A Compton Thick AGN Powering the Hyperluminous Infrared Galaxy IRAS 00182--7112

TL;DR

This paper reports the discovery of a Compton-thick, ionized reflection-dominated AGN in the hyperluminous infrared galaxy IRAS 00182--7112, revealing its dominant role in powering the galaxy's infrared emission.

Contribution

First identification of a hidden, ionized, Compton-thick AGN dominating the energetics of a hyperluminous infrared galaxy based on X-ray spectral analysis.

Findings

The AGN is Compton-thick and dominated by ionized reflection.

The AGN could dominate the galaxy's FIR emission.

Star formation rate is insufficient to power the FIR, indicating AGN dominance.

Abstract

We present X-ray observations of the Hyperluminous Infrared Galaxy (HLIRG) IRAS 00182--7112 (F00183--7111) obtained using the XMM-Newton EPIC camera. A luminous hard X-ray source co-incident with the nucleus is revealed, along with weaker soft X-ray emission which may be extended or offset from the hard. 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 AGN which is seen only in scattered light. Perhaps the most remarkable characteristic of the spectrum is that the Fe K$\alpha$ 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 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 PAH features both give estimates of the star formation rate $\sim 300 M_{\odot}$ yr$^{-1}$, insufficient to power the FIR emission and supportive of the idea that this HLIRG is AGN-dominated.