Near IR Observations and Dynamics of Barred Galaxies

Abstract

We discuss some of the analytical barred potentials used e.g. for studies of gas flow or orbital structure in barred spirals, and mention their relative merits. Potentials obtained directly from observation are more realistic, but their calculation relies on two major assumptions, i.e. the mass-to-light ratio is constant over the face of a galaxy, and the disc and bar have a constant vertical thickness. Changing the vertical density profile does not seem to influence much the results, provided the same value for the projected light and for < z 2 > are kept. Changing the scale-height, on the other hand, changes the amplitude of the Fourier components of the potential.The most interesting result, however, comes from comparing potentials obtained from images at different wavelength bands. If near-IR rather than B band photometry is used, considerably more dark matter is needed to account for the observed rotation curves.Using the potential calculated from a near-IR image of NGC 4314, we discuss both symmetric and asymmetric periodic orbits in the bar region of that galaxy, and in particular the various 3/1 and 4/1 families.The shape of bars, at least in early type strongly barred galaxies, is quite rectangular-like, in particular near the outer parts of the bar. This could trigger a substantial amount of ergodicity. We discuss the various types of orbits that can account for this shape, presenting the relative merits of each solution.Finally, some suggestions are made for future work with near-IR photometry of barred and, more generally, disc galaxies.