Letter to the Editor

Caught in the web: Galaxy mergers along cosmic filaments

¹ Universidad de Concepción, Víctor Lamas 1290, Barrio Universitario, Concepción, Chile
² Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
³ Millennium Nucleus for Galaxies (MINGAL), Valparaíso, Chile
⁴ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile
⁵ Departamento de Astronomía, Universidad de La Serena, Avda. Raúl Bitrán 1305, La Serena, Chile
⁶ Instituto de Astronomía y Ciencias Planetarias (INCT), Universidad de Atacama, Copayapu 485, Copiapó, Chile
⁷ Departamento de Física Teórica y del Cosmos, Edificio Mecenas, Campus Fuentenueva, Universidad de Granada, E-18071, Granada, Spain
⁸ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071, Granada, Spain
⁹ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
¹⁰ Centre of Excellence for Data Science, Artificial Intelligence & Modelling, The University of Hull, Cottingham Road, Kingston-Upon-Hull, HU6 7RX, UK
¹¹ Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, Rio de Janeiro, RJ, Brazil
¹² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, United Kingdom
¹³ Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2, 00560, Helsinki, Finland
¹⁴ School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
¹⁵ INAF–Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80134, Napoli, Italy
¹⁶ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil
¹⁷ Institute of Astrophysics, Facultad de Ciencias Exactas, Universidad Andrés Bello, Sede Concepción, Talcahuano, Chile
¹⁸ Escola Politécnica, Universidade de São Paulo, Av. Prof. Luciano Gualberto, Travessa do Politécnico 380, São Paulo, Brazil
¹⁹ Max-Planck-Institut für Extraterrestrische Physik (MPE), Gießenbachstraße 1, D-85748, Garching bei München, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 9 November 2025
Accepted: 4 March 2026

Abstract

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.