Dynamical triggering of starbursts
  Galaxy interactions/mergers, gravitational instabilities and density waves, such as bars, are frequently invoked to trigger starbursts. These mechanisms have been explored through numerical simulations, with the help of various star formation recipes. Gravitational instabilities are necessary to initiate star formation, but the main trigger might be the gas flows, to provide sufficient fuel in a short time-scale. Gas accretion is also acting on the dynamics, in favoring bars/spirals, which will drive the gas inwards. Large amounts of external gas accretion are required to explain the bar frequency, and this accretion rate can be provided by the cosmic filaments, as supported by cosmological simulations. Subsequent interactions can then trigger starbursts by driving this accreted gas inwards. 
F. Combes (LERMA, Observatoire de Paris)