On-line Workshop, June 14-18, 2021

Proto-clusters, high redshift galaxy clusters, and merging clusters represent the initial stages in the formation of largest gravitationally-bound structures in the Universe. Forming via mergers and accretion, (proto-)cluster assembly has a decisive impact on their subsequent evolution, and is thus an important process to understand. The aim of GCF2021 is to discuss cluster formation over the last roughly ten billion years, from its beginnings to the present day, with a particular focus on the progress and developments since our first GCF meeting in 2017.

This is a golden age to study assembling clusters and proto-clusters. Several new facilities covering the entire electromagnetic spectrum have just been completed, are being commissioned now, or are in the advanced planning phase.

Key questions the meeting will address include:

• How do we define proto-clusters? 
• What distinguishes them from clusters? 
• How reliably do we detect and select merging clusters and proto-clusters?
• When does the hot intra-cluster medium form?
• How does the formation of (proto-)clusters relate to the peak of star formation and black hole activity?
• What new facilities are needed to advance the study of cluster/proto-cluster assembly?

This is truly a multi-wavelength topic and participants with expertise from the full span of the electromagnetic spectrum are encouraged to contribute. 

*Figure 1: “Simulation of a proto-cluster at z~2.5 found in DIAGONA (Bassini et al. 2020, Astronomy & Astrophysics, Volume 642, id.A37, 19 pp.). Image was produced by Alex Saro using the Splotch code (Dolag et al. 2008; New Journal of Physics, Volume 10, Issue 12, id. 125006 (2008))”