Dark-Matter Haloes in Elliptical Galaxies: Lost and Found

Preprint
Publisher Website
Google Scholar
  • 9 February 2005
Abstract
According to the paradigm of cosmology, all galaxies are embedded in massive dark-matter haloes. This picture has been challenged by surprisingly low random stellar velocities observed in the outskirts of a few ordinary elliptical galaxies, which were interpreted as evidence for a puzzling dearth of dark matter in these galaxies (Mendez et al. 2001; Romanowsky et al. 2003). We show that the low velocities are in fact fully compatible with the theory of galaxy formation in dark-matter haloes. Using simulations of disc-galaxy mergers involving dark matter, stars and gas, we find that the stellar orbits in the outer regions of the resulting elliptical galaxies are very elongated. This is because the stars now seen away from the galaxy centre either formed near the centre, or were torn by tidal forces there, and put on outgoing trajectories. We show that these elongated orbits, together with the implied steeply falling density profile of the specific observed tracers and sometimes aided by triaxiality, naturally explain the low velocities despite the massive presence of dark matter.

This publication has 0 references indexed in Scilit: