The HELLAS2XMM survey - XII. The infrared/submillimetre view of an X-ray selected type 2 quasar at z ~ 2

We present multiwavelength observations (from optical to submillimetre, including Spitzer and Submillimetre Common-User Bolometer Array) of H2XMMJ003357.2-120038 (also GD158_19), an X-ray selected, luminous narrow-line (type 2) quasar at z = 1.957 selected from the HELLAS2XMM survey. Its broad-band properties can be reasonably well modelled assuming three components: a stellar component to account for the optical and near-infrared (IR) emission; an active galactic nucleus (AGN) component (i.e. dust heated by an accreting active nucleus), dominant in the mid-IR, with an optical depth at 9.7 along the line of sight (close to the equatorial plane of the obscuring matter) of τ(9.7) = 1 and a full covering angle of the reprocessing matter (torus) of 140° and a far-IR starburst component (i.e. dust heated by star formation) to reproduce the wide bump observed longward of 70.

The derived star formation rate is ~1500M_solaryr^-1. The overall modelling indicates that GD158_19 is a high-redshift X-ray luminous, obscured quasar with coeval powerful AGN activity and intense star formation. It is probably caught before the process of expelling the obscuring gas has started, thus quenching the star formation.