Galaxy evolution is complex and involves the interplay of various physical mechanisms, including gravity, gas dynamics, radiation, star formation, feedback from stars and active galactic nuclei (AGN) as well as the influence of dark matter. This is a multiscale mechanism ranging from individual star formation within galaxies up to the clustering of galaxies in cosmic filaments and clusters.

When a galaxy enters a cluster, it begins to lose gas because of the ram pressure of the ambient gas (Gunn & Gott 1972) and tidal forces (tidal stripping). In galaxy clusters, the effect of dynamic pressure dominates (e.g. Simpson et al. 2018). Ram-pressure stripping is documented not only by hydrodynamic simulations (e.g. Steinhauser et al. 2016), but also by the observation of “jellyfish galaxies” (Ebeling et al. 2014, Boselli et al. 2023). The more extensive hot gas is removed first, then it is the turn of the cold atomic gas (Bekki 2009). Molecular gas is very difficult to extract (and resolve in simulations; Hausammann et al. 2019). Often these perturbing mechanisms start to be active in groups of galaxies which fall into a cluster, as suggested by numerical simulations (Haggar et al. 2024, Lokas et al. 2023). In this case, it is the intergalactic gas from the group which will be removed first. Interest in this topic comes from the importance of the environment on the evolution of cluster galaxies and their quenching. Indeed, the impact of ram pressure modifies the star formation histories and chemical abundances of cluster galaxies. Ram pressure could increase the metal content of galaxies if it stops the infall of external gas and, at the same time, it compresses the gas in a way to accelerate star formation inside galaxies (Koutsouridou & Cattaneo 2019). Alternatively, tidal effects can also impact the stellar content in case of encounters and the role of the AGN of the central galaxy on satellites is still uncertain.

The aim of this workshop is to discuss quantitative comparison of simulations/models with observations. What is the current state of the art on the observational side and on the simulation one? Are the simulations capable of accounting for the ram pressure tails observed in jellyfish galaxies? On the observational side, the main questions are the mass of the gas in the ram pressure tails, the length of the tails, the speed of the satellite galaxy and the density of the ambient medium. On the simulation side, several galaxies/groups of galaxies with characteristics similar to the observed sample have been identified. The recent citizen science project named Fishing for Jellyfish project based on IllustrisTNG simulations makes a real breakthrough in the domain (Zinger et al. 2024, Göller et al. 2023, Rohr et al. 2023) with 5307 visually identified jellyfish galaxies. This sample is key to study how to disentangle the different effects in action.

This workshop is supported by the Thematic Action of Cosmology and Galaxies of the CNRS and the Paris Observatory.

- Environmental effect on galaxies

- Ram pressure stripping

- Tidal interaction and mergers

- Groups falling onto clusters

- Multiwavelength observations

- Impact of star-formation and quenching

SOC : Samuel Boissier, Alessandro Boselli, Pavel Jachym, Anne-Laure Melchior

LOC: Andrea Cattaneo, Françoise Combes, Anaëlle Halle, Nathan Meagher, Anne-Laure Melchior, Aashyia Shaji

The workshop will take place in salle du conseil, Observatoire de Paris, 77, avenue Denfert-Rochereau 75014 Paris

Alessandro Boselli (Marseille, France)

Thierry Contini (Toulouse, France)

Dominique Eckert (Geneva, Swizerland)

Alessandro Ignesti (Padova, Italy)

Pavel Jachym (Prag, Czech Republic) 

Aashiya Shaji (Paris, France)

Paolo Serra (Selargius, Italy)

Bernd Vollmer (Strasbourg, France)

Daria Zakharova (Padova, Italy) 

Registrations and abstract submissions up to 18^th March midnight.

Maximum number of participants : 30 persons

The organisers are committed to making this meeting productive and enjoyable for everyone, regardless of gender, sexual orientation, disability, physical appearance, body size, race, nationality or religion. We will not tolerate harassment of participants in any form. Please follow these guidelines:

• Behave professionally. Harassment and sexist, racist, or exclusionary comments or jokes are not appropriate. Harassment includes sustained disruption of talks, sexual attention or innuendo, deliberate intimidation, stalking, and photography or recording of an individual without consent. It also includes offensive comments related to gender, sexual orientation, disability, physical appearance, body size, race or religion.
  
  
• All communication should be appropriate for a professional audience including people of many different backgrounds. Sexual language and imagery is not appropriate.
  
  
• Be kind to others. Do not insult or put down other attendees.

Participants asked to stop any inappropriate behaviour are expected to comply immediately. Attendees violating these rules may be asked to leave the event at the sole discretion of the organisers.

Any participant who wishes to report a violation of this policy is asked to speak, in confidence, to LOC members.

The above has been adapted from the London code of conduct written by Hiranya Peiris and Andrew Pontzen.

Here is the agenda of the workshop (pdf).

Here are the abstracts (pdf).

Anghel Simon

Boselli Alessandro

Cattaneo Andrea

Chilingarian Igor

Combes Françoise

Contini Thierry

Durret Florence

Eckert Dominique

Gray Meghan

Grishin Kirill

Grossova Romana

Hallé Anaëlle

Ignesti Alessandro

Iodice Enrichetta

Jachym Pavel

Mangola Elena Sofia

Meagher Nathan

Melchior Anne-Laure

Salomé Philippe

Serra Paolo

Shaji Aashiya Anitha

Souchereau Harrison

Vollmer Bernd

Zakharova Daria

Participants via zoom : 

Boissier Samuel

Bonnassieux Etienne

Chan Jennifer

Kovakkuni Navyasree

Srbljanović Anežka

Valls-Gabaud David