Suzaku and SWIFT-BAT observations of a newly discovered Compton-thick AGN

TL;DR

This study confirms the Compton-thick nature of IRAS 04507+0358 using broad-band X-ray observations, revealing a heavily obscured AGN with intrinsic absorption exceeding 1e24 cm^-2 and providing insights into its luminosity and obscuration properties.

Contribution

First detailed broad-band X-ray spectral analysis of a candidate Compton-thick AGN selected via IR and X-ray flux ratios, confirming its heavily obscured nature.

Findings

IRAS 04507+0358 is confirmed as a Compton-thick AGN.

The source has an intrinsic absorption of approximately 1.3-1.5 x 10^24 cm^-2.

The intrinsic 2-10 keV luminosity is estimated at 5-7 x 10^43 erg s^-1.

Abstract

Obscured AGN are fundamental to understand the history of Super Massive Black Hole growth and their influence on galaxy formation. However, the Compton-thick AGN (NH>1e24 cm^-2) population is basically unconstrained, with less than few dozen confirmed Compton-thick AGN found and studied so far. A way to select heavily obscured AGN is to compare the X-ray emission below 10 keV (which is strongly depressed) with the emission from other bands less affected by the absorption, i.e. the IR band. To this end, we have cross-correlated the 2XMM catalogue with the IRAS Point Source catalogue and, by using the X-ray to infrared flux ratio and X-ray colors, we selected a well defined sample of Compton-thick AGN candidates at z<0.1. The aim of this work is to confirm the nature and to study one of these local Compton-thick AGN candidates, the nearby (z=0.029) Seyfert 2 galaxy IRAS 04507+0358, by constraining the amount of intrinsic absorption (NH) and thus the intrinsic luminosity. To this end we obtained deep (100 ks) Suzaku observations (AO4 call) and performed a joint fit with SWIFT-BAT data. We analyzed XMM-Newton, Suzaku and SWIFT-BAT data and we present here the results of this broad-band (0.4-100 keV) spectral analysis. We found that the broad-band X-ray emission of IRAS 04507+0358 requires a large amount of absorption (larger than 1e24 cm^-2) to be well reproduced, thus confirming the Compton-thick nature of this source. In particular, the most probable scenario is that of a mildly (NH (1.3-1.5)x1e24 cm^-2, L(2-10 keV) (5-7)x1e43 erg s^-1) Compton-thick AGN.