Star-forming galaxies in the cosmic web in the last 11 Gyr

Abstract

We investigate how the star formation activity of galaxies depends on their position within the cosmic web using the SIMBA cosmological simulation from redshift z = 3 to z = 0. While previous studies have found that galaxies closer to filaments tend to be more massive and quenched, it remains unclear whether these trends reflect intrinsic environmental effects or changes in the galaxy population mix. To address this, here we focus exclusively on star-forming galaxies, robustly selected using both the specific star formation rate (sSFR) and gas depletion timescale criteria to isolate the direct impact of the cosmic web on star-forming galaxies. We reconstructed the 3D cosmic web skeleton using DISPERSE and computed each galaxy’s distance to its nearest filament. After explicitly removing the stellar-mass dependence of all quantities, we examined the deviations in star formation rate (SFR), sSFR, molecular and atomic gas depletion timescales, and gas fractions as a function of this distance. We found a clear and redshift-dependent modulation of star formation with filament proximity: at high redshift (z ≳ 2), galaxies closer to filaments show enhanced SFR and gas accretion, reflecting efficient filament-fed growth. At z = 0, we observe a V-shaped trend in the sSFR and depletion timescales, with minima at intermediate distances (∼0.25 cMpc) and a surprising upturn very close to the filament cores, suggesting a resumed accretion in the densest environments. These effects are not driven by mergers and are primarily associated with satellite galaxies at low redshift. Our results demonstrate that large-scale cosmic web proximity modulates star formation in star-forming galaxies through a combination of gas supply regulation and environmental processing, with different mechanisms dominating across cosmic time