The Role of Stellar Radial Motions in Shaping Galaxy Surface Brightness
  Profiles
  Aims: The physics driving features such as breaks observed in galaxy surface
brightness (SB) profiles remains contentious. Here, we assess the importance of
stellar radial motions in shaping their characteristics. Methods: We use the
simulated Milky Way-mass, cosmological discs, from the Ramses Disc Environment
Study (RaDES) to characterise the radial redistribution of stars in galaxies
displaying type I (pure exponentials), II (downbending), and III (upbending) SB
profiles. We compare radial profiles of the mass fractions and the velocity
dispersions of different sub-populations of stars according to their birth and
current locations. Results: Radial redistribution of stars is important in all
galaxies regardless of their light profiles. Type II breaks seem to be a
consequence of the combined effects of outward-moving and accreted stars. The
former produces shallower inner profiles (lack of stars in the inner disc) and
accumulate material around the break radius and beyond, strengthening the
break; the latter can weaken or even convert the break into a pure exponential.
Further accretion from satellites can concentrate material in the outermost
parts, leading to type III breaks that can coexist with type II breaks, but
situated further out. Type III galaxies would be the result of an important
radial redistribution of material throughout the entire disc, as well as a
concentration of accreted material in the outskirts. In addition, type III
galaxies display the most efficient radial redistribution and the largest
number of accreted stars, followed by type I and II systems, suggesting that
type I galaxies may be an intermediate case between types II and III. In
general, the velocity dispersion profiles of all galaxies tend to flatten or
even ncrease around the locations where the breaks are found. The age and
metallicity profiles are also affected, exhibiting...[abridged]
