The Infrared Luminosity Function of Galaxies at Redshifts z = 1 and z ~ 2 in the GOODS Fields

We present the rest-frame 8 μm LF at redshifts z=1 and ~2, computed from Spitzer 24 μm-selected galaxies in the GOODS fields over an area of 291 arcmin². Using classification criteria based on X-ray data and IRAC colors, we identify the AGNs in our sample. The rest-frame 8 μm LFs for star-forming galaxies at redshifts z=1 and ~2 have the same shape as at z~0, but with a strong positive luminosity evolution. The number density of star-forming galaxies with log10(νL^8μm_ν)>11 increases by a factor >250 from redshift z~0 to 1 and is basically the same at z=1 and ~2. The resulting rest-frame 8 μm luminosity densities associated with star formation at z=1 and ~2 are more than 4 and 2 times larger than at z~0, respectively. We also compute the total rest-frame 8 μm LF for star-forming galaxies and AGNs at z~2 and show that AGNs dominate its bright end, which is well described by a power law. Using a new calibration based on Spitzer star-forming galaxies at 0<z<0.6 and validated at higher redshifts through stacking analysis, we compute the bolometric IR LF for star-forming galaxies at z=1 and ~2. We find that the respective bolometric IR luminosity densities are (1.2+/-0.2)×10⁹ and (6.6^+1.2_-1.0)×10⁸ L_solar Mpc^-3, in agreement with previous studies within the error bars. At z~2, around 90% of the IR luminosity density associated with star formation is produced by luminous and ultraluminous IR galaxies, with the two populations contributing in roughly similar amounts. Finally, we discuss the consistency of our findings with other existing observational results on galaxy evolution.