important processes that are thought to control how much gas is
able to condense into galaxies and form stars. We show that although both AGN
and SNe suppress star formation, they mutually weaken one another's effect by
up to an order of magnitude in haloes in the mass range for which both feedback
processes are efficient (10^11.25 M_sun < m_200 < 10^12.5 M_sun). These results
demonstrate the importance of the simultaneous, non-independent inclusion of
these two processes in models of galaxy formation to estimate the total
feedback strength. These results are of particular relevance to semi-analytic
models, which implicitly assume the effects of the two feedback processes to be
independent, and also to hydrodynamical simulations that model only one of the
feedback processes.
