We present the first spectroscopic survey of intrinsically low X-ray luminosity clusters at z \gg 0 , with Hubble Space Telescope ( HST ) WFPC2 imaging and spectroscopy from Calar Alto and WHT-LDSS2 .
We study 172 confirmed cluster members in a sample of ten clusters at 0.23 < z < 0.3 , with L _ { X } \mathrel { \raise 1.505 pt \hbox { $ \scriptstyle < $ } \kern - 6.0 pt \lower 1.72 pt% \hbox { { $ \scriptstyle \sim$ } } } 4 \times 10 ^ { 43 } h ^ { -2 } ergs s ^ { -1 } [ 0.1-2.4 keV ] ( \Omega _ { m } = 0.3 , \Lambda = 0.7 ) .
The core of each cluster is imaged with WFPC2 in the F702W filter , and the spectroscopic sample is statistically complete to M _ { r } \sim - 19.0 + 5 \log { h } , within an 11′ ( \sim 1.8 h ^ { -1 } Mpc ) field .
The clusters are dynamically well-separated from the surrounding field and most have velocity distributions consistent with Gaussians .
The velocity dispersions range from \sim 350 – 850 km s ^ { -1 } , consistent with the local L _ { X } - \sigma correlation .
All ten clusters host a bright , giant elliptical galaxy without emission lines , near the centre of the X-ray emission .
We measure the equivalent width of two nebular emission lines , [ O ii ] and H \alpha , and the H \delta absorption line to spectrally classify the cluster members .
Galaxy morphologies are measured from the HST images , using the two-dimensional surface-brightness fitting software gim2d .
Emission line galaxies in these clusters are relatively rare , comprising only 22 \pm 4 % of the sample .
There is no evidence that these emission-line galaxies are dynamically distinct from the majority of the cluster population , though our sample is too small to rule out the \sim 30 % difference that has been observed in more massive clusters .
We find eleven galaxies , comprising 6 % of the cluster members , which are disk-dominated but show no sign of emission in their spectrum .
Most of these are relatively isolated , spiral galaxies with smooth disks .
We find no cluster members with a starburst or post-starburst spectrum .
The striking similarity between the spectral and morphological properties of galaxies in these clusters and those of galaxies in more massive systems at similar redshifts implies that the physical processes responsible for truncating star formation in galaxies are not restricted to the rare , rich cluster environment , but are viable in much more common environments .
In particular , we conclude that ram pressure stripping or cluster-induced starbursts can not be solely responsible for the low star formation rates in these systems .