Abstract
In this work, we study the shape of the projected surface mass density distribution of galaxy clusters using weak-lensing stacking techniques. In particular, we constrain the average aligned component of the projected ellipticity, epsilon, for a sample of redMaPPer clusters (0.1 <= z < 0.4). We consider six different proxies for the cluster orientation and measure epsilon for three ranges of projected distances from the cluster centres. The mass distribution in the inner region (up to 700kpc) is better traced by the cluster galaxies with a higher membership probability, while the outer region (from 700kpc up to 5Mpc) is better traced by the inclusion of less probable galaxy cluster members. The fitted ellipticity in the inner region is epsilon = 0.21 +/- 0.04, in agreement with previous estimates. We also study the relation between epsilon and the cluster mean redshift and richness. By splitting the sample in two redshift ranges according to the median redshift, we obtain larger epsilon values for clusters at higher redshifts, consistent with the expectation from simulations. In addition, we obtain higher ellipticity values in the outer region of clusters at low redshifts. We discuss several systematic effects that might affect the measured lensing ellipticities and their relation to the derived ellipticity of the mass distribution.