Multi-wavelength Selected Compton-thick AGNs in Chandra Deep Field-South Survey

TL;DR

This study identifies new Compton-thick AGN candidates in the Chandra Deep Field-South using multi-wavelength data, revealing their properties and emphasizing the effectiveness of combined selection methods in deep X-ray surveys.

Contribution

The paper introduces a multi-wavelength approach to discover previously unidentified Compton-thick AGNs in deep X-ray survey data, enhancing detection efficiency.

Findings

Identified 8 new CT AGN candidates using mid-IR excess method.

Confirmed 7 candidates as CT AGNs through multi-wavelength analysis.

Found CT AGNs have higher Eddington ratios than non-CT AGNs.

Abstract

Even in deep X-ray surveys, Compton-thick active galactic nuclei (CT AGNs, ${\rm N_H} \geqslant 1.5~\times~10^{24}~{\rm cm}^{-2}$) are difficult to be identified due to X-ray flux suppression and their complex spectral shape. However, the study of CT AGNs is vital for understanding the rapid growth of black holes and the origin of cosmic X-ray background. In the local universe, the fraction of CT AGNs accounts for 30% of the whole AGN population. We may expect a higher fraction of CT AGNs in deep X-ray surveys, however, only 10% of AGNs have been identified as CT AGNs in the 7 Ms \textit{Chandra} Deep Field-South (CDFS) survey. In this work, we select 51 AGNs with abundant multi-wavelength data. Using the method of the mid-infrared (mid-IR) excess, we select hitherto unknown 8 CT AGN candidates in our sample. Seven of these candidates can confirm as CT AGN based on the multi-wavelength identification approach, and a new CT AGN (XID 133) is identified through the mid-IR diagnostics. We also discuss the X-ray origin of these eight CT AGNs and the reason why their column densities were underestimated in previous studies. We find that the multi-wavelength approaches of selecting CT AGNs are highly efficient, provided the high quality of observational data. We also find that CT AGNs have a higher Eddington ratio than non-CT AGNs, and that both CT AGNs and non-CT AGNs show similar properties of host galaxies.