Dear Editorials, Science and an Astronomy friends,

Date: Wed Oct 27, 2004 8:22 am
Subject: The isolated elliptical NGC 4555 observed with Chandra
http://arxiv.org/abs/astro-ph/0407552

Authors:((1) Harvard-Smithsonian Center for Astrophysics (2) University of
Birmingham, UK)
Comments: 10 pages, 7 postscript figures, accepted for publication in
MNRAS

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 gaseous halo, extending to ~60 kpc. We find the mean gas
temperature to be ~0.95 keV and the Iron abundance to be ~0.5 solar. We model
the surface brightness, temperature and abundance distribution 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 recent
results showing that moderate luminosity ellipticals contain relatively small
quantities of dark matter, our results show that NGC 4555 has a massive dark
halo and large mass-to-light ratio (56.8 [+34.2,-35.8] solar at 50 kpc, 42.7
[+14.6,-21.2] solar at 5 effective radii, 1 sigma errors). We discuss this
disparity and consider possible mechanisms by which galaxies might reduce their
dark matter content.
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