Spatial distribution of warm dust in early-type galaxies

Images taken with the Infrared Array Camera on the Spitzer Space Telescope show that the spatial distribution of warm dust emission in lenticular galaxies is often organized into dynamically stable structures strongly resembling spiral arms. These galaxies have bulge-to-disk ratios and colors for their stellar content that are appropriate for their morphological classification. Two of the three galaxies with warm dust detected at 8.0 mum also show far-IR emission expected from that dust. More importantly, the [5.8]-[8.0] color of the dust emission matches the colors found for late-type, star-forming galaxies, as well as theoretical predictions for polycyclic aromatic hydrocarbon emission from dust grains. The spatially resolved dust structures may be powerful indicators of the evolutionary history of the lenticular class of galaxies, either as a tracer of ongoing quiescent star formation or as a fossil record of a previous episode of more active star formation.