ABSTRACT

Near–IR photometry within the nuclei of 3 barred spiral galaxies reveals 63–100° isophote twists between the innermost regions and the PA's of the major bars. New N–body simulations indicate that such twists can be best described as the response of the stars to the influence on the potential of the gas within circumnuclear rings.

INTRODUCTION AND OBSERVATIONS

The clearest consequence of barred potentials is manifest in those galaxies undergoing enhanced nuclear star formation, particularly those possessing circumnuclear rings (CNRs). These rings probably form in the region of the inner Lindblad resonances (ILRs), the accumulation of molecular gas acting to enhance star formation. Isophote twists have been noted previously in the centres of barred potentials, both in the stars (Jarvis et al. 1988) and the gas (Devereux et al. 1992), and a link has been suggested between these twists and CNR's.

We have obtained near–IR (1.2–2.2 μm) photometry within the central regions of the barred spirals NGC 1097, NGC 4736 and NGC 5728. Twists of 63°–100° are observed between the innermost isophotes and the known position angles of the bar/lens components, corresponding to the most unambiguous and extreme such detections in any barred spiral later than S0/a. In NGC 1097 and NGC 5728 such twists are immediately interior to the radii of known CNRs. We have considered three possibilities by which such twists could arise.

In weak–intermediate strength bars, there exist two ILRs. The (stable) x2 orbital family dominate between the ILRs and are orthogonal to the main bar.