Deep Chandra X-Ray Observations of A2029: The Merger History of a Relaxed, Strong Cool Core Cluster

Abstract We present results from very deep (485 ks) Chandra X-ray observations of the relaxed, cool core cluster A2029 ( z = 0.0767). A2029 hosts one of the longest, most continuous sloshing spirals ever observed, which we find extends nearly 600 kpc from the cluster core. In addition to providing detailed views of the sloshing spiral, imaging and spectroscopic analysis reveals intracluster medium (ICM) substructure related to the merger history, including a broad “splash” of cooler gas and a potential merger shock. The radio lobes of the central WAT source show evidence of alignment with the sloshing motions, consistent with ICM bulk flow, rather than host-galaxy motion, as the primary driver of lobe bending. Comparison to a 1:10 mass-ratio off-axis merger simulation indicates that the observed ICM structures are relics of a second core passage of a subcluster ∼4 Gyr after the start of the merger, where the “splash” feature is revealed to be a wake of cool gas trailing behind the subcluster. Overall, our results suggest that A2029 is still settling from past interactions—showing that even the initially most relaxed-looking clusters can be hiding a rich history of dynamical activity.