A Tentative Detection of the Cosmic Infrared Background at 3.5 μ[CLC]m[/CLC] from [ITAL]COBE[/ITAL]/DIRBE Observations

Abstract

Foreground emission and scattered light from interplanetary dust (IPD) particles and emission from Galactic stellar sources are the greatest obstacles to determining the cosmic infrared background (CIB) from diffuse sky measurements in the ~1-5 μm range. We use ground-based observational limits on the K-band intensity of the CIB in conjunction with sky maps obtained by the Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer satellite to reexamine the limits on the CIB at 1.25, 3.5, and 4.9 μm. Adopting a CIB intensity of 7.4 nW m−2 sr−1 at 2.2 μm, and using the 2.2 μm DIRBE sky map from which the emission from the IPD cloud has been subtracted, we create a spatial template of the Galactic stellar contribution to the diffuse infrared sky. This template is then used to subtract the contribution of the diffuse Galactic stellar emission from the IPD emission-subtracted DIRBE sky maps at 1.25, 3.5, and 4.9 μm. The DIRBE 100 μm data are used to estimate the small contribution of emission from interstellar dust at 3.5 and 4.9 μm. Our method significantly reduces the errors associated with the subtraction of Galactic starlight, leaving only the IPD emission component as the primary obstacle to the detection of the CIB at these wavelengths. The analysis leads to a tentative detection of the CIB at 3.5 μm with an intensity of νIν={9.9+0.312[ν0ICIB(ν0)-7.4]} ± 2.9 nW m−2 sr−1, where ν0ICIB(ν0) is the CIB intensity at 2.2 μm in units of nW m−2 sr−1. The analysis also yields new upper limits (95% confidence limit) on the CIB at 1.25 and 4.9 μm of 68 and 36 nW m−2 sr−1, respectively. The cosmological implications of these results are discussed in this Letter.