The BAHAMAS project: Calibrated hydrodynamical simulations for
  large-scale structure cosmology
  The evolution of the large-scale distribution of matter is sensitive to a
variety of fundamental parameters that characterise the dark matter, dark
energy, and other aspects of our cosmological framework. Since the majority of
the mass density is in the form of dark matter that cannot be directly
observed, to do cosmology with large-scale structure one must use observable
(baryonic) quantities that trace the underlying matter distribution in a
(hopefully) predictable way. However, recent numerical studies have
demonstrated that the mapping between observable and total mass, as well as the
total mass itself, are sensitive to unresolved feedback processes associated
with galaxy formation, motivating explicit calibration of the feedback
efficiencies. Here we construct a new suite of large-volume cosmological
hydrodynamical simulations (called BAHAMAS, for BAryons and HAloes of MAssive
Systems) where subgrid models of stellar and Active Galactic Nucleus (AGN)
feedback have been calibrated to reproduce the present-day galaxy stellar mass
function and the hot gas mass fractions of groups and clusters in order to
ensure the effects of feedback on the overall matter distribution are broadly
correct. We show that the calibrated simulations reproduce an unprecedentedly
wide range of properties of massive systems, including the various observed
mappings between galaxies, hot gas, total mass, and black holes, and represent
a significant advance in our ability to mitigate the primary systematic
uncertainty in most present large-scale structure tests.
