Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET)

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 similar to 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-circle dot) > 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 (similar to 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-circle dot) < 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.