Two conditions for galaxy quenching: compact centres and massive haloes

We investigate the roles of two classes of quenching mechanisms for central and satellite galaxies in the Sloan Digital Sky Survey (z1011.8 M⊙ are dense (Σ1 kpc>109 M⊙ kpc−2), suggesting compaction-related quenching maintained by halo-related quenching. However, 21 per cent are diffuse, indicating only halo quenching. For satellite galaxies in the outskirts of haloes, quenching is a strong function of compactness and a weak function of host Mh. In the inner halo, Mh dominates quenching, with ∼90 per cent of the satellites being quenched once Mh>1013 M⊙. This regional effect is greatest for the least massive satellites. As demonstrated via semi-analytic modelling with simple prescriptions for quenching, the observed correlations can be explained if quenching due to central compactness is rapid while quenching due to halo mass is slow