Derivation of a large isotropic diffuse sky emission component at 1.25 and 2.2um from the COBE/DIRBE data

Abstract

Using all-sky maps obtained with COBE/DIRBE, we reanalyzed the diffuse sky brightness at 1.25 and 2.2 um, which consists of zodiacal light, diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic emission including the extragalactic background light. Our new analysis including an improved estimate of the DGL and the ISL with the 2MASS data showed that deviations of the isotropic emission from isotropy were less than 10% in the entire sky at high Galactic latitude (|b|>35). The result of our analysis revealed a significantly large isotropic component at 1.25 and 2.2 um with intensities of 60.15 +/- 16.14 and 27.68 +/- 6.21 nWm-2sr-1, respectively. This intensity is larger than the integrated galaxy light, upper limits from gamma-ray observation, and potential contribution from exotic sources (i.e., Population III stars, intrahalo light, direct collapse black holes, and dark stars). We therefore conclude that the excess light may originate from the local universe; the Milky Way and/or the solar system.