  We present a detailed study of a X -ray selected sample of 5 submillimeter
bright QSOs at $z\sim2$, where the highest rates of star formation (SF) and
further growth of black holes (BH) occur. Therefore, this sample is a great
laboratory to investigate the co-evolution of star formation and AGN. We
present here the analysis of the spectral energy distributions (SED) of the 5
QSOS, including new data from Herschel PACS and SPIRE. Both AGN components
(direct and reprocessed) and like Star Formation (SF) are needed to model its
SED. From the SED and their UV-optical spectra we have estimated the mass of
the black hole ($M_{BH} = 10^9 - 10^{10} M_{SUN}$) and bolometric luminosities
of AGN ($L_{BOL} = (0.8-20) \times 10^{13} L_{SUN}$). These objects show very
high luminosities in the far infrared range (at the H/ULIRG levels) and very
high rates of SF (SFR = 400-1400 $M_{SUN}$/y). Known their current SFR and
their BH masses, we deduce that their host galaxies must be already very
massive, or would not have time to get to the local relation between BH mass
and bulge. Finally, we found evidence of a possible correlation between the
column density of ionized gas detected in X-rays ($NH_{ion}$) and SFR, which
would provide a link between AGN and SF processes.
