Dissecting the roles of mass and environment quenching in galaxy evolution with EAGLE

We exploit the pioneering cosmological hydrodynamical simulation, EAGLE, to study how the connection between halo mass (M-halo), stellarmass (M-star), and star formation rate (SFR) evolves across redshift. Using principal component analysis, we identify the key axes of correlation between these physical quantities, for the full galaxy sample and split by satellite/central and low/high halo mass. The first principal component of the z = 0 EAGLE galaxy population is a positive correlation between M-halo, M-star and SFR. This component is particularly dominant for central galaxies in low-mass haloes. The second principal component, most significant in high-mass haloes, is a negative correlation betweenMhalo and SFR, indicative of environmental quenching. For galaxies above M-star similar to 10(10) M-circle dot, however, the SFR is seen to decouple from the M-halo-M-star correlation; this result is found to be independent of environment, suggesting that mass quenching effects are also in operation. We find extremely good agreement between the EAGLE principal components and those of Sloan Digital Sky Survey galaxies; this lends confidence to our conclusions. Extending our study to EAGLE galaxies in the range z = 0-4, we find that, although the relative numbers of galaxies in the different subsamples change, their principal components do not change significantly with redshift. This indicates that the physical processes that govern the evolution of galaxies within their dark matter haloes act similarly throughout cosmic time. Finally, we present halo occupation distribution model fits to EAGLE galaxies and show that one flexible six-parameter functional form is capable of fitting a wide range of different mass-and SFR-selected subsamples.