Spinning dark matter halos promote bar formation
  Stellar bars are the most common non-axisymmetric structures in galaxies and
their impact on the evolution of disc galaxies at all cosmological times can be
significant. Classical theory predicts that stellar discs are stabilized
against bar formation if embedded in massive spheroidal dark matter halos.
However, dark matter halos have been shown to facilitate the growth of bars
through resonant gravitational interaction. Still, it remains unclear why some
galaxies are barred and some are not. In this study, we demonstrate that
co-rotating (i.e., in the same sense as the disc rotating) dark matter halos
with spin parameters in the range of $0 \le \lambda_{\mathrm{dm}} \le 0.07$ -
which are a definite prediction of modern cosmological models - promote the
formation of bars and boxy bulges and therefore can play an important role in
the formation of pseudobulges in a kinematically hot dark matter dominated disc
galaxies. We find continuous trends for models with higher halo spins: bars
form more rapidly, the forming slow bars are stronger, and the final bars are
longer. After 2 Gyrs of evolution, the amplitude of the bar mode in a model
with $\lambda_{\mathrm{dm}} = 0.05$ is a factor of ~6 times higher, A_2/A_0 =
0.23, than in the non-rotating halo model. After 5 Gyrs, the bar is ~ 2.5 times
longer. The origin of this trend is that more rapidly spinning (co-rotating)
halos provide a larger fraction of trailing dark matter particles that lag
behind the disc bar and help growing the bar by taking away its angular
momentum by resonant interactions. A counter-rotating halo suppresses the
formation of a bar in our models. We discuss potential consequences for forming
galaxies at high-redshift and present day low mass galaxies which have
converted only a small fraction of their baryons into stars.
