Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET)

¹ INAF – Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122, Padova, Italy
² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131, Trieste, Italy
³ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151, Trieste, Italy
⁴ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047, Selargius, (CA), Italy
⁵ Tianjin Normal University, Binshuixidao 393, 300387, Tianjin, China
⁶ Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, Sydney, NSW, 2006, Australia
⁷ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
⁸ Instituto de Radioastronomía y Astrofísica, UNAM, Campus Morelia, A.P. 3-72, C.P. 58089, Morelia, Mexico
⁹ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, Via Alfonso Corti 12, 20133, Milano, Italy
¹⁰ Department of Physics, Informatics and Mathematics, University of Modena and Reggio Emilia, 41125, Modena, Italy
¹¹ Institute of Physics, GalSpec Laboratory, EPFL, Observatoire de Sauverny, Chemin Pegasi 51, CH-1290, Versoix, Switzerland
¹² Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
¹³ Millennium Nucleus for Galaxies (MINGAL), Chile
¹⁴ Centre for Radio Astronomy Techniques and Technologies (RATT), Department of Physics and Electronics, Rhodes University, Makhanda, 6140, South Africa
¹⁵ South African Radio Astronomy Observatory, Cape Town, 7925, South Africa
¹⁶ INAF – Astronomical Observatory of Capodimonte, Salita Moiariello 16, I-80131, Naples, Italy
¹⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA, 02138, USA
¹⁸ School of Physics, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
¹⁹ School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK
²⁰ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa
²¹ Flatiron Institute, Center for Computational Astrophysics, 162 5th Avenue, New York, NY, 10010, USA
²² Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV, Groningen, The Netherlands

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

Received: 18 November 2025
Accepted: 26 February 2026

Abstract

Galaxy evolution is profoundly shaped by intricate internal and external mechanisms that regulate the baryon cycle and star formation activity. To characterize the role of these processes as a function of galaxy environment, we present a theoretical framework based on the GAlaxy Evolution and Assembly (GAEA) semi-analytic model. We extracted portions of simulated volumes that include isolated galaxies, pairs, group, and filament members at z ∼ 0, specifically avoiding massive clusters. Galaxies were classified using both intrinsic (halo-based) and observational (2D projected) parameterizations, reconstructing their environmental histories from z = 2 and identifying mergers, tidal interactions, ram pressure stripping (RPS), and starvation. GAEA predictions show that 2D information biases environment definitions, decreasing isolated and group fractions, while doubling pairs. More than half of galaxies remain unaffected by the investigated processes since z = 2. Among the galaxies affected by external mechanisms, mergers dominate at high stellar masses (40−60% at log(M_*/M_⊙) > 10.5). Tidal interactions are less frequent and their incidence increases with stellar mass (up to 20%). RPS dominates in groups and filaments at intermediate masses (∼50%), while starvation ranges from 20 to 30%. The incidence of the different mechanisms depends strongly on both mass and environment, although their imprints on global properties (e.g., colors, gas fractions, sizes) are often subtle. Quenched fractions rise steadily from isolated galaxies to groups. Distinct evolutionary pathways emerge: at low masses (log(M_*/M_⊙) < 9.5), galaxies in groups and filaments exhibit a faster mass growth than galaxies in other environments, especially those undergoing starvation, mergers, and (to a lesser extent) RPS. The differences are less significant when moving to higher masses, where no clear dependence on any physical mechanism emerges, despite the fact that at these masses, a clear star formation suppression is evident in mergers and starved galaxies. This theoretical investigation provides essential context for the recently initiated multiwavelength program Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET), introduced here for the first time.