Submillimeter-emitting galaxies ( SMGs ) are z \approx 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 } \approx 6 \times 10 ^ { 7 } M _ { \odot } for typical SMGs .
We show that the black-hole–spheroid mass ratio for SMGs at z \approx 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 \approx 2 quasars and radio galaxies .
We demonstrate that SMGs and their progeny can not lie on the elevated z \approx 2 black-hole–spheroid mass relationship of quasars–radio galaxies without overproducing the space density of the most massive black holes ( M _ { BH } \approx 10 ^ { 9 } M _ { \odot } ) , unless the galaxy spheroid of SMGs is an order of magnitude lower than that typically assumed ( M _ { SPH } \approx 10 ^ { 10 } M _ { \odot } ) .
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 .