The collaborative effect of ram pressure and merging on star formation
  and stripping fraction
  Aims: We investigate the effect of ram pressure stripping (RPS) on
simulations of merging pairs of gas-rich spiral galaxies. Our goal is to
provide an estimate of the combined effect of merging and RPS on stripping
efficiency and star formation rate.
  Methods: We make use of the combined N-body/hydrodynamic code GADGET-2. In
our simulations, we vary mass ratios between 1:4 and 1:8 in a binary merger. We
sample different geometric configurations of the merging systems (edge-on and
face-on mergers, different impact parameters). Furthermore, we vary the
properties of the intracluster medium (ICM) in rough steps: The speed of the
merging system relative to the ICM between 500 and 1000 km/s, the ICM density
between $10^{-29}$ and $10^{-27}$ g/cm$^3$, and the ICM direction relative to
the mergers' orbital plane. Ram pressure is kept constant within a simulation
time period, as is the ICM temperature of $10^7$ K. Each simulation in the ICM
is compared to simulations of the merger in vacuum and the non-merging galaxies
with acting ram pressure.
  Results: Averaged over the simulation time (1 Gyr) the merging pairs show a
negligible 5% enhancement in SFR, when compared to single galaxies under the
same environmental conditions. The SFRs peak at the time of the galaxies first
fly-through. There, our simulations show SFRs of up to 20 M$_{\odot}$/yr
(compared to 3 M$_{\odot}$/yr of the non-merging galaxies in vacuum). In the
most extreme case, this constitutes a short-term ($<50$ Myr) SFR increase of
50% over the non-merging galaxies experiencing ram pressure. The wake of
merging galaxies in the ICM typically has a third to half the star mass seen in
the non-merging galaxies and 5% to 10 % less gas mass. The joint effect of RPS
and merging, according to our simulations, is not significantly different from
pure ram pressure effects.
