Infrared spectral energy distributions of z ∼ 0.7 star-forming galaxies

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^-1) 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.