We present here photometric redshift confirmation of the presence of large scale structure around the z = 1.82 QSO RX J0941 , which shows an overdensity of submm sources .
Radio imaging confirms the presence of the submm sources and pinpoints their likely optical-NIR counterparts .
Four of the five submm sources present in this field ( including the QSO ) have counterparts with redshifts compatible with z = 1.82 .
We show that our photometric redshifts are robust against the use of different spectral templates .
We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K -band luminosity obtaining \log ( M _ { * } / M _ { \odot } ) \sim 11.5 \pm 0.2 , slightly larger than the Schechter mass of present day galaxies , and hence indicating that most of the stellar mass is already formed .
We present optical-to-radio spectral energy distributions ( SEDs ) of the five SCUBA sources .
The emission of RX J0941 is dominated by reprocessed AGN emission in the observed MIR range , while the starburst contribution completely dominates in the submm range .
The SEDs of the other three counterparts are compatible with a dominant starburst contribution above \sim 24 \mu m , with star formation rates SFR \sim 2000 M _ { \odot } /yr , central dust masses \log ( M _ { \mathrm { dust } } / M _ { \odot } ) \sim 9 \pm 0.5 and hence central gas masses \log ( M _ { \mathrm { gas } } / M _ { \odot } ) \sim 10.7 .
There is very little room for an AGN contribution .
From X-ray upper limits and the observed 24 \mu m flux , we derive a maximum 2-10keV X-ray luminosity of 10 ^ { 44 } erg/s for any putative AGN , even if they are heavily obscured .
This in turn points to relatively small black holes with \log ( M _ { \bullet } / M _ { \odot } ) \la 8 and hence stellar-to-black hole mass ratios about one order of magnitude higher than those observed in the present Universe : most of their central black hole masses are still to be accreted .
Local stellar-to-black hole masses ratios can be reached if \sim 1.3 % of the available nuclear gas mass is accreted .