Does AGN Fraction Depend on Redshift or Luminosity? An Extinction-Free
  Test by 18-band Mid-infrared SED Fitting in the AKARI NEP Wide Field
  Revealing what fraction of galaxies harbor AGN is central in understanding
black hole accretion history of the Universe. However, optical and soft X-ray
surveys miss the most highly obscured AGNs. Infrared (IR), instead, is more
robust against absorption. Previous IR photometric surveys, however, only had 4
or 5 filters in mid-IR. Our AKARI North Ecliptic Pole (NEP) wide field sample
has 18 filters in mid-IR (9 from AKARI, 4 from WISE, and 5 from Spitzer), for
the first time, allowing a sophisticated mid-IR SED fitting diagnosis for a
statistical number of sources (89178 over 5.4 deg$^2$). By using a SED fitting
technique, we investigate the evolution of AGN fraction as a function of
redshift and IR (8-1000 $\mu$m) luminosity in an extinction-free way. We found
that the AGN fraction (F$_{\rm AGN}$) shows no sign of strong redshift
evolution. Instead, F$_{\rm AGN}$ increases with increasing IR luminosity in
all redshifts bins ($0<z<2$).
