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 H \alpha -derived SMBH masses to those of SMGs at the same epoch .
Our results split our sample of submm-detected QSOs into two categories ( although a bigger sample would probably show a continuous trend ) : ( 1 ) CO is detected in 5/6 very optically luminous ( M _ { \mathrm { B } } \sim - 28 ) submm-detected QSOs with BH masses M _ { \mathrm { BH } } \simeq 10 ^ { 9 } –10 ^ { 10 } M _ { \odot } , confirming the presence of large gas reservoirs of M _ { \mathrm { gas } } \simeq 3.4 \times 10 ^ { 10 } M _ { \odot } .
Our BH masses and dynamical mass constraints on the host spheroids suggest , at face value , that these optically luminous QSOs at z = 2 lie about an order of magnitude above the local BH-spheroid relation , M _ { \mathrm { BH } } / M _ { \mathrm { sph } } .
However , we find that their BH masses are \sim 30 times too large and their surface density is \sim 300 times too small to be related to typical SMGs in an evolutionary sequence .
( 2 ) We measure weaker CO emission in four fainter ( M _ { \mathrm { B } } \sim - 25 ) submm-detected QSOs with properties , BH masses ( M _ { \mathrm { BH } } \simeq 5 \times 10 ^ { 8 } M _ { \odot } ) , and surface densities similar to SMGs .
These QSOs appear to lie near the local M _ { \mathrm { BH } } / M _ { \mathrm { sph } } relation , making them plausible ‘ transition objects ’ in the proposed evolutionary sequence linking QSOs to the formation of massive young galaxies and BHs at high- z .