Spitzer Mid‐ to Far‐Infrared Flux Densities of Distant Galaxies
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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 S 24 = 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 S 24 > 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 S 24 > 250 μJy 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 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 < 6 × 10 12 L ⊙ , which, if attributed to star formation, corresponds to ψ < 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.
author list (cited authors)
Papovich, C., Rudnick, G., Le Floc’h, E., van Dokkum, P. G., Rieke, G. H., Taylor, E. N., ... Franx, M.