Friday, 10 October 2008
The PN.S Elliptical Galaxy Survey: the dark matter in NGC 4494
The PN.S Elliptical Galaxy Survey is an ongoing survey to detect and measure the kinematics of planetary nebulae (PNe) in nearby early-type galaxies. Here they present 255 PNe measurements in the elliptical NGC 4494 out to 7 effective radii (Re). They construct mass models, where they include dark matter haloes to explain the observed kinematics at large radii. This plots shows the dark matter fraction they find in this galaxy and other galaxies in their sample, compared to results from numerical simulations. Overall, the dark matter fraction is lower than predicted in simulations, especially at smaller radii. This indicates a mismatch between observations and theory, with intermediate-luminosity galaxies having low concentration haloes.
From Napolitano et al., from http://arxiv.org/abs/0810.1291