We present mass reconstructions from weak lensing for the galaxy clusters A1835 and A2204 over 34 \arcmin \times 34 \arcmin fields using data from the ESO/MPG Wide Field Imager .
Using a background galaxy population of 22 < R < 25.5 we detect the gravitational shear of A1835 at 8.8 \sigma significance , and obtain best-fit mass profiles of \sigma _ { v } = 1233 ^ { +66 } _ { -70 } km/s for a singular isothermal sphere model and r _ { 200 } = 1550 h ^ { -1 } kpc , c = 2.96 for a ‘ universal ’ CDM profile .
Using a color-selected background galaxy population of 22 < R < 25.8 we detect the gravitational shear of A2204 at 7.2 \sigma significance , and obtain best-fit mass profiles of \sigma _ { v } = 1035 ^ { +65 } _ { -71 } km/s for a SIS model and r _ { 200 } = 1310 h ^ { -1 } km/s , c = 6.3 for a ‘ universal ’ CDM profile .
The gravitational shear at distances greater than 10 \arcmin is significantly detected for both clusters .
The best fit weak lensing cluster masses agree well with both X-ray and dynamical mass measurements , although the central concentration of A1835 is much lower in the weak lensing mass profile than that measured by recent Chandra results .
We suggest that this lower concentration is most likely a combination of contamination of the ’ background ’ galaxy population with cluster dwarf galaxies and the effect of a prolate or tri-axial cluster core with the major axis lying near the plane of the sky .
We also detect a number of additional structures at moderate significance , some of which appear to be sub-haloes associated with the clusters .