Galaxy and Mass Assembly (GAMA): The halo mass of galaxy groups from maximum-likelihood weak lensing

<p>We present a maximum-likelihood weak-lensing analysis of the mass distribution in optically selected spectroscopic Galaxy Groups (G³Cv5) in the Galaxy And Mass Assembly (GAMA) survey, using background Sloan Digital Sky Survey (SDSS) photometric galaxies. The scaling of halo mass,<em>M</em>_h, with various group observables is investigated. Our main results are as follows. (1) The measured relations of halo mass with group luminosity, virial volume and central galaxy stellar mass, <em>M</em>_*, agree very well with predictions from mock group catalogues constructed from a GALFORMsemi-analytical galaxy formation model implemented in the Millennium ΛCDM <em>N</em>-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 <em>M</em>_h|<em>M</em>_*measured from weak lensing depends more sensitively on the lognormal dispersion in <em>M</em>_* at fixed <em>M</em>_h than it does on the median <em>M</em>_*|<em>M</em>_h. Our measurements suggest an intrinsic dispersion of σ_{log(<em>M</em>_*)}∼ 0.15. (4) Comparing our mass estimates with those in the catalogue, we find that the <a href="http://mnras.oxfordjournals.org/content/446/2/1356#ref-73">G</a>³Cv5 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.</p>