The EAGLE simulations of galaxy formation: the importance of the
  hydrodynamics scheme
  We present results from a subset of simulations from the "Evolution and
Assembly of GaLaxies and their Environments" (EAGLE) suite in which the
formulation of the hydrodynamics scheme is varied. We compare simulations that
use the same subgrid models without re-calibration of the parameters but
employing the standard GADGET flavour of smoothed particle hydrodynamics (SPH)
instead of the more recent state-of-the-art ANARCHY formulation of SPH that was
used in the fiducial EAGLE runs. We find that the properties of most galaxies,
including their masses and sizes, are not significantly affected by the details
of the hydrodynamics solver. However, the star formation rates of the most
massive objects are affected by the lack of phase mixing due to spurious
surface tension in the simulation using standard SPH. This affects the
efficiency with which AGN activity can quench star formation in these galaxies
and it also leads to differences in the intragroup medium that affect the X-ray
emission from these objects. The differences that can be attributed to the
hydrodynamics solver are, however, likely to be less important at lower
resolution. We also find that the use of a time step limiter is important for
achieving the feedback efficiency required to match observations of the
low-mass end of the galaxy stellar mass function.
