Dust-Enshrouded AGN Models for Hyperluminous, High-Redshift Infrared Galaxies

Abstract

We investigate models for the power supply and broadband spectral energy distribution (SED) of hyperluminous IR galaxies, recently discovered at high redshifts, in terms of the emission from an active nucleus embedded in a torus-like dusty structure. We find consistent solutions in terms of a simple torus model extended several hundreds of parsecs, with A_V in the equatorial plane of a few hundred and a typical covering factor of over 50%. Objects as different as the prototypical high-z galaxy IRAS F10214, the z = 0.93 IR object IRAS F15307, IRAS 09104, found in a high-z cooling flow, and the optically selected broad absorption line "Cloverleaf" quasar, are all fitted by the same solution for decreasing values of the polar angle to the line of sight and proper scaling of the luminosities. We suggest that such luminous, high-z IR objects are heavily buried quasars surrounded by large amounts of dust with high covering factors and large optical depths. Comparison with ultraviolet-excess QSOs suggests that they are observed during a transient phase. Forthcoming observations in the far-IR will soon allow probing of this phase and its relationship with the—possibly concomitant—formation of the nuclear black hole and the host galaxy.