Forming disc galaxies in major mergers: III. The effect of angular
  momentum on the radial density profiles of disc galaxies
  We study the effect of angular momentum on the surface density profiles of
disc galaxies, using high resolution simulations of major mergers whose
remnants have downbending radial density profiles (type II). As described in
the previous papers of this series, in this scenario, most of the disc mass is
acquired after the collision via accretion from a hot gaseous halo. We find
that the inner and outer disc scalelengths, as well as the break radius,
correlate with the total angular momentum of the initial merging system, and
are larger for high angular momentum systems. We follow the angular momentum
redistribution in our simulated galaxies, and find that, like the mass, the
disc angular momentum is acquired via accretion, i.e. to the detriment of the
gaseous halo. Furthermore, high angular momentum systems give more angular
momentum to their discs, which affects directly their radial density profile.
Adding simulations of isolated galaxies to our sample, we find that the
correlations are valid also for disc galaxies evolved in isolation. We show
that the outer part of the disc at the end of the simulation is populated
mainly by inside-out stellar migration, and that in galaxies with higher
angular momentum, stars travel radially further out. This, however, does not
mean that outer disc stars (in type II discs) were mostly born in the inner
disc. Indeed, generally the break radius increases over time, and not taking
this into account leads to overestimating the number of stars born in the inner
disc.
