AGN selection by 18-band SED fitting in mid-infrared in the AKARI NEP deep field

TL;DR

This paper introduces a new 18-band SED fitting method in the mid-infrared to improve AGN selection in the AKARI NEP deep field, significantly increasing detection efficiency over traditional color-color diagram techniques.

Contribution

The study presents a novel SED fitting approach using 18 IR bands, enhancing AGN identification accuracy beyond previous color-based methods.

Findings

SED fitting recovers 50% of X-ray AGNs, doubling previous methods' efficiency.

The method identifies twice as many AGNs in the NEP sample compared to color selection.

Results suggest a potentially stronger black hole accretion history than previously thought.

Abstract

In this research, we provide a new, efficient method to select infrared (IR) active galatic nucleus (AGN). In the past, AGN selection in IR had been established by many studies using color-color diagrams. However, those methods have a problem in common that the number of bands is limited. The AKARI North Ecliptic Pole (NEP) survey was carried out by the AKARI Infrared Camera (IRC), which has 9 filters in mid-IR with a continuous wavelength coverage from 2 to 24$\mu$m$^{-1}$. Based on the intrinsic different mid-IR features of AGN and star-forming galaxies (SFGs), we performed SED fitting to separate these two populations by the best-fitting model. In the X-ray AGN sample, our method by SED fitting selects 50$\%$ AGNs, while the previous method by colour criteria recovers only 30$\%$ of them, which is a significant improvement. Furthermore, in the whole NEP deep sample, SED fitting selects two times more AGNs than the color selection. This may imply that the black hole accretion history could be more stronger than people expected before.