A Compton-thick active galactic nucleus powering the hyperluminous infrared galaxy IRAS 00182-7112

We present X-ray observations of the hyperluminous infrared galaxy (HLIRG) IRAS 001827-112 obtained using the XMM-Newton EPIC camera. A luminous hard X-ray source coincident with the nucleus is revealed, along with weaker soft X-ray emission which may be extended or offset from the hard emission. The EPIC spectrum is extremely flat and shows Fe K alpha emission with very high equivalent width: both are typical characteristics of a buried, Compton-thick active galactic nucleus (AGN) which is seen only in scattered light. Perhaps the most remarkable characteristic of the spectrum is that the Fe Ka line energy is that of He-like iron, making IRAS 00182-7112 the first hidden AGN known to be dominated by ionized, Compton-thick reflection. Taking an appropriate bolometric correction, we find that this AGN could easily dominate the far-infrared (FIR) energetics. The nuclear reflection spectrum is seen through a relatively cold absorber with column density consistent with recent Spitzer observations. The soft X-ray emission, which may be thermal in nature and associated with star-forming activity, is seen unabsorbed. The soft X-rays and weak polycyclic aromatic hydrocarbon features both give estimates of the star formation rate similar to 300M(circle dot) yr(-1), insufficient to power the FIR emission and supportive of the idea that this HLIRG is AGN-dominated.