The dynamics of an elliptical galaxy within a couple of effective radii can be probed effectively by stars. However, at larger distances planetary nebulae (PNe) replace stars as the tracer ofthe dynamics. Making use of the motion of PNe, Romanowsky et al. measured the dynamics of three luminous elliptical galaxies (NGC821, NGC3379 and NGC4494) at large distances from the galactic centre. They found that little dark matter is needed up to six effective radii. Milgrom and Sanders showed that this result can be understood in the framework of MOdified Newtonian Dynamics (MOND). As more data are available in the past decade, we revisit this problem. We combine PNe data (up to six to eight effective radii) and stellar data from SAURON of seven elliptical galaxies, including those three galaxies in Romanowsky et al. with updated data and four other galaxies which have not been analysed before. We conclude that the dynamics of these galaxies can be well explained by MOND.
- Dark matter
- Galaxies: elliptical and lenticular, cD
- Galaxies: kinematics and dynamics
- Gravitational lensing: strong