Analysis of the Diffuse Near-Infrared Emission from Two-Micron All-Sky Survey Deep Integration Data: Foregrounds versus the Cosmic Infrared Background

This is one of two papers in which we report the detection of structure in the cosmic infrared background (CIB) between 1.25 and 2.2 μm through the use of data from the Two-Micron All-Sky Survey (2MASS). This paper concentrates on data assembly, analysis, and the estimate of the various foreground contributions; the companion Letter presents the cosmological results for the CIB fluctuations and their implications. By using repeated observations of a specific calibration star field, we were able to achieve integration times in excess of 3900 s, compared to the 7.8 s in the standard 2MASS data product. This yielded a point-source detection limit (3 σ) of +18.5 mag in the K_s band. The resulting co-added images were processed to remove point sources to a limiting surface brightness of +20 mag arcsec^-2 or 40 nW m^-2 sr^-1. The remaining maps contained over 90% of the pixels and were Fourier transformed to study the spatial structure of the diffuse background light. After removing resolved sources and other artifacts, we find that the power spectrum of the final images has a power-law distribution consistent with clustering by distant galaxies. We estimate here the contributions to this signal from Galactic foregrounds, atmospheric OH-glow, zodiacal light, and instrument noise, all of which are small and of different slopes. This supports the identification offered in the companion Letter of the signal as coming from the CIB fluctuations produced by distant clustered galaxies.