WEAVE Observations Reveal Shock-Driven Emission in Jellyfish Tails

As galaxies fall under gravity into groups and clusters, they are exposed to a range of violent processes unique to dense environments. Of particular interest is ram pressure, an environmental mechanism that, when powerful enough, can strip a galaxy of its star-forming gas, effectively shutting down its star formation. Remarkably, the existing stellar population is largely unaffected. Galaxies undergoing strong, active ram pressure stripping (RPS) are known as jellyfish galaxies, named for the dramatic tails of stripped gas that trail behind them.

The Coma Legacy IFU Survey (CLIFS), led by Dr. Ian Roberts at the University of Waterloo (Canada), will observe all 29 star-forming galaxies in the Coma Cluster with radio continuum tails, along with a comparison sample of "normal" star-forming galaxies using the WEAVE Large-IFU mode. The Coma Cluster provides an ideal laboratory for studying RPS: it is the nearest massive galaxy cluster and contains an unusually high fraction of jellyfish galaxies, likely due to its high halo mass and ongoing subgroup merger activity.

The CLIFS team is particularly interested in studying emission from jellyfish tails. Previous studies have found evidence for ongoing star formation in the tails, but many such samples were identified based on the presence of extra-planar star-forming knots, possibly introducing a selection bias. In contrast, the CLIFS sample was not selected based on the basis of extra-planar star formation and thus provides a powerful way to constrain how common star formation is, in stripped gas tails.

Using a preliminary sample of five jellyfish galaxies, McMaster University (Ontario, Canada) PhD candidate Lauren Foster and collaborators compared Hα emission from WEAVE and 144 MHz radio continuum emission from LOFAR in both galaxy disks and tails. While both tracers typically track star formation, radio emission can be boosted if cosmic rays are accelerated by other processes. The team found that the two tracers agree well in galaxy disks, but that radio-derived star formation rates are much higher in the tails than the Hα-derived values, indicating that star formation is not the dominant source of tail emission.

The CLIFS team takes advantage of the wide spectral range and large field of view provided by WEAVE to determine spatially-resolved emission-line diagnostics and gas kinematics for the stripped material. They find that the stripped gas in the jellyfish tails is excited by shocks driven by ram pressure. This work is just one piece of the broader CLIFS effort. The complete sample will allow the team to fully constrain the fraction of radio tails with active star formation in Coma, as well as spatially resolve star-formation histories across stripped galaxy disks.

About WEAVE

WEAVE is a powerful, next-generation multi-fibre spectrograph on the WHT. It uses optical fibres to gather light from celestial sources and transmits it to a two-arm spectrograph, and records them on large-format CCD light detectors. The raw data are transferred over the internet to computers at the Cambridge Centre of Excellence for Astronomical Data (CamCEAD) and the Instituto de Astroífisica de Canarias (IAC), and the science-ready products are stored in an archive at the facilities of the Telescopio Nazionale Galileo (TNG, operated by FGG for INAF) at the Roque de Los Muchachos Observatory, Spain.

WEAVE's versatility is one of its biggest strengths. While the LIFU mode hosts 547 fibres closely-packed to image extended areas of the sky, in the MOS mode up to 960 individual fibres can be separately positioned using two robots to gather light from many hundreds of stars, galaxies or quasars. In the mIFU mode, the fibres are organised into 20 units, each consisting of 37 fibres, that are used to study small extended targets such as nebulae and distant galaxies. Read more at WEAVE - Instrument Overview.

Funding for the WEAVE facility has been provided by UKRI STFC, the University of Oxford, NOVA, NWO, Instituto de Astrofísica de Canarias (IAC), the Isaac Newton Group partners (UKRI STFC, NWO, and Spain, led by the IAC), INAF, CNRS-INSU, the Observatoire de Paris, Région Îlele-de-France, CONACYT through INAOE, the Ministry of Education, Science and Sports of the Republic of Lithuania, Konkoly Observatory (CSFK), Max-Planck-Institut fÃ¼r Astronomie (MPIA Heidelberg), Lund University, the Leibniz Institute for Astrophysics Potsdam (AIP), the Swedish Research Council, the European Commission, and the University of Pennsylvania. The WEAVE Survey Consortium consists of the ING, its three partners, represented by UKRI STFC, NWO, and the IAC, NOVA, INAF, GEPI, INAOE, Vilnius University, FTMC â€“ Center for Physical Sciences and Technology (Vilnius), and individual WEAVE Participants. The WEAVE-project website can be found at https://weave-project.atlassian.net/wiki/display/WEAVE and the full list of granting agencies and grants supporting WEAVE can be found at https://weave-project.atlassian.net/wiki/display/WEAVE/WEAVE+Acknowledgements.

About the William Herschel Telescope

The Willliam Herschel Telescope (WHT) is operated on the island of La Palma (Canary Islands, Spain) by the Isaac Newton Group of Telescopes (ING) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC). The ING is funded by the Science and Technology Facilities Council (STFC-UKRI) of the United Kingdom, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands, and the IAC in Spain. The IAC's contribution to the ING is funded by the Spanish Ministry of Science, Innovation and Universities.

Research paper

Foster, Lauren et al., 2026, "Early Results from the Coma Legacy IFU Survey (CLIFS): Ram Pressure Induced Shocks and Ionization in Jellyfish Tails", ApJ, 999, 164 [ Paper ].

Science contact

Dr Ian Roberts
Waterloo Centre for Astrophysics, Canada
ianruwaterloo.ca

Media contact

Javier Méndez
ING PR Officer
Email: outreaching.iac.es