The 9 and 18 Micrometer Luminosity Functions of Various Types of Galaxies with AKARI : Implication for the Dust Torus Structure of AGN

The 9 and 18 Micron Luminosity Function of Various Types of Galaxies with AKARI: Implication for the arXiv:1308.2367v1 [astro-ph.CO] 11 Aug 2013 Dust Torus Structure of AGN Yoshiki Toba 1,2 , Shinki Oyabu 3 , Hideo Matsuhara 2 , Matthew A Malkan 4 , Daisuke Ishihara 3 , Takehiko Wada 2 , Youichi Ohyama 5 , Satoshi Takita 2 , and Chisato Yamauchi 6 1 Department of Space and Astronautical Science, the Graduate University for Advanced Studies (Sokendai), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 toba@ir.isas.jaxa.jp 2 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 3 Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 4 Department 5 Institute of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan, R.O.C 6 Astronomy Data Center, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Received 2012 August 22; accepted 2013 July 20) Abstract We present the 9 and 18 µm luminosity functions (LFs) of galaxies at 0.006 ≤ z ≤ 0.8 (with an average redshift of ∼ 0.04) using the AKARI mid-infrared all-sky survey catalog. We selected 243 galaxies at 9 µm and 255 galaxies at 18 µm from the Sloan Digital Sky Survey (SDSS) spectroscopy region. These galaxies were then classified by their optical emission lines, such as the line width of Hα or by their emission line ratios of [OIII]/Hβ and [NII]/Hα into five types: Type 1 active galactic nuclei (AGN) (Type 1); Type 2 AGN (Type 2); low-ionization narrow emission line galaxies (LINER); galaxies with both star formation and narrow-line AGN activity (composite galaxies); and star-forming galaxies (SF). We found that (i) the number density ratio of Type 2 to Type 1 AGNs is 1.73 ± 0.36, which is larger than a result obtained from the optical LF and (ii) this ratio decreases with increasing 18 µm luminosity. Key words: galaxies: active — galaxies: luminosity function, mass function — galaxies: nuclei — infrared: galaxies