Caught in the web: Galaxy mergers along cosmic filaments

Context. Galaxy clusters grow through the accretion of galaxies from groups, filaments, and other clusters. During this process, galaxies may undergo pre-processing in lower density environments, where galaxy–galaxy mergers and other interactions can significantly alter their properties prior to cluster infall. Aims. We investigate the role of galaxy mergers in the pre-processing of galaxies prior to cluster infall by studying the spatial distribution of galaxy mergers across the cosmic web. Methods. We used a sample of 43 922 galaxies being targeted by the 4MOST CHANCES survey in and around 33 low-redshift clusters ( z < 0.07). Using Zoobot, a deep-learning framework trained on Galaxy Zoo data, we identified 698 galaxy mergers. We measured their distances to cosmic web filaments and compared those results to those of non-merging galaxies. Results. We find that galaxy mergers are significantly closer to filaments than the non-merging galaxy population, with this trend being strongest beyond the cluster virial radius. This suggests that filaments provide conditions conducive to mergers, possibly moderating relative velocities and enhancing gas availability. Conclusions. Our findings support a scenario in which filaments play a key role in transforming (pre-processing) galaxies by promoting mergers before entering the cluster cores where star formation is quenched.