Dust in the SINGS galaxy sample

Dust models have been applied to interpret the IR emission from 65 galaxies in the SINGS galaxy survey, allowing dust masses, PAH fractions, and starlight intensities to be determined. The dust models reproduce the global SEDs without requiring "cold" (T ≃ 12K) dust. The bulk of the IR emission appears to be radiated by dust in the diffuse ISM, with starlight intensities similar to the intensity in the solar neighborhood. A fraction f_PDR of the IR emission is radiated by dust in regions of high starlight intensities (e.g., PDRs), with median f_PDR = 0.08. The dust composition is characterized by qPAH, the fraction of the dust mass contributed by PAHs with <10³ C atoms. Galaxies with metallicities Z/Z⊙ < 0.2 tend to have qPAH ≃ 0.01, but galaxies with Z/Z⊙ > 0.4 have qPAH = 0.02 - 0.05. Over the entire sample, with Z/Z.⊙ ranging from 0.1 to 1, the observations are consistent with a constant fraction of interstellar metals being in dust, with M_dust/M_H ≈ 0.01(Z/Z.⊙).