2019MNRAS.486..523B

We investigate the connection between the vertical structure of stellar discs and the formation of bars using high-resolution simulations of galaxies in isolation and in the cosmological context. In particular, we simulate a suite of isolated galaxy models that have the same Toomre Q parameter and swing amplification parameter but that differ in the vertical scale height and velocity dispersion. We find that the onset of bar formation occurs more slowly in models with thicker discs. Moreover, thicker discs and discs in simulations with larger force softening are found to be more resilient to buckling, which acts to regulate the length and strength of bars. We simulate disc-halo systems in the cosmological environment using a disc-insertion technique developed in a previous paper. In this case, bar formation is driven by the stochastic effects of a triaxial halo and subhalo-disc interactions and the initial growth of bars appears to be relatively insensitive to the thickness of the disc. On the other hand, thin discs in cosmological haloes do appear to be more susceptible to buckling than thick ones and therefore bar strength correlates with disc thickness as in the isolated case. Thus, one can form discs in cosmological simulations with relatively weak bars or no bars at all provided the discs as thin as the discs we observe and the softening length is smaller than the disc scale height.