NEUTRALUNIVERSEMACHINE: How filaments and dark-matter haloes influence the galaxy’s cold gas content

Aims. We aim to investigate the influence of the distance to filaments and dark-matter haloes on galaxy cold-gas content in the empirical model N EUTRAL U NIVERSE M ACHINE (NUM) and the hydrodynamical simulation IllustrisTNG. Methods. We used DisPerSE to identify cosmic web structures and calculate the distance of galaxies to filaments for both observations and models. We show the results of the H I and H 2 mass functions, H I - and H 2 -halo-mass relations, H I - and H 2 -stellar-mass relations for galaxies in the NUM model and IllustrisTNG with different distances to filaments and compare them with observational measurements. We also show the evolution of H I and H 2 mass densities at different distances to filament bins. Results. We find that how filaments affect the H I gas is generally less significant compared to the halo environment. There is a weak trend in the observations at z = 0 that low-mass haloes lying closer to the filaments tend to have reduced H I masses. However, this trend reverses for massive haloes with log( M vir / M ⊙ ) > 12.5. This behaviour is accurately reproduced in the NUM model due to the dependence of H I gas on the halo formation time, but it does not appear in IllustrisTNG. The influence of filaments on the H I gas becomes slightly weaker at higher redshifts and is only significant for galaxies that reside in massive haloes in the NUM model. Filaments have almost no impact on the H 2 -stellar-mass relation in both models, confirming that H 2 is primarily determined by the galaxy stellar mass and star formation rate.