2014A&A...566A.136M

We study the behaviour of polycyclic aromatic hydrocarbon (PAH) emission in galaxies at z=0.3-1.4 using 1868 samples from the revised catalogue of AKARI North Ecliptic Pole Deep survey. The continuous filter coverage at 2-24µm makes it possible to measure 8µm luminosity, which is dominated by PAH emission, for galaxies at up to z=2. We compare the IR8 (=L_IR/L(8)) and 8µm to 4.5µm luminosity ratio (νL(8)/νL(4.5)) with the starburstiness, R_SB, defined as excess of specific star-formation rate over that of main-sequence galaxy. All AGN candidates were excluded from our sample using a spectral energy distribution fitting. We find νL(8)/νL(4.5) increases with starburstiness at log R_SB<0.5 and stays constant at higher starburstiness. On the other hand, IR8 is constant at log R_SB< 0, while it increases with starburstiness at log R_SB>0. This behaviour is seen in all redshift range of our study. These results indicate that starburst galaxies have deficient PAH emission compared with main-sequence galaxies. We also find that galaxies with extremely high νL(8)/νL(4.5) ratio have only moderate starburstiness. These results suggest that starburst galaxies have compact star-forming regions with intense radiation, which destroys PAHs, and/or have dusty HII regions resulting in a lack of ionising photons.