Group and Field Galaxy Catalogs in TNG100: Assembly Bias and Gas Depletion

Abstract

We investigate the impact of the group environment on galaxy properties using the TNG100-1 simulation at z = 0. Analyzing 4,424 galaxies in 544 groups and 6,561 field galaxies (9.0 ≤log10(M⋆/M⊙) ≤ 12.0), we find that the Galaxy Stellar Mass Function (GSMF) is best described by a double-Schechter model across environments. Group members exhibit a higher mass than field counterparts, indicating environmental suppression of intermediate-mass satellites. Merger history analysis shows that single Brightest Group Galaxies (BGGs) experience twice as many mergers as BGGs in groups with multiple or no distinct centrals. While merger counts correlate with group richness and BGG stellar mass, they show no significant relationship with the r-band magnitude gap (Δm21). This implies that Δm21 encodes complementary information on halo assembly history, consistent with assembly bias. Finally, group satellites exhibit a mass-independent neutral hydrogen (H i) deficit of ∼ 0.4 dex relative to the field, which increases to ∼ 1.0 dex for BGGs with M⋆ >∼1010.5M⊙.