MINOR AXIS ROTATION AND THE INTRINSIC SHAPE OF THE SHELL ELLIPTIC NGC-3923

We present kinematic observations of NGC 3923, one of the best-known e xamples of an elliptical galaxy with shells. Although NGC 3923 has no rotation on its major axis, it has minor axis rotation with an amplitu de of some 20 km s(-1) out to 25 arcsec radius. This is possibily the result of a kinematically decoupled core, but we present arguments aga inst this hypothesis, and if the core were formed by a merger, this mu st have been a different merger from that which gave rise to the shell s. The minor axis rotation suggests that NGC 3923 is prolate or triaxi al, at least in the inner region. A prolate geometry for the whole gal axy would favour the merger model over the interaction model for the s hell formation mechanism. There is other evidence, however, that the s hape of the underlying galaxy changes with radius, in which case it is possible that the minor axis rotation could be confined to the galaxy core. The kinematics could reflect a triaxial mass distribution, in w hich the long and short axes are aligned with the photometric major an d minor axes, and the axial ratios change such that the galaxy is near -prolate in the inner regions and near-oblate at larger radii. Measuri ng the rotation curve to about double this radius along the minor axis , as well as offset from the nucleus along the major axis at the radiu s of the innermost shells, would enable the true extent of the minor a xis rotation to be determined.