  We identify a large sample of isolated bright galaxies and their fainter
satellites in the 2dF Galaxy Redshift Survey (2dFGRS). We analyse the dynamics
of ensembles of these galaxies selected according to luminosity and
morphological type by stacking the positions of their satellites and estimating
the velocity dispersion of the combined set. We test our methodology using
realistic mock catalogues constructed from cosmological simulations. The method
returns an unbiased estimate of the velocity dispersion provided that the
isolation criterion is strict enough to avoid contamination and that the
scatter in halo mass at fixed primary luminosity is small. Using a maximum
likelihood estimator that accounts for interlopers, we determine the satellite
velocity dispersion within a projected radius of 175 kpc/h. The dispersion
increases with the luminosity of the primary and is larger for elliptical
galaxies than for spiral galaxies of similar bJ luminosity. Calibrating the
mass-velocity dispersion relation using our mock catalogues, we find a
dynamical mass within 175 kpc/h of M_175 ~ 4.0^{+2.3}_{-1.5} 10^12 (L_bJ/L_*)
M_sol/h for elliptical galaxies and M_175 ~ 6.3^{+6.3}_{-3.1} 10^11
(L_bJ/L_*)^1.6 Msol/h for spiral galaxies. Finally, we compare our results with
recent studies and investigate their limitations using our mock catalogues.
