Disc heating: possible link between weak bars and superthin galaxies
  The extreme flatness of stellar discs in superthin galaxies is puzzling and
the apparent dearth of these objects in cosmological simulation poses
challenging problem to the standard cold dark matter paradigm. Irrespective of
mergers or accretion that a galaxy might be going through, stars are heated as
they get older while they interact with the spirals and bars which are
ubiquitous in disc galaxies -- leading to a puffed up stellar disc. It remains
unclear how superthin galaxies maintain their thinness through the cosmic
evolution.
  We follow the internal evolution of a sample of 16 initially extremely thin
stellar discs using collisionless N-body simulation. All of these discs
eventually form a bar in their central region. Depending on the initial
condition, some of these stellar discs readily form strong bars while others
grow weak bars over secular evolution time scale. We show that galaxies with
strong bars heat the stars very efficiently, eventually making their stellar
discs thicker. On the other hand, stars are heated very slowly by weak bars --
as a result, galaxies hosting weak bars are able to maintain their thinness
over several billion years, if left isolated. We suggest that some of the
superthin galaxies might as well be forming weak bars and thereby prevent any
strong vertical heating which in turn helps maintaining their thinness during
the course of secular evolution.
