A mechanism of bar formation in disk galaxies: synchronization of apsidal precession

ABSTRACT We discuss the mechanism(s) of bar formation in isolated and tidally interacting disc galaxies using results idealized collision-less N-body simulations galaxies. In order to better understand mechanism, we investigate orbital eccentricities (e), epochs apocentre passages (ta), azimuthal angles at ta (φa), precession rates (Ωpre), for individual stars, as well strengths represented by relative m = 2 Fourier amplitude (A2) pattern speeds (Ωbar). The main are follows. A significant fraction stars with initially different φa Ωpre an galaxy can have similar values within several dynamical time-scales. This synchronization Ωpre, which is referred apsidal (‘APS’) this study, caused enhanced strength tangential component gravitational force. weak seed (A2 < 0.1) first formed through APS local regions a disc, then grows due APS. growth phase (0.1 A2 0.4), proceed more efficiently stronger force from so that it enhance further. positive feedback loop key physical mechanism stellar discs. Bar be severely suppressed discs lower mass fractions and/or higher Q parameters much less efficient proceeds rapidly strong tidal perturbation bars compared spontaneous formation.