AKARI Observation of the Sub-degree Scale Fluctuation of the Near-infrared Background

TL;DR

This study analyzes near-infrared sky brightness fluctuations using AKARI data, revealing excess fluctuations at large scales that are consistent across wavelengths and with previous Spitzer observations, but their origin remains uncertain.

Contribution

It extends fluctuation analysis to larger angular scales using AKARI NEP data and confirms the spectral and scale consistency of excess fluctuations with prior observations.

Findings

Residual fluctuations exceed shot noise at large scales.

Excess fluctuation connects smoothly across scales and wavelengths.

Results are consistent with Spitzer observations at 3.6 microns.

Abstract

We report spatial fluctuation analysis of the sky brightness in near-infrared from observations toward the north ecliptic pole (NEP) by the AKARI at 2.4 and 3.2 micron. As a follow up study of our previous work on the Monitor field of AKARI, we used NEP deep survey data, which covered a circular area of about 0.4 square degrees, in order to extend fluctuation analysis at angular scales up to 1000". We found residual fluctuation over the estimated shot noise at larger angles than the angular scale of the Monitor field. The excess fluctuation of the NEP deep field smoothly connects with that of the Monitor field at angular scales with a few hundreds arcseconds and extends without any significant variation to larger angular scales up to 1000". By comparing excess fluctuations at two wavelengths, we confirm a blue spectrum feature similar to the result of the Monitor field. We find that the result of this study is consistent with Spitzer Space Telescope observations at 3.6 micron. The origin of the excess fluctuation in the near-infrared background remains to be answered, but we could exclude zodiacal light, diffuse Galactic light, and unresolved faint galaxies at low-redshift based on the comparison with mid- and far-infrared brightness, ground based near-infrared images.