Detection of Small-Scale Fluctuations in the Near-Infrared Cosmic Infrared Background from Long-Exposure 2MASS Fields

We report first results for the cosmic infrared background (CIB) fluctuations at 1.25, 1.65, and 2.17 μm obtained from long exposures constructed from Two Micron All Sky Survey standard star fields. We have co-added and analyzed scans from one such field with a total exposure time greater than 1 hr and removed sources and other artifacts. The stars and galaxies were clipped out to Ks ≃ 19 mag, leaving only high-z galaxies (or possibly local low surface brightness systems). The angular power spectrum of the remaining diffuse emission on scales from a few arcseconds to a few arcminutes has a power-law slope consistent with emission produced by clustered galaxies. The noise (and residual artifacts) contribution to the signal is small, and the colors of the signal are very different from Galactic stars or airglow. We therefore identify the signal as CIB fluctuations from the faint unresolved galaxies. We show that the present-day galaxies with no evolution would produce a significant deficit in the observed CIB fluctuations. Thus, the dominant contribution to the observed signal must come from high z and may indicate high rates of star formation at those epochs.