Thin discs, thick dwarfs and the effects of stellar feedback
  We investigate the role of stellar mass in shaping the intrinsic thickness of
galaxy discs by determining the probability distribution of apparent axis
ratios (b/a) for two different samples that probe the faint end of the galaxy
luminosity function. We find that the b/a distribution has a characteristic
'U-shape' and identify a limiting mass M_* ~ 2x10^9 M_sun below which low-mass
galaxies start to be systematically thicker. This tendency holds for very faint
(M_B ~ -8) dwarfs in the Local Volume, which are essentially spheroidal
systems. We argue that galaxy shape is the result of the complex interplay
between mass, specific angular momentum and stellar feedback effects. Thus, the
increasing importance of turbulent motions in lower mass galaxies leads to the
formation of thicker systems, a result supported by the latest hydrodynamical
simulations of dwarf galaxy formation and other theoretical expectations. We
discuss several implications of this finding, including the formation of bars
in faint galaxies, the deprojection of HI line profiles and simulations of
environmental effects on the dwarf galaxy population.
