2007ApJ...668...45P

We study the infrared (IR) properties of high-redshift galaxies using deep Spitzer 24, 70, and 160 µm 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 µm flux densities of 1.5<z<2.5 galaxies as a function of 24 µm flux density, X-ray activity, and rest-frame near-IR color. Galaxies with 1.5<z<2.5 and S₂₄=53-250 µJy have L_IR derived from their average 24-160 µm flux densities within factors of 2-3 of those inferred from the 24 µm flux densities only. However, L_IR derived from the average 24-160 µm flux densities for galaxies with S₂₄>250 µJy and 1.5<z<2.5 are lower than those inferred using only the 24 µm flux density by factors of 2-10. Galaxies with S₂₄>250 µJy have S₇₀/S₂₄ 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 µm emission. Based on the average 24-160 µm flux densities, nearly all 24 µm-selected galaxies at 1.5<z<2.5 have L_IR<6x10¹² L_☉, which, if attributed to star formation, corresponds to Ψ<1000 M_☉/yr. This suggests that high-redshift galaxies may have star formation efficiencies and feedback processes similar to those of local analogs. Objects with L_IR>6x10¹² L_☉ are quite rare, with a surface density ∼30±10/deg2, corresponding to ∼2±1x10^–6/Mpc3 over 1.5<z<2.5.