Description
Shanks et al (2011, MN, 416, 650) have previously argued that the luminosity and redshift independence of quasar clustering strength implies that all quasars have the same black hole mass. However, this result has been challenged by eg Aird et al (2012, ApJ, 746, 90) who, starting from an inventory of X-ray AGN in complete samples of faint galaxies, suggest that this result simply represents an observational selection effect and that AGN are associated with a wide range of black hole masses. Here we show that the results of Aird et al (2012) are completely compatible with the quasar clustering results and with the view that there is only a small range of black hole mass associated with AGN. Rather than being an observational selection effect, it now seems well established tha all quasars {\bf do} have the same black hole mass and we speculate on the physical origin of this result.
