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arXiv · 1708.00201

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

Ting-Chi Huang·Tomotsugu Goto·Tetsuya Hashimoto·Nagisa Oi·Hideo Matsuhara
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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$\%$.

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Ting-Chi Huang, Tomotsugu Goto, Tetsuya Hashimoto, Nagisa Oi, Hideo Matsuhara. 2017-08-01. An extinction free AGN selection by 18-band SED fitting in mid-infrared in the AKARI NEP deep field. https://doi.org/10.1093/mnras/stx1947

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