Galaxy Cluster Formation II (GCF 2021) - Virtual Workshop

14-18 June 2021

Galaxy Cluster Formation II:

Mergers, Protoclusters, and Star Formation in Overdense Environments

Registration is free to all participants. However, to facilitate discussions the number of participants will be limited to 200.

The workshop will be held online.

The aim of this conference is discuss the beginnings and formation of the largest gravitationally-bound structures in the Universe.


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. 


The conference is scheduled to take place online (as a  Zoom meeting), for 4 hours each day of the program. We anticipate the live program to start at 11:30 UTC and finish at 16:30 UTC. Besides invited review talks, the conference will include contributed talks and posters and time allocated for discussions and social interactions. The talks (but not the discussion)* will be recorded and uploaded to the conference Youtube channel within 24 h. Virtual coffee breaks will take place on The conference will have a dedicated Slack workspace to foster discussions and post files (posters and relevant papers). We anticipate discussion on Slack to start at least 1 week before the conference. After the conference, slides and posters will be uploaded to Zenodo​​ to create a permanent record of the workshop that is also indexed by ADS. 

* This is intentional. We do not wish to discourage any scientists, including students, from participation in the discussion.

ESO Code of Conduct:

We aim to host a friendly and productive meeting which is welcoming for everyone. As such, we ask all participants to adhere to the ESO Conference Code of Conduct.  In summary:

  1. Behave professionally. Harassment and sexist, racist, or exclusionary comments or jokes are not appropriate. Harassment includes sustained disruption of talks or other events, inappropriate physical contact, sexual attention or innuendo, deliberate intimidation, stalking, and photography or recording of an individual without consent. It also includes offensive comments related to individual characteristics, for example: age, gender, sexual orientation, disability, physical appearance, race, nationality or religion.
  2. All communication should be appropriate for a professional audience including people of many different backgrounds. Sexual or sexist language and imagery is not appropriate.
  3. Be respectful and do not insult or put down other attendees or facilitators of the event. Critique ideas not people.
  4. Should a participant witness events of bullying, harassment or aggression, we recommend that they approach the affected person to show support and check how they are. The witness may also wish to suggest that the person report the inappropriate behaviour. However, it is up to the affected person alone whether or not they wish to report it.
  5. If participants wish to share photos of a speaker on social media, we strongly recommend that they first get the speaker’s permission. Participants may also share the contents of talks/slides via social media unless speakers have asked that specific details/slides not be shared.

GCF 2021 channels on

This workshop is supported by ESO and the Smithsonian Astrophysical Observatory.

Keywords: merging clusters | high-z clusters | proto-clusters | detection, classification & comparison | ICM physics | AGN feedback | star formation | galaxy evolution | future facilities

Workshop email: