Dust emissivity in resolved spiral galaxies

Context. The far-infrared (FIR) and sub-millimeter (submm) emissivity, ϵ ν , of the Milky Way (MW) cirrus is an important benchmark for dust grain models. Dust masses in other galaxies are generally derived from FIR/submm using emission properties these MW-calibrated Aims. We seek to derive nine nearby spiral check its compatibility with MW measurements. Methods. obtained values at 70–500 μm, maps Herschel satellite gas surface density THINGS HERACLES surveys on a scale corresponding 440 pc. studied variation brightness ratio I (250 μm)/ (500 μm), proxy intensity interstellar radiation field heating dust. Results. find that average value agrees estimates pixels sharing same color as cirrus, namely, μm)=4.5. For μm)> 5, measured emissivity instead up factor ∼2 lower than predicted models heated by stronger fields. Regions higher μm) preferentially closer galactic center have overall (stellar+gas) molecular fraction. results do not depend strongly adopted CO-to-molecular conversion appear be affected mixing conditions. Conclusions. Our confirm validity low density, but odds predictions evolution environments. If lower-than-expected high result intrinsic variations properties, it would imply underestimation mass when current