From BCGs to cosmic filaments, from AGNi to merger shocks: multi-scale and multi-phase galaxy cluster evolution in X-rays

Hundreds of galaxies embedded in a hot and tenuous intracluster medium (ICM), all bound by the deep gravitational potential well of Dark Matter (DM). Today, we have a front seat to observe “what” galaxy clusters (GCs) have become. The “how” part is enclosed within the ICM thanks to this DM potential, keeping a log of past activity within the cluster. From the feeding and feedback of the central active galactic nucleus (AGN) to cluster mergers, from the brightest cluster galaxy (BCG) evolution to GC - cosmic filament interactions; GCs host all observable astrophysical processes. We do not have a complete picture of the processes that shape the GCs yet, but X-ray observations hold a key piece to solve this evolutionary puzzle. While thermal ICM shines brightly in X-rays, non-thermal processes are exposed in radio and in hard X-rays, emphasizing the importance of multi-wavelength studies.

In this talk, I will present a variety of multi-phase and multi-scale research on galaxy cluster evolution. I will share our findings from NuSTAR, Chandra, XMM-Newton and Suzaku X-ray data of three GCs as well as their radio and optical clues, and introduce our methods that defy the limitations of our observatories. Firstly, I will discuss a BCG corona and its AGN activity in a non-cool-core GC, MKW 08, and the BCG-GC coevolution. I will present our method to resolve the ICM/interstellar medium (ISM) both spectrally and spatially at the interface. I will then discuss the case of a merging GC, CL 0217+70, where we discovered secondary shocks within 0.6 r₅₀₀ that may be sustaining its giant radio halo. Within this context, I will present a new cross-talk method we used to obtain the most accurate temperature measurements with NuSTAR. I will finally discuss the merging GC, A3395, which is not only going through a merger within, but also interacting with A3391 via a cosmic filament, and I will conclude my talk with the brief description of our scattered light background reduction method used for analyzing off-center NuSTAR observations.