  Unexpected in the AGN unified scheme, there exists a population of broad-line
z~2 QSOs which have heavily absorbed X-ray spectra. These objects constitute
10% of the population at luminosities and redshifts characteristic of the main
producers of QSO luminosity in the Universe. Our follow up observations in the
submm show that these QSOs are often embedded in ultraluminous starburst
galaxies, unlike most QSOs at the same redshifts and luminosities. The
radically different star formation properties between the absorbed and
unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus
invoked in AGN unification schemes. Instead, these results suggest that the
objects represent a transitional phase in an evolutionary sequence relating the
growth of massive black holes to the formation of galaxies. The most puzzling
question about these objects has always been the nature of the X-ray absorber.
We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton
spectroscopy. We show that the absorption is most likely due to a dense ionised
wind driven by the QSO. This wind could be the mechanism by which the QSO
terminates the star formation in the host galaxy, and ends the supply of
accretion material, to produce the present day black hole/spheroid mass ratio.
