# Looking at cosmic near-infrared background radiation anisotropies

## TL;DR

This paper reviews recent advances in studying near-infrared cosmic background radiation anisotropies, highlighting significant fluctuations linked to early universe sources and black holes, and discusses future prospects with Euclid.

## Contribution

It summarizes recent progress in detecting and analyzing CIB fluctuations, emphasizing their connection to early stars and black holes, and introduces the LIBRAE project for future high-precision measurements.

## Key findings

- Detection of significant source-subtracted CIB fluctuations exceeding known galaxy contributions
- Observed coherence between CIB fluctuations and unresolved cosmic X-ray background
- Potential for upcoming Euclid measurements to transform understanding of early universe sources

## Abstract

The cosmic infrared background (CIB) contains emissions accumulated over the entire history of the Universe, including from objects inaccessible to individual telescopic studies. The near-IR (~1-10 mic) part of the CIB, and its fluctuations, reflects emissions from nucleosynthetic sources and gravitationally accreting black holes (BHs). If known galaxies are removed to sufficient depths the source-subtracted CIB fluctuations at near-IR can reveal sources present in the first-stars-era and possibly new stellar populations at more recent times. This review discusses the recent progress in this newly emerging field which identified, with new data and methodology, significant source-subtracted CIB fluctuations substantially in excess of what can be produced by remaining known galaxies. The CIB fluctuations further appear coherent with unresolved cosmic X-ray background (CXB) indicating a very high fraction of BHs among the new sources producing the CIB fluctuations. These observations have led to intensive theoretical efforts to explain the measurements and their properties. While current experimental configurations have limitations in decisively probing these theories, their potentially remarkable implications will be tested in the upcoming CIB measurements with the ESA's Euclid dark energy mission. We describe the goals and methodologies of LIBRAE (Looking at Infrared Background Radiation with Euclid), a NASA-selected project for CIB science with Euclid, which has the potential for transforming the field into a new area of precision cosmology.