Measuring the surface mass density ellipticity of redMaPPer galaxy clusters using weak-lensing

ELIZABETH JOHANA GONZALEZ; MARTÍN MAKLER; DIEGO GARCÍA LAMBAS; MARTÍN CHALELA; MARÍA PEREIRA; LUDOVIC VAN WAERBEKE; HUANYUAN SHAN

Encuentro; EUROPEAN ASTRONOMICAL SOCIETY ANNUAL MEETING; 2020

Galaxy clusters are expected to reside on highly overdense dark matter halos, which according to numerical simulations, can be well described by a triaxial model and appears elliptical in projection. In this work we constrain the average projected halo ellipticity of a sample of redMaPPer clusters (0.2 < z < 0.4) using weak-lensing stacking techniques. For the analysis we combine shear catalogs from four weak lensing surveys (KiDS/KV450, CFHTLenS, CS82, and RCSLenS). In order to estimate the major semi-axis orientation of the halos, we assume that the dark matter can be well traced by the satellite distribution. Taking this into account we compute the position angle for each redMapper cluster according to the quadrupole moments. We consider different proxies to estimate the orientation taking into account different weights for computing the quadrupole moments and a cut in the membership probability. The surface density is modelled considering a multipole expansion from which the shear components can be decomposed into the monopole and quadrupole contributions, where the quadrupole is proportional to the projected ellipticity. We derive the aligned component of the projected halo ellipticity by fitting both quadrupole component profiles, tangential and cross, within a projected distance of 100kpc < r < 5Mpc. We also study the relation between the derived projected ellipticity and the average cluster mass and redshift. Finally, we analyse the impact of misscentring in the ellipticity estimates. For the whole sample we obtain, with more than 5\sigma detection level, a median halo ellipticity of 0.17 +/- 0.03 by aligning the halos according to the distribution of all the galaxies classified as members.