# Characteristics of mid-infrared PAH emission from star-forming galaxies selected at 250 {\mu}m in the North Ecliptic Pole (NEP) field

## TL;DR

This study investigates the mid-infrared PAH emission characteristics of star-forming galaxies at z<1 selected from 250 μm data, revealing PAH deficits in luminous IR galaxies and supporting a downsizing evolutionary pattern.

## Contribution

It provides a comprehensive analysis of PAH features in IR-luminous galaxies using continuous IR coverage and accurate redshifts, highlighting PAH deficits in more luminous galaxies and their evolutionary implications.

## Key findings

- PAH features are present in most z<1 IR galaxies, mainly normal star-forming types.
- PAH deficit correlates with higher IR luminosity, indicating possible PAH destruction.
- Mass-dependent specific SFR suggests downsizing in galaxy evolution.

## Abstract

Evolutionary properties of infrared (IR) luminous galaxies are important keys to understand dust-obscured star formation history and galaxy evolution. Based on the near- to mid-IR imaging with 9 continuous filters of AKARI space telescope, we present the characteristics of dusty star-forming (SF) galalxies 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 {\mu}m detection and optical spectroscopic redshift data. The physical modelling of spectral energy distribution (SED) using all available data points from u to sub-mm 500 {\mu}m band, including WISE and PACS data where available, takes unique advantages of the continuous near to mid-IR coverage, reliable constraint on far-IR peak, spectroscopically determined accurate redshifts, as well as energy balance principle by MAGPHYS. This enables us to derive physically meaningful and accurate total infrared luminosity and 8 {\mu}m (or PAH) luminosity consistently. Our sample galaxies are in the redshift range z <1, and majority of them appear to be normal SF/spiral populations showing PAH features near the 8 {\mu}m. These SF galaxies showing PAHs in the mid-IR include various types from quiescent to starbursts. Some of our sample show shortage of 8 {\mu}m luminosity compared to the total IR luminosity and this PAH deficit gets severe in more luminous IR galaxies, suggesting PAH molecules in these galaxies destroyed by strong radiation field from SF region or a large amount of cold dust in ISM. The specific SFR of our sample shows mass dependent time evolution which is consistent with downsizing evolutionary pattern.