The Spatial Distribution of the Far-Infrared Emission in NGC 253

We study the far-infrared emission properties of the nearby starburst galaxy NGC 253 based on IRAS maps and an ISOPHOT map at 180 μm. Based on the analysis of the light profiles, we have been able to identify three main structural components: an unresolved nuclear component, an exponential disk, and a kiloparsec-scale bar. In addition, we also found a ring structure at the end of the bar that is particularly conspicuous at 12 μm. The spectral energy distribution of each morphological component has been modeled as thermal dust emission at different temperatures. The unresolved nuclear component is dominated by cold dust emission (T ≃ 50 K), whereas the disk emission is dominated by very cold dust (T ≃ 16 K) plus a contribution from cold dust (T ≃ 55 K). The bar emission corresponds mainly to cold dust (T ≃ 23 K) plus a warm component (T ≃ 148 K). We detect an extension of the disk emission due to very cold dust, which contributes a large fraction (94%) of the total dust mass of the galaxy. The estimated total dust mass is 8.2 × 107 M☉.