Effect of asphericity in caustic mass estimates of galaxy clusters

Abstract: The caustic technique for measuring mass profiles of galaxy clusters relies on the assumption of spherical symmetry. When applied to aspherical galaxy clusters, the method yields mass estimates affected by the cluster orientation. Here we employ mock redshift catalogues generated from cosmological simulations to study the effect of clusters intrinsic shape and surrounding filamentary structures on the caustic mass estimates. To this end, we develop a new method for removing perturbations from large-scale structures, modelled as the two-halo term, in a caustic analysis of stacked cluster data. We find that the cluster masses inferred from kinematical data of ~10^14 Msun clusters observed along the major axis are larger than masses from those observed along the minor axis by a factor of 1.7 within the virial radius, increasing to 1.8 within three virial radii. This discrepancy increases by 20% for the most massive clusters. In addition a smaller but still significant mass discrepancy arises when filamentary structures are present near a galaxy cluster. We find that the mean cluster mass from random sightlines is unbiased at all radii and their scatter ranges from 0.14 to 0.17 within one and three virial radii, with a 40% increase for the most massive clusters. We provide tables which estimate the caustic mass bias given observational constraints on the cluster orientation.