How to bend galaxy disc profiles II: stars surfing the bar in Type-III
  discs
  The radial profiles of stars in disc galaxies are observed to be either
purely exponential (Type-I), truncated (Type-II) or anti-truncated (Type-III)
exponentials. Controlled formation simulations of isolated galaxies can
reproduce all of these profile types by varying a single parameter, the initial
halo spin. In this paper we examine these simulations in more detail in an
effort to identify the physical mechanism that leads to the formation of
Type-III profiles. The stars in the anti-truncated outskirts of such discs are
now on eccentric orbits, but were born on near-circular orbits at much smaller
radii. We show that, and explain how, they were driven to the outskirts via
non-linear interactions with a strong and long-lived central bar, which greatly
boosted their semi-major axis but also their eccentricity. While bars have been
known to cause radial heating and outward migration to stellar orbits, we link
this effect to the formation of Type-III profiles. This predicts that the
anti-truncated parts of galaxies have unusual kinematics for disc-like stellar
configurations: high radial velocity dispersions and slow net rotation. Whether
such discs exist in nature, can be tested by future observations.
