Constraining the dark matter density in galaxy clusters

Abstract

We illustrate the potential of using stellar velocity dispersion profiles of brightest cluster galaxies (BCGs), in combination with X-ray and weak-lensing derived cluster mass profiles, to constrain the matter distribution from the very centre (1 kpc) to the outskirts (1000 kpc) of galaxy clusters. We have obtained long-slit spectroscopy of a small number of BCGs in CLASH (Cluster Lensing and Supernova Survey with Hubble) clusters at the Southern African Large Telescope (SALT) with the primary goal of measuring their stellar kinematics. The new data extends the observed total mass profile of the cluster over another order of magnitude in radius, which places a much stronger constraint on the dark matter distribution, thereby leveraging the enormous investment in mass-profile measurements at larger radii in these clusters. Here, we discuss the observations and apply the methodology to one of the clusters, RXJ2129.7+0005 (z 0:23), to find results consistent with a mass profile slope that becomes shallower than the typical Navarro-Frenk-White (NFW) profile when dynamical data in the very innermost region of the cluster is also included in its mass profile