THE BAR IN NGC-4596

The light from the SBa galaxy is decomposed into three components: an oblate spheroidal bulge with luminosity 4.7 × 109 L⊙ and true ellipticity ∈ = 0.26, a rectangular bar with luminosity 6.7 × 109 L⊙ and size 10.0 × 2.6 kpc, and a constant-intensity lens with luminosity 3.9 × 109 L⊙ out to 8.7 kpc. The bulge radial luminosity profile is best described by a truncated King model approximation plus a Gaussian core rather than a De Vaucouleurs law. The azimuthally averaged bar and lens form an exponential profile with scale length 3.2 kpc. The dynamics are explored in detail. An approximate dynamical model is constructed by taking the bulge to be an oblate isotropic rotator and by scaling the predicted disk kinematics from an n-body simulation of Sparke and Sellwood. Spectroscopic observations taken at three different position angles show that the velocity field deviates less from circular rotation than the simple model would predict and that the pattern speed is close to its maximum possible value. A curious peak is seen in the rotation curve at 0.35 kpc. The characteristic slowing-down time due to transfer of angular momentum to the outer Lindblad resonance is of order 6-20 × 109 yr. In comparison with the SB0 galaxy NGC 936, NGC 4596 is larger, has a lower surface brightness, smaller internal motions, the same mass/light ratio, and the same ratio of corotation radius to bar length.