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Mid and Far Infrared Properties of a Complete Sample of Local Agns

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Mid and Far Infrared Properties of a Complete Sample of Local Agns Draft Version May 24, 2012 A Preprint typeset using LTEX style emulateapj v. 11/26/04 MID AND FAR INFRARED PROPERTIES OF A COMPLETE SAMPLE OF LOCAL AGNS Kohei Ichikawa1, Yoshihiro Ueda1, Yuichi Terashima2, Shinki Oyabu3, Poshak Gandhi4, Keiko Matsuta5, and Takao Nakagawa4 1 Department of Astronomy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake cho, Kyoto, 606-8502, Japan 2 Department of Physics, Faculty of Science, Ehime University, Matsuyama 790-8577, Japan 3 Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 Japan 4 Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan 5 Department of Space and Astronautical Science, The Graduate University for Advanced Studies, 3-1-1Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan Draft Version May 24, 2012 ABSTRACT We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local Active Galactic Nuclei (AGNs) detected in the Swift/BAT all sky hard X-ray (14–195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with IRAS and WISE. Out of 135 non-blazer AGNs in the Swift/BAT 9 month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 µm band. We find good correlation between their hard X-ray and MIR luminosities over 3 orders of magnitude (42 < log λLλ(9, 18 µm) < 45), which is tighter than that with the FIR luminosities at 90 µm. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 µm in the averaged infrared spectral energy distribution from heavy obscured “new type” AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the PAH emission feature, suggesting that their host galaxies have strong starburst activities. Subject headings: galaxies: active — galaxies: nuclei — infrared: galaxies 1. INTRODUCTION (Tueller et al. 2008) is one of the most sensitive all sky A complete survey of Active Galactic Nuclei (AGNs) surveys in the hard X-ray band (>10 keV), providing us throughout the history of the universe is one of main with the least biased sample of AGNs in the local uni- goals in modern astronomy, which is necessary to under- verse including heavily obscured ones, along with those stand the evolution of supermassive black holes (SMBHs) by INTEGRAL (Winkler et al. 2003; Bird et al. 2010). in galactic centers and their host galaxies. Given the fact Suzaku follow-up observations of BAT AGNs have dis- that the majority of AGNs are obscured by dust and gas covered a new type of deeply buried AGNs with a very surrounding the SMBH, observations in hard X-ray and small scattering fraction (Ueda et al. 2007; Eguchi et al. mid-infrared (MIR) bands are proposed to be promis- 2009; Winter et al. 2009a). Assuming that the amount of ing tools for detecting the whole populations of AGNs gas responsible for scattering is not much different from (both radio quiet and loud ones) thanks to their strong other objects, it is suggested that these new type AGNs penetrating power than optical/UV lights and soft X- are obscured in a geometrically thick torus with a small rays. In fact, recent deep multi-wavelengths surveys uti- opening angle. Understanding the nature of this popula- lizing these energy bands are discovering a large num- tion is important to reveal their roles in the cosmological evolution of SMBHs and host galaxies. arXiv:1205.5032v1 [astro-ph.GA] 22 May 2012 ber of obscured AGNs (Brandt & Hasinger 2005). Hard X-ray selection gives the most efficient way to have a The MIR band also provides crucial information on the clean AGN sample with little contamination from host inner region of the AGN tori. It is known that a thermal galaxies. On the other hand, MIR selection sometimes continuum in the MIR band originates from hot circum- achieves even better sensitivities in detecting AGN can- nuclear dust heated by optical/UV/X-ray photons from didates than currently available X-ray data below 10 keV the central engine. Many works suggest that MIR emis- for heavily Compton thick AGNs with column densities sion is a good indicator of AGN activity. Horst et al. 24 −2 (2008); Gandhi et al. (2009) have found a strong corre- of NH > 10 cm , although separation of AGN com- ponents from star forming activities could always be- lation between X-ray (2–10 keV) and MIR (12.3 µm) come an issue (Oyabu et al. 2011). To understand the luminosity from the nucleus of Seyfert galaxies, using efficiency and completeness of these surveys at different the VLT/VISIR data where the AGN can be spatially wavelengths, it is quite important to establish the rela- resolved from the host galaxy in many cases. In this tion between hard X-rays and infrared emission of AGNs paper, we statistically examine the correlation between based on a large sample of nearby, bright AGNs for which the infrared and X-ray luminosities of AGNs by utiliz- detailed studies can be made. ing a large uniform sample in the local universe, and The Swift/Burst Alert Telescope (BAT) survey investigate their infrared properties as a function of ob- scuration type. For this purpose, we use the Swift/BAT Electronic address: [email protected] 9-month catalog (Tueller et al. 2008) as the parent sam- 2 Ichikawa et al. ple, whose multiwavelength properties have been inten- liable1. As for the FIS catalog, we only refer to the 90 sively investigated. Here we focus only on “non-blazar” µm data as a representative FIR flux, which achieve the AGNs. As for the infrared data, we primarily use the all- most significant sensitivity improvement compared with sky survey catalogs obtained with AKARI, Japanese first the previous IRAS mission among the four FIR bands. infrared astronomical satellite launched on 2006 Febru- ary 22 (Murakami et al. 2007), which provide unbiased 2.2.2. IRAS Catalogs galaxy samples selected in the mid- and far-infrared The IRAS mission performed an unbiased all sky sur- (FIR) bands with unprecedented sensitivities as an all vey at the 12, 25, 60 and 100 µm bands. The typical sky survey mission. To complement the infrared data position accuracy at 12 and 25 µm is 7 arcsec and 35 of AGNs whose counterparts are not detected or do not arcsec in the scan and cross scan direction, respectively have reliable flux measurements with AKARI, we also (Beichman et al. 1988). In this paper we use two largest utilize the all sky survey catalog of NASA’s Wide-field In- catalogs, the IRAS Point Source Catalog (IRAS-PSC) frared Survey Explorer (WISE; Wright et al. 2010) mis- and the IRAS Faint Source Catalog (IRAS-FSC). IRAS sion, launched in 2010, as well as the catalogs of the In- achieved 10σ point source sensitivities better than 0.7 Jy frared Astronomical Satellite (IRAS; Neugebauer et al. over the whole sky. The IRAS-FSC contains even fainter 1984), a joint project of the US, UK, and the Nether- sources with fluxes of >0.2 Jy in the 12 and 25 µm bands. lands launched on January 25, 1983. In Section 2, we We use only IRAS sources with FQUAL= 3 (the highest present the sample selection criteria and the results of quality) 2. cross correlation between the Swift/BAT and AKARI catalogs. In Section 3, we discuss our two main results, 2.2.3. WISE All-Sky Catalog the luminosity correlations and infrared average SED for different types. The conclusion and summary are given The WISE mission mapped the sky at the 3.4, 4.6, 12, and 22 µm bands, achieving 5σ point source sensi- in section 4. Throughout the paper, we adopt H0 = 70.0 km s−1 Mpc−1, Ω =0.3, and Ω =0.7. tivity better than 0.08, 0.11, 1, and 6 mJy, respectively, M Λ in unconfused regions on the ecliptic poles (Wright et al. 2. SAMPLE 2010). The WISE all-sky survey utilizes the data taken from 2010 January 7 to August 6 3. The source catalog 2.1. Swift/BAT Hard X-ray Catalog contains positional and photometric information for over The Swift/BAT 9-month catalog (Tueller et al. 2008) 563 million objects. The position accuracy estimated contains 137 non-blazar AGNs with a flux limit of 2 × from the comparison with the 2MASS catalog is ∼2 arc- 10−11 erg cm−2 s−1 in the 14–195 keV band. The red- sec at3σ level. In this paper, we only use sources with the shift range of this sample is 0 <z< 0.156. Winter et al. flux quality indicator ph qual = A, which has Signal-to- (2009a) investigated the soft X-ray (0.5–10 keV) prop- Noise ratio larger than 10. Since the angular resolutions erties of 128 (94.8%) BAT-detected non-blazar AGNs of of WISE (6.5 and 12.0 arcsec at 12 and 22 µm, respec- Tueller et al. (2008). By fitting the X-ray spectra taken tively) are slightly worse than those of AKARI IRC (5.5 with Swift/X-Ray Telescope (XRT) or XMM-Newton, and 5.7 arcsec at 9 and 18 µm, respectively), we refer to they derive key spectral parameters, such as the absorp- the profile-fitting photometry of WISE derived by assum- tion column density (NH), covering fraction of the ab- ing point-like sources, for consistency with the AKARI sorber (fc) or the scattering fraction (fs) with respect catalog.
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