Spitzer mid- to far-infrared flux densities of distant galaxies

We study the infrared (IR) properties of high-redshift galaxies using deep Spitzer 24, 70, and 160 mu m data. Our primary interest is to improve the constraints on the total IR luminosities, L-IR, of these galaxies. We combine the Spitzer data in the southern Extended Chandra Deep Field with a K-s-band-selected galaxy sample and photometric redshifts from the Multiwavelength Survey by Yale-Chile. We used a stacking analysis to measure the average 70 and 160 mu m flux densities of 1.5 < z < 2.5 galaxies as a function of 24 mu m flux density, X-ray activity, and rest-frame near-IR color. Galaxies with 1.5 < z < 2.5 and S-24 = 53-250 mu Jy have L-IR derived fromtheir average 24-160 mu m flux densities within factors of 2-3 of those inferred from the 24 mu m flux densities only. However, L-IR derived from the average 24-160 mu m flux densities for galaxies with S-24 > 250 mu Jy and 1.5 < z < 2.5 are lower than those inferred using only the 24 mu m flux density by factors of 2-10. Galaxies with S-24 > 250 mu Jy have S-70/S-24 flux ratios comparable to sources with X-ray detections or red rest-frame IR colors, suggesting that warm dust possibly heated by AGNs may contribute to the high 24 mu m emission. Based on the average 24-160 mu m flux densities, nearly all 24 mu m-selected galaxies at 1.5 < z < 2.5 have L-IR < 6 x 10(12) L-circle dot, which, if attributed to star formation, corresponds to Psi < 1000 M-circle dot yr(-1). This suggests that high-redshift galaxies may have star formation efficiencies and feedback processes similar to those of local analogs. Objects with L-IR > 6 x 10(12) L-circle dot are quite rare, with a surface density similar to 30 +/- 10 deg(-2), corresponding to similar to 2 +/- 1 x 10(-6) Mpc(-3) over 1.5 < z < 2.5.