The 9 and 18 micrometer luminosity functions of various types of galaxies with AKARI: Implication for the dust torus structure of AGN

Abstract

We present the 9 and 18 m 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 m and 255 galaxies at 18 m 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 H or by their emission line ratios of [O III]=H and [N II]=H 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 m luminosity.