Environmental history of filament galaxies

Galaxy properties, such as stellar mass and star formation rate, correlate with their position within the cosmic web. Although galaxy properties can be correlated with a specific environment at a certain cosmic epoch, they may have experienced different environments at previous times. This ‘environmental history’, which is closely linked to pre-processing, is bound to leave an imprint on the observable and physical properties of galaxies. In this work, we use the Galaxy Evolution and Assembly (GAEA) semi-analytic model and the magneto-hydrodynamic IllustrisTNG simulation to reconstruct the environmental histories of galaxies that today reside in filaments between z = 0 and z = 4. Our goal is to understand how galaxy properties are related to their past environments and to uncover the role of the cosmic web in shaping their present-day properties. This approach enables us to determine whether and when filamentary structures influence galaxy evolution. We find that filament galaxies at z = 0 are a heterogeneous mix of populations with distinct environmental histories, and a clear dependency on the infall times into filaments. The vast majority of filament galaxies at z = 0 have experienced group processing at some stage of their evolution, with only ∼20% of galaxies remaining centrals throughout their life. For low-mass filament galaxies (9 < log 10 ( M star / M sun )< 10), both GAEA and TNG100 confirm that environmental effects are primarily driven by group processing: Satellite galaxies in this mass range stop growing stellar mass and exhibit elevated quenched fractions, whereas their central counterparts in filaments have properties that are similar to those of field galaxies. In contrast, massive galaxies (log 10 ( M star / M sun )> 10) are affected by the filament environment, regardless of being centrals or satellites. Massive galaxies that have never been satellites and that entered filaments more than 9 Gyr ago show accelerated stellar mass assembly and higher quenched fractions relative to the field, due to a higher frequency of merger events inside filaments. Moreover, the most massive log(( M star / M sun )> 11) galaxies typically accreted onto filaments over 9 Gyr ago and have never become satellites within a larger halo, highlighting the role of filaments in building up the high-mass end of the galaxy population.