Title: Origin of Non-axisymmetric Features of Virgo Cluster Early-type Dwarf Galaxies. I. Bar Formation and Recurrent Buckling,
Abstract: A fraction of early-type dwarf galaxies in the Virgo cluster have a disk
component and even possess disk features such as bar, lens, and spiral arms. In
this study, we construct 15 galaxy models that resemble VCC856, considered to
be an infalling progenitor of disk dwarf galaxies, within observational error
ranges, and use $N$-body simulations to study their long-term dynamical
evolution in isolation as well as the formation of bar in them. We find that
dwarf disk galaxies readily form bars unless they have an excessively
concentrated halo or a hot disk. This suggests that infalling dwarf disk
galaxies are intrinsically unstable to bar formation, even without any external
perturbation, accounting for a population of barred dwarf galaxies in the
outskirts of the Virgo cluster. The bars form earlier and stronger in galaxies
with a lower fraction of counter-streaming motions, lower halo concentration,
lower velocity anisotropy, and thinner disk. Similarly to normal disk galaxies,
dwarf disk galaxies also undergo recurrent buckling instabilities. The first
buckling instability tends to shorten the bar and to thicken the disk, and
drives a dynamical transition in the bar pattern speed as well as mass inflow
rate. In nine models, the bars regrow after the mild first buckling instability
due to the efficient transfer of disk angular momentum to the halo, and are
subject to recurrent buckling instabilities to turn into X-shaped bulges.