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We report the results of a Spitzer infrared study of the Cosmic Eye, astrongly lensed, L*_UV Lyman Break Galaxy (LBG) at z=3.074. We obtained SpitzerIRS spectroscopy as well as MIPS 24 and 70 micron photometry. The Eye isdetected with high significance at both 24 and 70 microns and, when including aflux limit at 3.5 mm, we estimate an infrared luminosity of L_IR = 8.3(+4.7-4.4) x10^11 L_sun assuming a magnification of 28+-3. This L_IR is eighttimes lower than that predicted from the rest-frame UV properties assuming aCalzetti reddening law. This has also been observed in other young LBGs, andindicates that the dust reddening law may be steeper in these galaxies. Themid-IR spectrum shows strong PAH emission at 6.2 and 7.7 microns, withequivalent widths near the maximum values observed in star-forming galaxies atany redshift. The L_PAH-to-L_IR ratio lies close to the relation measured inlocal starbursts. Therefore, L_PAH or L_MIR may be used to estimate L_IR andthus, star formation rate, of LBGs, whose fluxes at longer wavelengths aretypically below current confusion limits. We also report the highest redshiftdetection of the 3.3 micron PAH emission feature. The PAH ratio,L_6.2/L_3.3=5.1+- 2.7, and the PAH-to-L_IR ratio, L_3.3/L_IR = 8.5 +- 4.7x10^-4, are both in agreement with measurements in local starbursts and ULIRGs,suggesting that this line may serve as a good proxy for L_PAH or L_IR at z > 3with the James Webb Space Telescope.

Detection of PAH and Far-Infrared Emission from the Cosmic Eye: Probing the Dust and Star Formation of Lyman Break Galaxies