We present a maximum-likelihood weak lensing analysis of the mass distribution in optically selected spectroscopic Galaxy Groups ( G ^ { 3 } Cv5 ) in the Galaxy And Mass Assembly ( GAMA ) survey , using background Sloan Digital Sky Survey ( SDSS ) photometric galaxies .
The scaling of halo mass , M _ { h } , with various group observables is investigated .
Our main results are : 1 ) the measured relations of halo mass with group luminosity , virial volume and central galaxy stellar mass , M _ { \star } , agree very well with predictions from mock group catalogues constructed from a GALFORM semi-analytical galaxy formation model implemented in the Millennium \Lambda CDM N-body simulation ; 2 ) the measured relations of halo mass with velocity dispersion and projected half-abundance radius show weak tension with mock predictions , hinting at problems in the mock galaxy dynamics and their small scale distribution ; 3 ) the median M _ { h } |M _ { \star } measured from weak lensing depends more sensitively on the lognormal dispersion in M _ { \star } at fixed M _ { h } than it does on the median M _ { \star } |M _ { h } .
Our measurements suggest an intrinsic dispersion of \sigma _ { \log ( M _ { \star } ) } \sim 0.15 ; 4 ) Comparing our mass estimates with those in the catalogue , we find that the G ^ { 3 } Cv5 mass can give biased results when used to select subsets of the group sample .
Of the various new halo mass estimators that we calibrate using our weak lensing measurements , group luminosity is the best single-proxy estimator of group mass .