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For star-forming galaxies, we investigate a global relation betweenpolycyclic 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 umfeature relates to the star formation activity. With AKARI, we performednear-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 excludesources which are likely contaminated by AGN activity, based on the rest-frameequivalent width of the PAH emission feature (< 40 nm) and the power-law indexrepresenting the slope of continuum emission (Gamma > 1; F_nu \proptolambda^Gamma). Of these samples, 13 IRGs, 67 LIRGs and 20 ULIRGs show PAHemission feature at lambda_rest= 3.3 um in their spectra. We find that theL_PAH3.3/L_IR ratio considerably decreases toward the luminous end. Utilizingthe mass and temperature of dust grains as well as the BrAlpha emission for thegalaxies, we discuss the cause of the relative decrease in the PAH emissionwith L_IR.

A relation of the PAH 3.3 um feature with star-forming activity for galaxies with a wide range of infrared luminosity