The importance of super-Eddington black hole accretion for the emergence of massive quiescent galaxies at high redshift

Abstract Recent JWST observations indicate that massive quiescent galaxies (stellar mass M* ≳ 1010 M⊙) at high redshift (z ≳ 6) are more abundant than predicted by most existing galaxy formation simulations and semi-analytic models. Notably, the new colibre simulations have succeeded in reconciling this tension, though the precise reason for their improved agreement with JWST data remains unclear. We demonstrate that the improved agreement is largely due to super-Eddington growth of supermassive black holes (BHs) at high redshift. We run a series of (100 cMpc)3 simulations with the colibre subgrid physics at m7 colibre resolution (gas and dark matter particle masses mgas ≈ mdm ~ 107 M⊙), varying the maximum allowed BH accretion rate in units of the Eddington rate. We show that only the fiducial colibre model, which permits super-Eddington accretion, is consistent with the JWST constraints at z ≳ 6. Moreover, we find that in colibre about 50 per cent of BH mass growth at high redshift occurs in the super-Eddington regime, even though such events are extremely rare in time. Our work highlights the important role of super-Eddington accretion in simulations of galaxy formation for reproducing the observed early emergence of quenching of massive galaxies.