Light profiles and pattern speeds for bars in early- and late-type galaxies

Abstract

J, H, and K infrared band observations of 11 barred galaxies, and B and I band observations of 8 barred galaxies, spanning a wide range of Hubble types, confirm the trend found earlier that early types tend to have flat light profiles along the bars and late types have exponential light profiles. Both types have nearly continuous exponential light profiles when azimuthally averaged. The flat profiles arise from excess old and young stars at the bar ends, presumably where the orbits crowd together near the inner 4:1 resonance. The exponential profiles have no such crowding and also lack offset leading dustlanes as if there is no inner Lindblad resonance inside the bar. Arm/interarm contrasts in J band increase with radius near the center and then become constant or decrease with radius at a value of arm/interarm∼6. This saturation of wave amplitude tends to occur at the same radius where the arms bifurcate or become multiple, suggesting that spiral waves limit their own amplitudes at large radii by coupling to higher order modes. A compilation of bar pattern speeds from the literature, mostly covering early types, generally puts corotation at a distance between 1.2 and 1.4 times the bar semi-major axis length, usually in the middle of the strong part of the spiral arms. These observations imply that early-type bars end because of orbit resonance scattering slightly beyond their inner 4:1 resonances; the spirals and rings in these galaxies appear to corotate with the bars. Patterns speeds in late type bars remain unknown. © 1996 American Astronomical Society.