A relation of the PAH 3.3 um feature with star-forming activity for
  galaxies with a wide range of infrared luminosity
  For star-forming galaxies, we investigate a global relation between
polycyclic aromatic hydrocarbon (PAH) emission luminosity at 3.3 um, L_PAH3.3,
and infrared (8-1000 um) luminosity, L_IR, to understand how the PAH 3.3 um
feature relates to the star formation activity. With AKARI, we performed
near-infrared (2.5-5 um) spectroscopy of 184 galaxies which have L_IR \sim 10^8
- 10^13 L_sun. We classify the samples into infrared galaxies (IRGs; L_IR <
10^11 L_sun), luminous infrared galaxies (LIRGs; L_IR \sim 10^11 -10^12 L_sun)
and ultra luminous infrared galaxies (ULIRGs; L_IR > 10^12 L_sun). We exclude
sources which are likely contaminated by AGN activity, based on the rest-frame
equivalent width of the PAH emission feature (< 40 nm) and the power-law index
representing the slope of continuum emission (Gamma > 1; F_nu \propto
lambda^Gamma). Of these samples, 13 IRGs, 67 LIRGs and 20 ULIRGs show PAH
emission feature at lambda_rest= 3.3 um in their spectra. We find that the
L_PAH3.3/L_IR ratio considerably decreases toward the luminous end. Utilizing
the mass and temperature of dust grains as well as the BrAlpha emission for the
galaxies, we discuss the cause of the relative decrease in the PAH emission
with L_IR.
