AKARI observation of the fluctuation of the near-infrared background

TL;DR

This study uses AKARI infrared data to detect large-scale sky brightness fluctuations that may originate from the universe's first stars, providing new insights into early cosmic history.

Contribution

First detection of large-scale near-infrared background fluctuations consistent with Pop III star emissions using AKARI satellite data.

Findings

Significant excess fluctuations at scales >10,000 arcsec

Fluctuations have a blue stellar spectrum similar to excess isotropic emission

Spatial correlation across wavelengths supports a primordial origin

Abstract

We report a search for fluctuations of the sky brightness toward the north ecliptic pole (NEP) with the Japanese infrared astronomical satellite AKARI,at 2.4, 3.2, and 4.1 \mum. We obtained circular maps with 100 diameter field of view which clearly show a spatial structure on scale of a few hundred arcsec. A power spectrum analysis shows that there is a significant excess fluctuation at angular scales larger than 10000 that can't be explained by zodiacal light, diffuse Galactic light, shot noise of faint galaxies or clustering of low redshift galaxies. These results are consistent with observations at 3.6 and 4.5 \mum by NASA's Spitzer Space Telescope. The fluctuating component observed at large angular scales has a blue stellar spectrum which is similar to that of the spectrum of the excess isotropic emission observed with IRTS. A significant spatial correlation between wavelength bands was found, and the slopes of the linear correlations is consistent with the spectrum of the excess fluctuation. These findings indicate that the detected fluctuation could be attributed to the first stars of the universe, i.e. pop. III stars. The observed fluctuation provides an important constraints on the era of the first stars.