SPHGal: Smoothed Particle Hydrodynamics with improved accuracy for
  Galaxy simulations
  We present the smoothed-particle hydrodynamics implementation SPHGal, which
combines some recently proposed improvements in GADGET. This includes a
pressure-entropy formulation with a Wendland kernel, a higher order estimate of
velocity gradients, a modified artificial viscosity switch with a modified
strong limiter, and artificial conduction of thermal energy. With a series of
idealized hydrodynamic tests we show that the pressure-entropy formulation is
ideal for resolving fluid mixing at contact discontinuities but performs
conspicuously worse at strong shocks due to the large entropy discontinuities.
Including artificial conduction at shocks greatly improves the results. In
simulations of Milky Way like disk galaxies a feedback-induced instability
develops if too much artificial viscosity is introduced. Our modified
artificial viscosity scheme prevents this instability and shows efficient shock
capturing capability. We also investigate the star formation rate and the
galactic outflow. The star formation rates vary slightly for different SPH
schemes while the mass loading is sensitive to the SPH scheme and significantly
reduced in our favored implementation. We compare the accretion behavior of the
hot halo gas. The formation of cold blobs, an artifact of simple SPH
implementations, can be eliminated efficiently with proper fluid mixing, either
by conduction and/or by using a pressure-entropy formulation.
