Extinction-free Census of AGNs in the $AKARI$/IRC North Ecliptic Pole Field from 23-band Infrared Photometry from Space Telescopes

TL;DR

This study utilizes AKARI's continuous 9-band infrared coverage and advanced SED modeling to identify obscured AGNs in the NEP-Wide field, revealing their increasing contribution at higher redshifts and demonstrating a method promising for future deep IR surveys.

Contribution

The paper introduces a novel AGN identification method using AKARI's unique IR filter coverage combined with CIGALE SED modeling, improving detection of obscured AGNs.

Findings

Identified 126 AGNs in the NEP-Wide field.

Found that AGN contribution increases with redshift.

Demonstrated effectiveness of mid-IR SED modeling for AGN detection.

Abstract

In order to understand the interaction between the central black hole and the whole galaxy or their co-evolution history along with cosmic time, a complete census of active galactic nuclei (AGN) is crucial. However, AGNs are often missed in optical, UV and soft X-ray observations since they could be obscured by gas and dust. A mid-infrared (mid-IR) survey supported by multiwavelength data is one of the best ways to find obscured AGN activities because it suffers less from extinction. Previous large IR photometric surveys, e.g., $WISE$ and $Spitzer$, have gaps between the mid-IR filters. Therefore, star forming galaxy (SFG)-AGN diagnostics in the mid-IR were limited. The $AKARI$ satellite has a unique continuous 9-band filter coverage in the near to mid-IR wavelengths. In this work, we take advantage of the state-of-the-art spectral energy distribution (SED) modelling software, CIGALE, to find AGNs in mid-IR. We found 126 AGNs in the NEP-Wide field with this method. We also investigate the energy released from the AGN as a fraction of the total IR luminosity of a galaxy. We found that the AGN contribution is larger at higher redshifts for a given IR luminosity. With the upcoming deep IR surveys, e.g., $JWST$, we expect to find more AGNs with our method.