14.2. Bar-Ring Misalignment
Most inner and outer rings in barred galaxies are aligned with the bar (section 9.3). Exceptions do exist, however, like in ESO 565-11 (Buta et al. 1995a; see Figure 82) and others described by Buta (1995), but they are rare. Therefore, there is no incompatibility with the theoretical predictions that they should be transient features. Possible scenarios include a tidal interaction with a companion (see, for example, Noguchi 1987), since these galaxies are sometimes members of loose groups, or the relaxation of the disk through mass concentration driven by the bar. Indeed, as soon as a relatively high fraction of the gas has accumulated in the center, the potential and rotation curve are significantly modified, and so is the bar structure; a secondary bar can even decouple from the primary one, as developed in section 16, and misaligned components are expected at the transition phase. A secondary bar can have a different pattern speed from the primary one, so that no alignment is expected between the two bars. For the peculiar case of ESO 565-11, the bar is rather weak and of the ``ansae'' type, which indicates possibly a half-destroyed bar (cf. section 15). The nuclear ring is the site of a conspicuous starburst, so that the hypothesis of a recent gas concentration, and consequent relaxation of the potential is the most plausible. The galaxy is not yet highly concentrated, so that the decoupling of a secondary bar is unlikely.
As for the alignment of the nuclear bars, they are much more difficult to ascertain, and highly elongated nuclear rings are rare (see section 9.3). When elongated, they are in general misaligned with the main bar, as in ESO 565-11. Due to the presence of two inner Lindblad resonances in highly concentrated galaxies, some phase-shift between the bar and the nuclear ring is expected (e.g., Shaw et al. 1993). Also, a secondary wave with a different pattern speed may exist, which implies misalignment.