The Observable Thermal and Kinetic Sunyaev-Zel'dovich Effect in Merging Galaxy Clusters

TL;DR

This paper uses high-resolution simulations to study the thermal and kinetic Sunyaev-Zel'dovich effects in merging galaxy clusters, revealing how mergers influence observable SZE features and the potential for probing cluster dynamics.

Contribution

It presents the first detailed simulation of the combined thermal and kinetic SZE in a massive merging galaxy cluster, highlighting the impact of mergers on SZE signals and velocity measurements.

Findings

kSZ can dominate over tSZ at certain frequencies and projections

Merger shocks produce extended features visible in mock SZE images

Velocity estimation biases are around 10% due to line-of-sight effects

Abstract

The advent of high-resolution imaging of galaxy clusters using the Sunyaev-Zel'dovich Effect (SZE) provides a unique probe of the astrophysics of the intracluster medium (ICM) out to high redshifts. To investigate the effects of cluster mergers on resolved SZE images, we present a high-resolution cosmological simulation of a 1.5E15 M_sun adiabatic cluster using the TreeSPH code ChaNGa. This massive cluster undergoes a 10:3:1 ratio triple merger accompanied by a dramatic rise in its integrated Compton-Y, peaking at z = 0.05. By modeling the thermal SZE (tSZ) and kinetic SZE (kSZ) spectral distortions of the Cosmic Microwave Background (CMB) at this redshift with relativistic corrections, we produce various mock images of the cluster at frequencies and resolutions achievable with current high-resolution SZE instruments. The two gravitationally-bound merging subclusters account for 10% and 1% of the main cluster's integrated Compton-Y, and have extended merger shock features in the background ICM visible in our mock images. We show that along certain projections and at specific frequencies, the kSZ CMB intensity distortion can dominate over the tSZ due to the large line of sight velocities of the subcluster gas and the unique frequency-dependence of these effects. We estimate that a one-velocity assumption in estimation of line of sight velocities of the merging subclusters from the kSZ induces a bias of ~10%. This velocity bias is small relative to other sources of uncertainty in observations, partially due to helpful bulk motions in the background ICM induced by the merger. Our results show that high-resolution SZE observations, which have recently detected strong kSZ signals in subclusters of merging systems, can robustly probe the dynamical as well as the thermal state of the ICM.