On the origin of the optical and near-infrared extragalactic background light

TL;DR

This paper investigates the excess optical and near-infrared background light, revealing flat fluctuations likely caused by faint compact objects with peculiar spectra, suggesting new astrophysical sources.

Contribution

It proposes faint compact objects as the source of excess background light, supported by fluctuation analysis and spectral characteristics, a novel explanation for the observed phenomena.

Findings

Detected flat fluctuations down to 0.2 arcsec larger than galaxy expectations

FCO surface density estimated at 2.6e3 per square arcsec

FCOs potentially composed of missing baryons with low M/L ratios

Abstract

In optical and near-infrared background light, excess brightness and fluctuation over the known backgrounds have been reported. To delineate their origin, a fluctuation analysis of the deepest optical images was performed, leading to the detection of a flat fluctuation down to 0.2 arcsec, which is much larger than that expected for galaxies. The sky brightness obtained from the detected fluctuation is a few times brighter than the integrated light of the galaxies. These findings require some new objects. As a candidate, faint compact objects (FCOs) whose surface number density rapidly increases to the faint end were proposed. FCOs are very compact and show peculiar spectra with infrared excess. If FCOs cause the excess brightness and fluctuation, the surface number density reaches 2.6e3 in 1 square arcsec. Gamma ray observations require the redshift of FCOs to be less than 0.1 with FCOs consisting of missing baryons. A very low M/L indicates that FCOs are powered by gravitational energy associated with black holes.