Type-II surface brightness profiles in edge-on galaxies produced by
  flares
  Previous numerical studies had apparently ruled out the possibility that
flares in galaxy discs could give rise to the apparent breaks in their
luminosity profiles when observed edge-on. However the studies have not, until
now, analyzed this hypothesis systematically using realistic models for the
disc, the flare, and the bulge. We revisit this theme by analyzing a series of
models which sample a wide range of observationally based structural parameters
for these three components. We have considered realistic distributions of bulge
to disc ratios, morphological parameters of bulges and discs, vertical scale
heights of discs and their radial gradients defining the flare for different
morphological types and stellar mass bins, based on observations. The surface
brightness profiles for the face-on and edge-on views of each model were
simulated to find out whether the flared disc produces a Type-II break in the
disc profile when observed edge-on, and if so under what conditions. Contrary
to previous claims, we find that discs with realistic flares can produce
significant breaks in discs when observed edge-on. Specifically a flare with
the parameters of that of the Milky Way would produce a significant break of
the disc at a Rbreak of ~8.6 kpc if observed edge-on. Central bulges have no
significant effects on the results. These simulations show that flared discs
can explain the existence of many Type-II breaks observed in edge-on galaxies,
in a range of galaxies with low-to-intermediate break strength values of
-0.25<S<-0.1.
