  Submillimeter-emitting galaxies (SMGs) are z~2 bolometrically luminous
systems hosting energetic starburst and AGN activity. SMGs may represent a
rapid growth phase that every massive galaxy undergoes before lying on the
well-established black-hole-spheroid mass relationship in the local Universe.
Here we briefly discuss our recent results from Alexander et al. (2008) where
we estimated the masses of the black holes in SMGs using the black-hole virial
mass estimator, finding M_BH~6x10^7 M_solar for typical SMGs. We show that the
black-hole-spheroid mass ratio for SMGs at z~2 was suggestively below that
found for massive galaxies in the local Universe and more than an order of
magnitude below the black-hole-spheroid mass ratio estimated for z~2 quasars
and radio galaxies. We demonstrate that SMGs and their progeny cannot lie on
the elevated z~2 black-hole-spheroid mass relationship of quasars-radio
galaxies without overproducing the space density of the most massive black
holes (M_BH~10^9 M_solar), unless the galaxy spheroid of SMGs is an order of
magnitude lower than that typically assumed (M_SPH~10^10 M_solar). We also show
that the relative black-hole-spheroid growth rates of typical SMGs appear to be
insufficient to significantly increase the black-hole-spheroid mass ratio,
without requiring long duty cycles (~10^9 years), and argue that a more
AGN-dominated phase (e.g., an optically bright quasar) is required to
significantly move SMGs (and their progeny) up the black-hole-spheroid mass
plane.
