Star formation in mergers with cosmologically motivated initial
  conditions
  We use semi-analytic models and cosmological merger trees to provide the
initial conditions for multi-merger numerical hydrodynamic simulations, and
exploit these simulations to explore the effect of galaxy interaction and
merging on star formation (SF). We compute numerical realisations of twelve
merger trees from z=1.5 to z=0. We include the effects of the large hot gaseous
halo around all galaxies, following recent obervations and predictions of
galaxy formation models. We find that including the hot gaseous halo has a
number of important effects. Firstly, as expected, the star formation rate on
long timescales is increased due to cooling of the hot halo and refuelling of
the cold gas reservoir. Secondly, we find that interactions do not always
increase the SF in the long term. This is partially due to the orbiting
galaxies transferring gravitational energy to the hot gaseous haloes and
raising their temperature. Finally we find that the relative size of the
starburst, when including the hot halo, is much smaller than previous studies
showed. Our simulations also show that the order and timing of interactions are
important for the evolution of a galaxy. When multiple galaxies interact at the
same time, the SF enhancement is less than when galaxies interact in series.
All these effects show the importance of including hot gas and cosmologically
motivated merger trees in galaxy evolution models.
