The Zurich Environmental Study (ZENS) of galaxies in groups along the cosmic web. V. properties and frequency of merging satellites and centrals in different environments

We use the Zurich Environmental Study database to investigate the environmental dependence of themerger fraction Γ and merging galaxy properties in a sample of∼1300 group galaxies withM > 10 M⊙ and 0.05 < z < 0.0585. In all galaxy mass bins investigated in our study, we find that Γ decreases by a factor of ∼2–3 in groups with halo masses MHALO > 10 13.5 M⊙ relative to less massive systems, indicating a suppression of merger activity in large potential wells. In the fiducial case of relaxed groups only, we measure a variation of ∆Γ/∆ log(MHALO) ∼ −0.07 dex, which is almost independent of galaxy mass and merger stage. At galaxy masses >10 M⊙, most mergers are dry accretions of quenched satellites onto quenched centrals, leading to a strong increase of Γ with decreasing group-centric distance at thesemass scales. Both satellite and central galaxies in these high-massmergers do not differ in color and structural properties from a control sample of nonmerging galaxies of equal mass and rank. At galaxy masses of <10 M⊙ where we mostly probe satellite–satellite pairs and mergers between star-forming systems close pairs (projected distance <10–20 kpc) show instead ∼2× enhanced (specific) star formation rates and ∼1.5× larger sizes than similar mass, nonmerging satellites. The increase in both size and star formation rate leads to similar surface star formation densities in the merging and control-sample satellite populations.