The surprising anisotropy of fast rotating, discy elliptical galaxies

The projected kinematical properties of unequal-mass merger remnants of disc galaxies are analysed and shown to agree well with observations of discy, fast rotating elliptical galaxies. This supports the major merger hypothesis of early-type galaxy formation. However, in contrast to previous claims, the merger remnants are very anisotropic with values of the anisotropy parameter which are similar to equal-mass merger remnants that form boxy, slowly rotating ellipticals. Including gas in the simulations does not change this result, although the line-of-sight velocity profile and the intrinsic orbital structure are strongly affected by the presence of gas. The kinematical difference between boxy and discy ellipticals appears not to be the amount of anisotropy but rather the rotation and shape of the velocity dispersion tensor. The apparent isotropy of observed discy ellipticals is shown to result from inclination effects. Even small inclination angles strongly reduce the measured anisotropy of fast rotating systems, seen in projection. A second problem is the limited amount of information that is available when measuring only the central velocity dispersion and a characteristic rotation and ellipticity. Methods are investigated that allow a better determination of the intrinsic anisotropy of fast rotating early-type galaxies with known inclination angles.