  The accretion of the intergalactic medium onto the gaseous disc is used to
explain the generation of galactic warps. A cup-shaped distortion is expected,
due to the transmission of the linear momentum; but, this effect is small for
most incident inflow angles and the predominant effect turns out to be the
transmission of angular momentum, i.e. a torque giving an integral-sign shaped
warp. The torque produced by a flow of velocity ~100 km/s and baryon density
~10^{-25} kg/m^3, which is within the possible values for the intergalactic
medium, is enough to generate the observed warps and this mechanism offers
quite a plausible explanation. The inferred rate of infall of matter, ~1
M_sun/yr, to the Galactic disc that this theory predicts agrees with the
quantitative predictions of chemical evolution resolving key issues, notably
the G-dwarf problem.
  Sanchez-Salcedo (2006) suggests that this mechanism is not plausible because
it would produce a dependence of the scaleheight of the disc with the
Galactocentric azimuth in the outer disc, but rather than being an objection
this is another argument in favour of the mechanism because this dependence is
actually observed in our Galaxy.
