The Resolved Distributions of Dust Mass and Temperature in Local Group Galaxies

We utilize archival far-infrared maps from the Herschel Space Observatory in four Local Group galaxies (Small and Large Magellanic Clouds (SMC and LMC), M31, and M33). We model their spectral energy distribution from 100 to 500 itm using a single-temperature modified blackbody emission with a fixed emissivity index of beta = 1.8. From the best-fit model, we derive the dust temperature, T-d, and the dust mass surface density, Sigma(d), at 13 pc resolution for SMC and LMC, and at 167 pc resolution for all targets. This measurement allows us to build the distribution of dust mass and luminosity as functions of dust temperature and mass surface density. We compare those distribution functions among galaxies and between regions in a galaxy. We find that LMC has the highest mass-weighted average T-d, while M31 and M33 have the lowest mass-weighted average T-d. Within a galaxy, star-forming regions have higher T-d and Sigma(d) relative to the overall distribution function, because of more intense heating by young stars and higher gas mass surface density. When we degrade the resolutions to mimic distant galaxies, the mass-weighted mean temperature gets warmer as the resolution gets coarser, meaning that the temperatures derived from unresolved observations are systematically higher than those in highly resolved observations. As an implication, the total dust mass is lower (underestimated) in coarser resolutions. This resolution-dependent effect is more prominent in clumpy star-forming galaxies (SMC, LMC, and M33) and less prominent in a more quiescent massive spiral (M31).