Characteristics of mid-infrared PAH emission from star-forming galaxies selected at 250?μm in the North Ecliptic Pole field

摘要

Evolutionary properties of infrared (IR) luminous galaxies are important keys to understand dust-obscured star formation history and galaxy evolution. Based on near- to mid-IR imaging with nine continuous filters of the AKARI space telescope, we present the characteristics of dusty star-forming (SF) galaxies showing polycyclic aromatic hydrocarbon (PAH) features observed by the North Ecliptic Pole (NEP) wide field survey of AKARI and Herschel. All the sample galaxies from the AKARI/NEP-Wide data are selected based both on the Herschel/SPIRE 250?μm detection and optical spectroscopic redshift data. The physical modeling of spectral energy distribution (SED) using all available data points from u* to sub-mm 500?μm band, including WISE and PACS data where available, takes unique advantages of the continuous near- to mid-IR coverage, the reliable constraint on the far-IR peak, and spectroscopically determined accurate redshifts, as well as the energy balance principle by MAGPHYS. This enables us to derive physically meaningful and accurate total infrared luminosity and 8?μm (or PAH) luminosity consistently. Our sample galaxies are in the redshift range |$z$| 1, and the majority of them appear to be normal SF/spiral populations showing PAH features near 8?μm. These SF galaxies showing PAHs in the mid-IR include various types, from quiescent to starbursts. Some of our sample show shortage of 8?μm luminosity compared to the total IR luminosity and this PAH deficit gets severe in more-luminous IR galaxies, suggesting PAH molecules in these galaxies are destroyed by a strong radiation field from the SF region or a large amount of cold dust in the interstellar medium. The specific SFR of our sample shows mass-dependent time evolution which is consistent with a downsizing evolutionary pattern.