The Cobe Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: Iv. Cosmological Implications

A direct measurement of the extragalactic background light (EBL) can provide important constraints on the integrated cosmological history of star formation, metal and dust production, and the conversion of starlight into infrared emission by dust. In this paper we examine the cosmological implications of the recent detection of the EBL in the 125 to 5000 μm wavelength region by the Diffuse Infrared Background Experiment (DIRBE) and Far Infrared Absolute Spectrophotometer (FIRAS) on board the Cosmic Background Explorer (COBE). We first show that the 140 and 240 μm isotropic residual emission found in the DIRBE data cannot be produced by foreground emission sources in the solar system or the Galaxy. The DIRBE 140 and 240 μm isotropic residuals, and by inference the FIRAS residuals as well, are therefore extragalactic. Assuming that most of the 140 and 240 μm emission is from dust yields a 2σ lower limit of ν I(ν) ≈ 5 nW m−2 sr−1 for the EBL at 100 μm. The integrated EBL detected by the COBE between 140 and 5000 μm is ∼ 16 nW m−2 sr−1, roughly 20−50% of the integrated EBL intensity expected from energy release by nucleosynthesis throughout cosmic history. This also implies that at least ∼ 5−15% of the baryonic mass density implied by Big Bang nucleosynthesis has been cycled through stars. The COBE observations provide important constraints on the cosmic star formation rate, and we calculate the EBL spectrum for various Laboratory for Astronomy and Solar Physics, Code 685, NASA/Goddard Space Flight Center, Greenbelt, MD 20771. [email protected] 2 Raytheon STX, Code 685, NASA/GSFC, Greenbelt, MD 20771 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 Laboratory for Astronomy and Solar Physics, Code 681, NASA/Goddard Space Flight Center, Greenbelt, MD 20771. UCLA, Astronomy Department, Los Angeles, CA 90024-1562