Large angular scale fluctuations of near-infrared extragalactic background light based on the IRTS observations

Abstract

We measure the spatial fluctuations of the Near-Infrared Extragalactic Background Light (NIREBL) from 2° to 20° in angular scale at the 1.6 and |$2.2\, \mu \mathrm{m}$| using data obtained with Near-Infrared Spectrometer (NIRS) on board the Infrared Telescope in Space (IRTS). The brightness of the NIREBL is estimated by subtracting foreground components such as zodiacal light, diffuse Galactic light, and integrated star light from the observed sky. The foreground components are estimated using well-established models and archive data. The NIREBL fluctuations for the 1.6 and |$2.2\, \mu \mathrm{m}$| connect well toward the sub-degree scale measurements from previous studies. Overall, the fluctuations show a wide bump with a center at around 1° and the power decreases toward larger angular scales with nearly a single power-law spectrum (i.e., |${F[\sqrt{l(l+1)C_l/2\pi }]} \sim \theta ^{-1}]$|⁠, indicating that the large-scale power is dominated by the random spatial distribution of the sources. After examining several known sources, contributors such as normal galaxies, high-redshift objects, intra-halo light, and far-IR cosmic background, we conclude that the excess fluctuation at around the 1° scale cannot be explained by any of them.