Work

Fishing for Jellyfish Galaxies

Year: 2026

Type: article

Abstract: Aims. We present the first results of Fishing for Jellyfish Galaxies , a pilot citizen-science project using Zooniverse to identify galaxies undergoing ram-pressure stripping (RPS). Methods. Volunteers visually inspected colour images of late-type galaxies from the Dark Energy Camera Legacy Survey. The sample consisted of 49 703 galaxies selected within 4 × R 500 of clusters and groups, restricted to those brighter than 19th magnitude in the g and r bands, and with a minimum half-light radius of 2 arc seconds, to aid classification. We detail our data processing, including debiasing classifications and optimising vote-fraction thresholds to maximise completeness and purity, calibrated against a ground-truth set of pre-labelled galaxies. Results. Our final catalogue contains 6739 jellyfish candidates (6621 new), 5430 merger candidates, and 29 729 undisturbed galaxies, with 3910 jellyfish exhibiting prominent tail-like morphologies. We find that the fraction of RPS candidates rises from ∼10% in galaxy groups to ∼20–30% in massive clusters, confirming the findings of previous studies carried out on smaller samples. For the subset of our RPS candidate sample with spectroscopic data, we measure a median cluster-centric velocity 53% higher than the general cluster population, consistent with galaxies in early stages of accretion into the cluster. They are also typically late-type blue galaxies with elevated star-formation rates, in agreement with expectations. These results demonstrate that citizen scientists can reliably identify galaxies that undergo environmental processes. We provide the initial release of 37 599 visually classified galaxies as a resource for future studies of galaxy transformation in clusters.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202659056