We present spectroscopic confirmation of nine moderate redshift galaxy groups and poor clusters selected from the ROSAT Deep Cluster Survey .
The groups span the redshift range z \sim 0.23 –0.59 and have between 4 and 20 confirmed members .
The velocity dispersions of these groups range from \sim 125 to 650 km s ^ { -1 } .
Similar to X-ray groups at low redshift , these systems contain a significant number of early-type galaxies .
Therefore , the trend for X-ray luminous groups to have high early-type fractions is already in place by at least z \sim 0.5 .
In four of the nine groups , the X-ray emission is clearly peaked on the most luminous early-type galaxy in the group .
However , in several cases the central galaxy is composed of multiple luminous nuclei , suggesting that the brightest group galaxy may still be undergoing major mergers .
In at least three ( and possibly five ) of the groups in our sample , a dominant early-type galaxy is not found at the center of the group potential .
This suggests that many of our groups are not dynamically evolved despite their high X-ray luminosities .
While similar systems have been identified at low redshift , the X-ray luminosities of the intermediate redshift examples are one to three orders of magnitude higher than those of their low redshift counterparts .
We suggest that this may be evidence for group downsizing : while massive groups are still in the process of collapsing and virializing at intermediate redshifts , only low-mass groups are in the process of forming at the present day .