  The Milky Way as well as a majority of external galaxies possess a thick
disc. However, the dynamical role of the (geometrically) thick disc on the bar
formation and evolution is not fully understood. Here, we investigate the
effect of thick discs in bar formation and evolution by means of a suite of
N-body models of (kinematically cold) thin-(kinematically hot) thick discs. We
systematically vary the mass fraction of the thick disc, the thin-to-thick disc
scale length ratio as well as thick disc's scale height to examine the bar
formation under diverse dynamical scenarios. Bars form almost always in our
models, even in presence of a massive thick disc. The part of the bar
constituted by the thick disc closely follows the overall growth and temporal
evolution of the part of the bar constituted by the thin disc, only the part of
the bar in the thick disc is weaker than the part of the bar in the thin disc.
The formation of stronger bars is associated with a simultaneous larger loss of
angular momentum and a larger radial heating. In addition, we demonstrate a
preferential loss of angular momentum and a preferential radial heating of disc
stars, along the azimuthal direction within the extent of the bar, in both thin
and thick disc stars. For purely thick disc models (without any thin disc), the
bar formation critically depends on the disc scale length and scale height. A
larger scale length and/or a larger vertical scale height delays the bar
formation time and/or suppresses the bar formation almost completely in
thick-disc-only models. We find that the Ostriker-Peeble criterion predicts the
bar instability scenarios in our models better than the
Efstathiou-Lake-Negroponte criterion.
