The most luminous quasars do not live in the most massive dark matter haloes at any redshift

Quasars (QSOs) represent the brightest active galactic nuclei (AGN) in the Universe and are thought to indicate the location of prodigiously growing black holes (BHs), with luminosities as high as 10⁴⁸ erg s^-1. It is often expected though that such an extremely energetic process takes place in the most massive bound structures in the dark matter (DM) distribution. Weshow that in contrast to this expectation, in a galaxy formation model which includes AGN feedback, QSOs are predicted to live inDMhaloes with typical masses of a fewtimes 10¹²M⊙. Such an environment is considered to be average in the low-redshift universe (z < 2-3) and almost comparable to a Milky Way halo. This fundamental prediction arises from the fact that QSO activity (i.e. BH accretion with luminosity greater than 10⁴⁶ erg s^-1) is inhibited in more massive DM haloes, where AGN feedback operates. The galactic hosts of QSOs in our simulations have typical stellar masses of 10¹⁰-10₁₁M⊙, and represent remnants of massive disc galaxies that have undergone a disc instability or galaxy merger. Interestingly, we find no dependence of QSO activity on environment; thus, the typical QSO halo mass remains constant over two orders of magnitude in luminosity. We further show that the z ~ 6 QSOs do not inhabit the largest DM haloes at that time as these environments are already subject to feedback. Their descendants at z = 0 span a wide range of morphologies and galaxy masses, and their BHs typically grow only by a modest factor between z ~ 6 and the present day. We predict that there should be an enhancement in the abundance of galaxies around QSOs at z ~ 5. However, these enhancements are considerably weaker compared to the overdensities expected at the extreme peaks of the DM distribution. Given that high-z QSO descendants are typically found in rich clusters (~10¹⁴M⊙) and very seldom in the most massive haloes, we conclude that it is very unlikely that QSOs observed at z > 5 trace the progenitors of today'ssuperclusters.