2014MNRAS.444.2442V

We investigate the evolutionary properties of a sample of quasars (QSOs) at 5 < z < 6.4 using the semi-analytical hierarchical model GAMETE/QSOdust. We find that the observed properties of these QSOs are well reproduced by a common formation scenario in which stars form according to a standard initial mass function, via quiescent star formation and efficient merger-driven bursts, while the central black hole (BH) grows via gas accretion and BH-BH mergers. Eventually, a strong active galactic nuclei-driven wind starts to clear up the interstellar medium of dust and gas, damping the star formation and un-obscuring the line of sight towards the QSO. In this scenario, all the QSOs hosts have final stellar masses in the range (4-6)x10¹¹ M_☉, a factor of 3-30 larger than the upper limits allowed by the observations. We discuss alternative scenarios to alleviate this apparent tension: the most likely explanation resides in the large uncertainties that still affect dynamical mass measurements in these high-z galaxies. In addition, during the transition between the starburst-dominated and the active QSO phase, we predict that ∼ 40 percent of the progenitor galaxies can be classified as Submillimetre Galaxies, although their number rapidly decreases with redshift.