Global Star Formation and Mid-Infrared Emission Features in Galaxies

Abstract

In view of the controversy as to whether the global aromatic features in emission (AFEs) can be used as a robust tracer of the current star formation in normal galaxies, we have constructed a simple two-temperature dust emission model consisting of a cold (diffuse) component of 20K and a warm component associated with star-forming regions. Based on a large sample of star-forming galaxies with available homogeneous IRAS infrared and SCUBA sub-mm fluxes, we show that both these dust components contribute to the global AFE emission. Only for very active star-forming galaxies (e.g., with IRAS f_ν(60 μm)/f_ν(100 μm) > 0.6), does the star-forming component become dominant. We show that our model predictions are consistent with the Spitzer archival data in the case of the nearby galaxy NGC6946.