Calibrating an updated SPH scheme within GCD+
  We adapt a modern scheme of smoothed particle hydrodynamics (SPH) to our tree
N-body/SPH galactic chemodynamics code GCD+. The applied scheme includes imple-
mentations of the artificial viscosity switch and artificial thermal
conductivity pro- posed by Morris & Monaghan (1997), Rosswog & Price (2007) and
Price (2008), to model discontinuities and Kelvin-Helmholtz instabilities more
accurately. We first present hydrodynamics test simulations and contrast the
results to runs undertaken without artificial viscosity switch or thermal
conduction. In addition, we also explore the different levels of smoothing by
adopting larger or smaller smoothing lengths, i.e. a larger or smaller number
of neighbour particles, Nnb. We demonstrate that the new version of GCD+ is
capable of modelling Kelvin-Helmholtz instabilities to a simi- lar level as the
mesh code, Athena. From the Gresho vortex, point-like explosion and
self-similar collapse tests, we conclude that setting the smoothing length to
keep the number of neighbour particles as high as Nnb~58 is preferable to
adopting smaller smoothing lengths. We present our optimised parameter sets
from the hydrodynamics tests.
