Aromatic features in AGNs: Star-forming infrared luminosity function of AGN host galaxies

We describe observations of aromatic features at 7.7 and 11.3 mu m in AGNs of three types, including PG, 2MASS, and 3CR objects. The feature has been demonstrated to originate predominantly from star formation. Based on the aromatic-derived star-forming luminosity, we find that the far-IR emission of AGNs can be dominated by either star formation or nuclear emission; the average contribution from star formation is around 25% at 70 and 160 mu m. The star-forming infrared luminosity functions of the three types of AGNs are flatter than those of field galaxies, implying that nuclear activity and star formation tend to be enhanced together. The star-forming luminosity function is also a function of the strength of nuclear activity from normal galaxies to the bright quasars, with luminosity functions becoming flatter for more intense nuclear activity. Different types of AGNs show different distributions in the level of star formation activity, with 2MASS > PG > 3CR star formation rates.