Previous observations of the environments of the lensing galaxies in gravitational lens systems suggest that many of the lensing galaxies are associated with small groups of galaxies .
As a result , we have begun a coordinated program to study the local environments of all known gravitational lens systems .
In this paper , we present results on the gravitational lens system CLASS B0712+472 , which has previously measured source and lens redshifts of ( z _ { \ell } ,z _ { s } ) = ( 0.4060 , 1.339 ) .
Although we have not found a galaxy group associated with the primary lensing galaxy , we have found a foreground group which is spatially coincident with the lens system .
Based on multi-object spectroscopy taken at the Keck 10-m telescope , we have confirmed ten group members with a mean redshift of \bar { z } = 0.2909 .
The resulting velocity dispersion and estimated virial mass are 306 ^ { +110 } _ { -58 } km s ^ { -1 } and 3.0 ^ { +2.2 } _ { -1.2 } \times 10 ^ { 13 } ~ { } h ^ { -1 } M _ { \odot } , respectively , for ( \Omega _ { m } , \Omega _ { \Lambda } ) = ( 0.2 , 0.0 ) .
The dynamical properties of this moderate-redshift group are completely consistent with the range of values found in nearby groups of galaxies .
Five of the group members are red , elliptical-like galaxies , while the remaining five are active , star-forming galaxies .
Based on the spectroscopic results and the publically-available Hubble Space Telescope imaging of nine group members , we find that the early-type fraction is 40 % .
We estimate that the effect of this foreground group on the gravitational lensing potential of B0712+472 is small , producing an external shear which is only a few percent , although the shear could be larger if the group centroid is significantly closer to the lens system than it appears to be .