We present the first results of a multi-object spectroscopic ( MOS ) campaign to follow up cluster candidates located via weak lensing .
Our main goals are to search for spatial concentrations of galaxies that are plausible optical counterparts of the weak lensing signals , and to determine the cluster redshifts from those of member galaxies .
Around each of 36 targeted cluster candidates , we obtain 15 - 32 galaxy redshifts .
For 28 of these targets , we confirm a secure cluster identification , with more than five spectroscopic galaxies within a velocity of \pm 3000 km/s .
This includes three cases where two clusters at different redshifts are projected along the same line-of-sight .
In 6 of the 8 unconfirmed targets , we find multiple small galaxy concentrations at different redshifts , each containing at least three spectroscopic galaxies .
The weak lensing signal around those systems is thus probably created by the projection of groups or small clusters along the same line-of-sight .
In both the remaining two targets , a single small galaxy concentration is found .

We evaluate the weak lensing mass of confirmed clusters via two methods : aperture densitometry and by fitting to an NFW model .
In most cases , these two mass estimates agree well .
In some candidate super-cluster systems , we find additional evidence of filaments connecting the main density peak to additional nearby structure .
For a subsample of our most cleanly measured clusters , we investigate the statistical relation between their weak lensing mass ( M _ { NFW } , \sigma _ { sis } ) and the velocity dispersion of their member galaxies ( \sigma _ { v } ) , comparing our sample with optically and X-ray selected samples from the literature .
Our lensing-selected clusters are consistent with \sigma _ { v } = \sigma _ { sis } , with a similar scatter to the optically and X-ray selected clusters .
We thus find no evidence of selection bias compared to these other techniques .
We also derive an empirical relation between the cluster mass and the galaxy velocity dispersion , M _ { 200 } = 9.6 \times 10 ^ { 14 } \times ( \sigma _ { v } / 1000 km/s ) ^ { 2.7 } / E ( z ) h ^ { -1 } M _ { \odot } , which is in reasonable agreement with the prediction of N -body simulations in the \Lambda CDM cosmology .