Diffuse X-ray Emission From the NGC 2300 Group of Galaxies: Implications for Dark Matter and Galaxy Formation in Small Groups
Abstract
We report the detection of a hot, diffuse inter-group medium (IGM) with the ROSAT PSPC in the NGC 2300 group of galaxies. This is the first time such a gas component has been found in a \lq`typical\rq\rq \ group, which has only three major members. The gas distribution is roughly symmetric, centered ~ 3' from the elliptical NGC 2300 and extends to a radius of at least 0.2 h50() -1 Mpc. A Raymond-Smith (1977) hot plasma model provides an excellent fit to the x-ray spectrum, with a best fit value to the temperature of 0.9{() +0.15_-0.14} keV and abundance of 0.06{() +0.12_-0.05} solar. The temperature and luminosity of the diffuse gas follow the correlations between these two parameters found for clusters, suggesting both the gas and the galaxies respond to the same potential. A reasonable estimate of the baryonic mass in galaxies and diffuse gas indicates that baryons can account for ~ 4% of the mass required for gravitational containment of the hot diffuse gas. A conspiracy of errors could push this number no higher than 15%. This is one of the strongest pieces of evidence that dark matter dominates small groups such as this one, and is in agreement with dynamical arguments for masses of groups of galaxies. The IGM in this group has the lowest metal abundance yet found in diffuse gas in a group or cluster. While not as dense a gas as in clusters, the IGM still appears capable of significantly affecting the outer parts of the group galaxies. In particular, the spiral NGC 2276 displays asymmetries in its optical and radio morphologies suggestive of an ongoing IGM-galaxy encounter.
- Publication:
-
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1992
- Bibcode:
- 1992AAS...181.1514M