We present X–ray and optical spectroscopic observations of twelve galaxy groups and clusters identified within the XMM Large–Scale Structure ( LSS ) survey .
Groups and clusters are selected as extended X–ray sources from a 3.5 deg ^ { 2 } XMM image mosaic above a flux limit 8 \times 10 ^ { -15 } erg s ^ { -1 } cm ^ { -2 } in the [ 0.5–2 ] keV energy band .
Deep BVRI images and multi–object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29 < z < 0.56 .
We combine line–of–sight velocity dispersions with the X–ray properties of each structure computed from a two–dimensional surface brightness model and a single temperature fit to the XMM spectral data .
The resulting distribution of X–ray luminosity , temperature and velocity dispersion indicate that the XMM–LSS survey is detecting low–mass clusters and galaxy groups to redshifts z < 0.6 .
Confirmed systems display little or no evidence for X–ray luminosity evolution at a given X–ray temperature compared to lower redshift X–ray group and cluster samples .
A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM–LSS survey .