2007ApJ...670..301Z

We analyze the infrared (IR) spectral energy distributions (SEDs) for 10 µm<λ_rest<100 µm for ∼600 galaxies at z∼0.7 in the extended Chandra Deep Field South by stacking their Spitzer 24, 70, and 160 µm images. We place interesting constraints on the average IR SED shape in two bins: the brightest 25% of z∼0.7 galaxies detected at 24 µm, and the remaining 75% of individually detected galaxies. Galaxies without individual detections at 24 µm were not well detected at 70 and 160 µm even through stacking. We find that the average IR SEDs of z∼0.7 star-forming galaxies fall within the diversity of z∼0 templates. While dust obscuration L_IR/L_UV seems to be only a function of star formation rate (SFR; ∼L_IR+L_UV), not of redshift, the dust temperature of star-forming galaxies (with SFR∼10 M_☉/yr) at a given IR luminosity was lower at z∼0.7 than today. We suggest an interpretation of this phenomenology in terms of dust geometry: intensely star-forming galaxies at z∼0 are typically interacting, and host dense centrally concentrated bursts of star formation and warm dust temperatures. At z∼0.7, the bulk of intensely star-forming galaxies are relatively undisturbed spirals and irregulars, and we postulate that they have large amounts of widespread lower density star formation, yielding lower dust temperatures for a given IR luminosity. We recommend which IR SEDs are most suitable for modeling intermediate-redshift galaxies with different SFRs.