MEASURING DARK MATTER ELLIPTICITY OF A901/902 USING PARTICLE-BASED LENSING

We present a non-parametric measure of the ellipticity and the alignment of the dark matter halos in the A901/902 supercluster. This supercluster is a system of four separate peaks in a 0 degrees.5 x 0 degrees.5 field of view. We map the mass distribution of each individual peak using an improved version of Particle-Based Lensing (PBL) and measure the ellipticity of the dark matter halos associated with two of the peaks directly from the mass map and by fitting them to a singular isothermal ellipse. The parametric and non-parametric measurements are consistent for A901b while the position angle for the Southwest Group is different for the two techniques. We account for this discrepancy to substructure present in the Southwest Peak. We estimate an axis ratio of 0.37 +/- 0.1 for A901b and 0.54(-0.09)(+ 0.08) for the Southwest Group.