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

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.

Identification of AKARI infrared sources by the Deep HSC Optical Survey: construction of a new band-merged catalogue in the North Ecliptic Pole Wide field

“…In addition, supplemental observation using the CFHT/MegaPrime (Huang et al 2020) replenished the insufficient coverage of the u * band from the previous CFHT surveys, which brings photoz accuracy improvement along with these new HSC data (Ho et al 2020). The source-matching and band-merging processes (see Section 2 for details) have been encouraging various subsequent works such as the recent luminosity function (LF) update (Goto et al 2019), properties of mid-IR (MIR) galaxies detected at 250 μm (Kim et al 2019), estimation of the number fraction of AGN populations (Chiang et al 2019), a study on high-z populations (Barrufet et al 2020), obscured AGN activity (Wang et al 2020), merger fractions depending on star-formation mode (Kim et al, in preparation), AGN activities depending on the environment (Santos et al, in preparation), machine-learning algorithms to classify/separate IR sources (Poliszczuk et al, in preparation; Chen et al, in preparation), and cluster-candidate finding (Huang et al, in preparation), even on the AKARI sources without any HSC counterpart (Toba et al 2020). The science on the NEP initiated by AKARI is now entering a new era with momentum driven by Subaru/HSC observations as well as current survey projects, such as a homogeneous spectroscopic survey (MMT2020A/B, PI: H. S. Hwang) and 850 μm mapping over the entire NEP area using the Submillimetre Common-User Bolometric Array 2 (SCUBA-2) at the James Clerk Maxwell Telescope (Shim et al 2020).…”

Photometric redshifts in the North Ecliptic Pole Wide field based on a deep optical survey with Hyper Suprime-Cam

“…Note that we are not focusing on AGN classification in this paper, but only separating the stars from this catalogue samples. AGN classification of the NEPW field will be discussed in Wang et al (2020).…”

“…The domination of SFGs in the sample reflects the characteristics of our NIR-and MIR-selected galaxies in the NEP field. Further discussion about galaxy/AGN classification and morphology in NEPW are presented in Wang et al (2020) and Kim et al 2020 (in press), respectively.…”

Environmental effects on AGN activity via extinction-free mid-infrared census

“…Looking at the MIR spectral energy distributions (SEDs) of the sources can therefore help us identify AGNs from SFGs (e.g. Laurent et al 2000;Huang et al 2017;Wang et al 2020;Toba et al 2020a), justifying the utilization of MIR surveys for studying AGNs.…”