The isolated elliptical NGC 4555 observed with

We present analysis of a Chandra observation of the elliptical galaxy NGC 4555. The galaxy lies in a very low density environment, either isolated from all galaxies of similar mass or on the outskirts of a group. Despite this, NGC 4555 has a large ga s ous halo, extending to ∼60 kpc. We find the mean gas temperature to be ∼0.95 keV and the Iron abundance to be ∼0.5Z⊙. We model the surface brightness, temperature and abundance istribution of the halo and use these results to estimate parameters such as the entropy and cooling time of the gas, and the total gravitational mass of the galaxy. In contrast to re cent results showing that moderate luminosity ellipticals contain relatively small quantiti es of dark matter, our results show that NGC 4555 has a massive dark halo and large mass-to-light rati o (56.8 −35.8 M⊙/LB⊙ at 50 kpc, 42.7 −21.2 at 5re, 1σ errors). We discuss this disparity and consider possible me chanisms by which galaxies might reduce their dark matter content.