The first major science programme for the PN.S will be to study the kinematics in a large sample of bright, round elliptical galaxies. With a high abundance of observable PNe per galaxy, and with presumably simpler dynamics than in more flattened ellipticals, these systems should be the most immediately fruitful for dynamical analysis. On the basis of previous experience and calculations (see below), we expect to obtain 100-400 PN velocities per galaxy, extending to 5-15 Reff (see figure below); these data will be combined with available stellar absorption line kinematical data from the inner parts. With ~ 100 velocities, we will be able to measure the rotational structure of a galaxy, and make a rough estimate of the total halo mass. With ~ 250 velocities, using our existing orbit-modelling methods (Romanowsky & Kochanek 2000), we can measure the total mass of the galaxy to ~ 20% and quantify the anisotropy of the orbits (the parameter) to ~ 30%, both representing unprecedented degrees of accuracy.

A sample of 433 planetary nebulae (PNe) overlaid on the stellar isophotes of NGC 5128, where Reff 5 kpc. The PNe marked with circles have negative relative velocities, and the PNe with crosses have positive velocities. marks the position of the rotation axis. With our proposed observations, we will be able to obtain data of comparable quality for a much more representative sample of elliptical galaxies. From Hui et al. (1995). (Click on figure to enlarge.)

  • References

    last modified by AJR, 14 January 2002