Interpreting the cosmic infrared background: Constraints on the evolution of the dust-enshrouded star formation rate

The mid-infrared local luminosity function is evolved with redshift to fit the spectrum of the cosmic infrared background (CIRB) at lambda > 5 mum and the galaxy counts from various surveys at mid-infrared, far-infrared, and submillimeter wavelengths. A variety of evolutionary models provide satisfa ctory fits to the CIRB and the number counts. The degeneracy in the range o f models cannot be broken by current observations. However, the different e volutionary models yield approximately the same comoving number density of infrared luminous galaxies as a function of redshift. Since the spectrum of the cosmic background at lambda > 200 mum is quite sensitive to the evolut ion at high redshift, i.e., z > 1, all models that fit the counts require a flattening at z similar to 0.8 to avoid overproducing the CIRB. About 80% of the 140 mum CIRB is produced at 0 < z < 1.5, while only about 30% of the 850 mum background is produced within the same redshift range. The nature of the evolution is then translated into a measure of the dust-enshrouded s tar formation rate (SFR) density as a function of redshift and compared wit h estimates from rest-frame optical/ultraviolet surveys. The dust-enshroude d SFR density appears to peak at z = 0.8 +/- 0.1, much sooner than previous ly thought, with a value of 0.25(-0.1)(+0.12) M. yr(-1) Mpc(-3), and remain s almost constant up to z similar to 2. At least 70% of this star formation takes place in infrared luminous galaxies with L-IR > 10(11) L.. The long- wavelength observations that constrain our evolutionary models do not stron gly trace the evolution at z > 2 and a drop-off in the dust-enshrouded SFR density is consistent with both the CIRB spectrum and the number counts. Ho wever, a comparison with the infrared luminosity function derived from exti nction-corrected rest-frame optical/ultraviolet observations of the Lyman b reak galaxy population at z similar to 3 suggests that the almost flat como ving SFR density seen between redshifts of 0.8 and 2 extends up to a redshi ft of z similar to 4.