The European Large Area ISO Survey -- VI. Discovery of a new hyperluminous infrared galaxy

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90 μm, and is found to be a broad-line, radio-quiet quasar at a redshift z = 1.099. From a detailed multicomponent model fit of the spectral energy distribution, we derive a total IR luminosity LIR (1-1000 μm) ≈ 1.0 × 1013 h-265 L⊙ (0 = 0.5), and discuss the possible existence of a starburst contributing to the far-IR output. Observations to date present no evidence for lens magnification. This galaxy is one of the very few HyLIGs with a X-ray detection. On the basis of its soft X-ray properties, we suggest that this broad-line object may be the face-on analogue of narrow-line, Seyfert-like HyLIGs.