The HELLAS2XMM survey - XII. The infrared/submillimetre view of anX-ray selected type 2 quasar at z approximate to 2

Abstract

We present multiwavelength observations (from optical to submillimetre,including Spitzer and Submillimetre Common-User Bolometer Array) ofH2XMMJ003357.2-120038 (also GD158_19), an X-ray selected, luminousnarrow-line (type 2) quasar at z = 1.957 selected from the HELLAS2XMMsurvey. Its broad-band properties can be reasonably well modelledassuming three components: a stellar component to account for theoptical 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 mu m along theline of sight ( close to the equatorial plane of the obscuring matter)of tau(9.7) = 1 and a full covering angle of the reprocessing matter(torus) of 140 degrees and a far-IR starburst component (i.e. dustheated by star formation) to reproduce the wide bump observed longwardof 70 mu m.The derived star formation rate is approximate to 1500M(circle dot)yr(-1). The overall modelling indicates that GD158_19 is ahigh-redshift X-ray luminous, obscured quasar with coeval powerful AGNactivity and intense star formation. It is probably caught before theprocess of expelling the obscuring gas has started, thus quenching thestar formation.