Polycyclic aromatic hydrocarbon feature deficit of starburst galaxies in the AKARI North Ecliptic Pole Deep field

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 2–24 μm makes it possible to measure 8 μm luminosity, which is dominated by PAH emission, for galaxies at up to z = 2. We compare the IR8 (≡LIR/L(8)) and 8 μm to 4.5 μm luminosity ratio (νL(8) /νL(4.5)) with the starburstiness, RSB, 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 RSB 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