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

TL;DR

This study investigates PAH emission in starburst galaxies across redshifts 0.3-1.4, revealing a deficit in PAH features in starburst galaxies likely due to intense radiation destroying PAHs or dusty HII regions.

Contribution

It provides new insights into PAH emission behavior in starburst galaxies and how it varies with starburstiness and redshift, using AKARI survey data.

Findings

PAH emission decreases in starburst galaxies compared to main-sequence galaxies.

IR8 remains constant at low starburstiness but increases at higher starburstiness.

PAH deficit is linked to intense radiation in compact star-forming regions.

Abstract

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.