1112.3659 (Kaylea Nelson et al.)

Evolution of the Merger Induced Hydrostatic Mass Bias in Galaxy Clusters    [PDF]

Kaylea Nelson, Douglas H. Rudd, Laurie Shaw, Daisuke Nagai

In this work, we examine the effects of mergers on the hydrostatic mass estimate of galaxy clusters using high-resolution Eulerian cosmological simulations. We utilize merger trees to isolate the last major merger for each cluster in our sample and follow the time evolution of the hydrostatic mass bias as the systems relax. This approach enables us to characterize the dynamical state of clusters more robustly and quantitatively than morphological classification. We find that during a major merger, a shock propagates outward from the parent cluster, resulting in a large overestimate in the hydrostatic mass bias. After the merger, as a cluster relaxes, the bias in hydrostatic mass estimate decreases but remains at a level of 5-10% with 15-20% scatter. We also investigate the post-merger evolution of the non-thermal pressure support, a dominant cause of this residual mass bias. At r500, the contribution from non-thermal pressure support peaks at 30% of the total pressure during the merger and quickly decays to ~10-15% as a cluster relaxes. Additionally, we use a measure of the non-thermal pressure to correct the hydrostatic mass estimate. We discover that 4 Gyr after major mergers, the direct effects of the merger event on the hydrostatic mass bias have become negligible. Thereafter, the mass bias is primarily due to residual bulk motions in the gas which are not accounted for in the hydrostatic equilibrium equation. We present a hydrostatic mass bias correction method that can recover the unbiased cluster mass with 8% scatter at r500 and 11% scatter in the outskirts, within r200.

View original: http://arxiv.org/abs/1112.3659