Detecting faint galaxies by stacking at 24 μm

We stack Spitzer 24 mu m images for similar to 7000 galaxies with 0.1 <= z <= 1 in the Chandra Deep Field South to probe the thermal dust emission in low-luminosity galaxies over this redshift range. Through stacking, we can detect mean 24 mu m fluxes that are more than an order of magnitude below the individual detection limit. We find that the correlations for low- and moderate-luminosity galaxies between the average L-IR/L-UV and rest-frame B-band luminosity, and between the star formation rate (SFR) and L-IR/L-UV, are similar to those in the local universe. This verifies that oft-used assumption in deep UV/optical surveys that the dust obscuration-SFR relation for galaxies with SFR <= 20 M-circle dot yr(-1) varies little with epoch. We have used this relation to derive the cosmic IR luminosity density from z = 1 to z = 0.1. The results also demonstrate directly that little of the bolometric luminosity of the galaxy population arises from the faint end of the luminosity function, indicating a relatively flat faint-end slope of the IR luminosity function with a power-law index of 1.2 +/- 0.3.