X-ray Archaeology of Galaxy Groups

Abstract

We have assembled a sample of 60 galaxy groups in order to study the hot intragroup medium and better understand the processes by which it formed. We have analysed ROSAT data for all 60 groups and have obtained XMM data for a small subset. Here we present an initial analysis of the XMM data for NGC 5171, and a comparison with the ROSAT data. This provides some indication of the reliability of the GEMS ROSAT data as well as demonstrating the additional power of XMM.

We find that NGC 5171 consists of two sub-groups with a bright ridge of emission between the centre of the larger component and a bright optical galaxy. Spectral mapping reveals the gas in this ridge to be hot and bright which may be the result of shock heating following a group merger.

A comparison between results from the two instruments reveals the X-ray temperature and large scale morphology are both reliably determined using ROSAT. However, the low spectral resolution leads to a poorly determined metallicity and the low spatial resolution leads to a poor understanding of the point source contamination, and a corresponding inaccuracy in the group luminosity.