Spatial matter density mapping of the STAGES Abell A901/2 supercluster
  field with 3D lensing
  We present weak lensing data from the HST/STAGES survey to study the
three-dimensional spatial distribution of matter and galaxies in the Abell
901/902 supercluster complex. Our method improves over the existing 3D lensing
mapping techniques by calibrating and removing redshift bias and accounting for
the effects of the radial elongation of 3D structures. We also include the
first detailed noise analysis of a 3D lensing map, showing that even with deep
HST quality data, only the most massive structures, for example M200>~10^15
Msun/h at z~0.8, can be resolved in 3D with any reasonable redshift accuracy
(\Delta z~0.15). We compare the lensing map to the stellar mass distribution
and find luminous counterparts for all mass peaks detected with a peak
significance >3\sigma. We see structures in and behind the z=0.165 foreground
supercluster, finding structure directly behind the A901b cluster at z~0.6 and
also behind the SW group at z~0.7. This 3D structure viewed in projection has
no significant impact on recent mass estimates of A901b or the SW group
components SWa and SWb.
