The Dark Matter Radial Profile in the Core of the Relaxed Cluster A2589

We present an analysis of a Chandra ACIS observation of the galaxy cluster A2589 to constrain the radial distribution of the total gravitating matter and the dark matter in the core of the cluster. A2589 is especially well suited for this analysis, because the hot gas in its core region (r ≲ 0.1rvir) is undisturbed by interactions with a central radio source. From the largest radius probed (r = 0.07rvir) down to r ≈ 0.02rvir, dark matter dominates the gravitating mass. Over this region, the radial profiles of the gravitating and dark matter are fitted well by the Navarro-Frenk-White (NFW) and Hernquist profiles predicted by cold dark matter (CDM). The density profiles are also described well by power laws, ρ ∝ r-α, where α = 1.37 ± 0.14 for the gravitating matter and α = 1.35 ± 0.21 for the dark matter. These values are consistent with profiles of CDM halos but are significantly larger than the α ≈ 0.5 found in low surface brightness galaxies and expected from self-interacting dark matter models.