Exploring structure around submm-bright QSO

Abstract

We have assembled a sample of X-ray and submm luminous QSOs which are therefore both growing their central black holes through accretion and forming stars copiously (Stevens+05). They are also surrounded by submm source overdensities (Stevens+10), placing them in the centres of high density peaks of the z~2 Universe, probably giving rise to massive ellipticals like those seen in the local Universe. We explore in detail here the field around one of those QSO: RX J0941 (z=1.82). Radio observations confirm the submm source detections and pinpoint the optical/NIR/MIR counterparts. We have used photometric redshifts and SED matching, showing that at least 4 of the 5 submm sources are associated to the QSO, with very little room for AGN contribution. These are mature galaxies with BH-to-stellar mass ratios about one dex below local values: most of their central BH mass is still to be accreted, which can happen in a few tens of My. The total mass is similar to that of a present-day cD galaxy and local stellar-to-BH masses can be reached if L3% of the available gas mass is accreted.