  Local spheroids show a relation between their masses and those of the
super-massive black holes (SMBH) at their centres, indicating a link between
the major phases of spheroid growth and nuclear accretion. These phases may
correspond to high-z submillimetre galaxies (SMGs) and QSOs, separate
populations with surprisingly similar redshift distributions which may both be
phases in the life cycle of individual galaxies, with SMGs evolving into QSOs.
Here we briefly discuss our recent results in Coppin et al. (2008), where we
have tested this connection by weighing the black holes and mapping CO in
submm-detected QSOs, which may be transition objects between the two phases,
and comparing their baryonic, dynamical and Halpha-derived SMBH masses to those
of SMGs at the same epoch. [abridged]
