A Tentative Detection of the Cosmic Infrared Background at 3.5 microns from COBE/DIRBE Observations

Abstract

Foreground emission and scattered light from interplanetary dust (IPD) particles and emission from Galactic stellar sources are the greatest obstacles for determining the cosmic infrared background (CIB) from diffuse sky measurements in the ~ 1 to 5 micron range. We use ground-based observational limits on the K-band intensity of the CIB in conjunction with skymaps obtained by the Diffuse Infrared Background Experiment (DIRBE) on the COBE satellite to reexamine the limits on the CIB at 1.25, 3.5, and 4.9 microns. Adopting a CIB intensity of 7.4 nW m-2 sr-1 at 2.2 microns, and using the 2.2 micron DIRBE skymap from which the emission from 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 skymaps. The DIRBE 100 micron data are used to estimate the small contribution of emission from interstellar dust at 3.5 and 4.9 microns. Our method significantly reduces the errors associated with the subtraction of Galactic starlight, leaving only the IPD emission component as the primary obstacle for the detection of the CIB at these wavelengths. This analysis leads to a tentative detection of the CIB at 3.5 microns. The cosmological implications of these results are discussed in the paper.