How galaxy properties vary with filament proximity in the SIMBA simulations

Abstract

We explore the dependence of global galaxy properties in the SIMBA simulation as a function of distance from filaments identified using DisPerSe. We exclude halos with mass $M_h>10^{13}M_\odot$ to mitigate the impact of group and cluster environments. Galaxies near filaments are more massive and have more satellites, which we control for by examining deviations from best-fit scaling relations. At $z=0$, star formation (SF) is significantly suppressed within $\lesssim 100$ kpc of filaments, more strongly for satellites, indicating substantial pre-processing in filaments. By $z=2$, the trend is weak and if anything indicates an increase in SF activity close to filaments. The suppression at $z\lesssim 1$ is accompanied by lowered \HI fractions, and increased metallicities, quenched fractions, and dispersion-dominated systems. $H_2$ fractions are not strongly suppressed when controlling for stellar mass, suggesting that star formation efficiency drives the drop in SF. By comparing amongst different SIMBA feedback variant runs, we show that the majority of SF suppression owes to filamentary shock-heating, but there is a non-trivial additional effect from AGN feedback. When looking around massive ($M_h>10^{13}M_\odot$) halos, those galaxies near filaments behave somewhat differently, indicating that filaments provide an additional environmental effect relative to halos. Finally, we compare SIMBA results to EAGLE and IllustrisTNG at $z=0$, showing that all models predict SF suppression within $\lesssim 100$ kpc of filaments, nonetheless, detailed differences may be observationally testable.