  We present a novel method for identifying cosmic web filaments using the
IllustrisTNG (TNG100) cosmological simulations and investigate the impact of
filaments on galaxies. We compare the use of cosmic density field estimates
from the Delaunay Tessellation Field Estimator (DTFE) and the Monte Carlo
Physarum Machine (MCPM), which is inspired by the slime mold organism, in the
DisPerSE structure identification framework. The MCPM-based reconstruction
identifies filaments with higher fidelity, finding more low-prominence/diffuse
filaments and better tracing the true underlying matter distribution than the
DTFE-based reconstruction. Using our new filament catalogs, we find that most
galaxies are located within 1.5-2.5 Mpc of a filamentary spine, with little
change in the median specific star formation rate and the median galactic gas
fraction with distance to the nearest filament. Instead, we introduce the
filament line density, Sigma_fil(MCPM), as the total MCPM overdensity per unit
length of a local filament segment, and find that this parameter is a superior
predictor of galactic gas supply and quenching. Our results indicate that most
galaxies are quenched and gas-poor near high-line density filaments at z<=1. At
z=0, quenching in log(M*/Msun)>10.5 galaxies is mainly driven by mass, while
lower-mass galaxies are significantly affected by the filament line density. In
high-line density filaments, satellites are strongly quenched, whereas centrals
have reduced star formation, but not gas fraction, at z<=0.5. We discuss the
prospect of applying our new filament identification method to galaxy surveys
with SDSS, DESI, Subaru PFS, etc. to elucidate the effect of large-scale
structure on galaxy formation.
