Polycyclic aromatic hydrocarbon feature deficit of starburst galaxies in
  the AKARI North Ecliptic Pole Deep Field
  We study the behaviour of polycyclic aromatic hydrocarbon 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 2-24um makes
it possible to measure 8um luminosity, which is dominated by polycyclic
aromatic hydrocarbon emission for galaxies at up to z=2. We compare the IR8 (=
LIR/L(8)) and 8um to 4.5um luminosity ratio (L(8)/L(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 an SED fitting. We found L(8)/L(4.5) increases with starburstiness at log
Rsb < 0.5 and stays constant at higher starburstiness. On the other hand, IR8
is constant at log Rsb < 0, while it 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 polycyclic aromatic hydrocarbon
emission compared with main-sequence galaxies. We also find that galaxies with
extremely high L(8)/L(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.
