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

Abstract

We have developed an efficient Active Galactic Nucleus (AGN) selection method using 18-band Spectral Energy Distribution (SED) fitting in mid-infrared (mid-IR). AGNs are often obscured by gas and dust, and those obscured AGNs tend to be missed in optical, UV and soft X-ray observations. Mid-IR light can help us to recover them in an obscuration free way using their thermal emission. On the other hand, Star-Forming Galaxies (SFG) also have strong PAH emission features in mid-IR. Hence, establishing an accurate method to separate populations of AGN and SFG is important. However, in previous mid-IR surveys, only 3 or 4 filters were available, and thus the selection was limited. We combined AKARI's continuous 9 mid-IR bands with WISE and Spitzer data to create 18 mid-IR bands for AGN selection. Among 4682 galaxies in the AKARI NEP deep field, 1388 are selected to be AGN hosts, which implies an AGN fraction of 29.6$\pm$0.8$\%$ (among them 47$\%$ are Seyfert 1.8 and 2). Comparing the result from SED fitting into WISE and Spitzer colour-colour diagram reveals that Seyferts are often missed by previous studies. Our result has been tested by stacking median magnitude for each sample. Using X-ray data from Chandra, we compared the result of our SED fitting with WISE's colour box selection. We recovered more X-ray detected AGN than previous methods by 20$\%$.

11 pages, 13 figures; accepted for publication in MNRAS; A video summary: https://www.youtube.com/watch?v=gMfH0vkStqk

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• AGN Feedback in SDSS-IV MaNGA: AGNs have Suppressed Central Star Formation Rates
• Search for Optically Dark Infrared Galaxies without Counterparts of Subaru Hyper Suprime-Cam in the AKARI North Ecliptic Pole Wide Survey Field
• Active Galactic Nuclei as seen by the Spitzer Space Telescope
• Extinction-free Census of AGNs in the $AKARI$/IRC North Ecliptic Pole Field from 23-band Infrared Photometry from Space Telescopes
• A Chandra Virgo cluster survey of spiral galaxies. I. Introduction to the survey and a new ULX sample
• CFHT MegaPrime/MegaCam $u$-band source catalogue of the $AKARI$ North Ecliptic Pole Wide field
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• Does AGN Fraction Depend on Redshift or Luminosity? An Extinction-Free Test by 18-band Mid-infrared SED Fitting in the AKARI NEP Wide Field
• Connecting MeerKAT radio continuum properties to GAMA optical emission-line and WISE mid-infrared activity
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• Infrared Colours and Spectral Energy Distributions of Hard X-ray Selected Obscured and Compton-thick AGN
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