Spitzer Mid- to Far-Infrared Flux Densities of Distant Galaxies**This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion laboratory, California Institute of Technology, under NASA contract 1407.
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We study the infrared (IR) properties of high-redshift galaxies using deep Spitzer 24, 70, and 160 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 m flux densities of 1.5 < z < 2.5 galaxies as a function of 24 m flux density, X-ray activity, and rest-frame near-IR color. Galaxies with 1.5 < z < 2.5 and S 24 = 53-250 Jy have L IR derived from their average 24-160 m flux densities within factors of 2-3 of those inferred from the 24 m flux densities only. However, L IR derived from the average 24-160 m flux densities for galaxies with S 24 > 250 Jy and 1.5 < z < 2.5 are lower than those inferred using only the 24 m flux density by factors of 2-10. Galaxies with S 24 > 250 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 m emission. Based on the average 24-160 m flux densities, nearly all 24 m-selected galaxies at 1.5 < z < 2.5 have L IR < 6 10 12 L , which, if attributed to star formation, corresponds to < 1000 M 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 10 12 L are quite rare, with a surface density 30 10 deg -2 , corresponding to 2 1 10 -6 Mpc -3 over 1.5 < z < 2.5. 2007. The American Astronomical Society. All rights reserved.
