# The Clustering of Undetected High-redshift Black Holes and Their Signatures in Cosmic Backgrounds

## TL;DR

This paper develops a new model to analyze the contribution of high-redshift black holes to cosmic background fluctuations, finding that early black hole growth cannot explain the observed signals, and ruling out alternative galactic foreground explanations.

## Contribution

The paper introduces a novel framework combining semi-analytic black hole growth models with hydrodynamical spectra to assess their impact on cosmic background fluctuations.

## Key findings

- High-redshift black holes at z>6 cannot account for the fluctuations due to excessive early growth.
- Black holes at z~2-3 produce poor fits and overestimate local black hole mass density.
- Galactic warm dust foregrounds are unlikely to cause the observed fluctuations.

## Abstract

There exist hitherto unexplained fluctuations in the Cosmic Infrared Background (CIB) on arcminute scales and larger. These have been shown to cross-correlate with the Cosmic X-ray Background (CXB), leading several authors to attribute the excess to a high-redshift growing black hole population. In order to investigate potential sources that could explain this excess, in this paper, we develop a new framework to compute the power spectrum of undetected sources that do not have constant flux as a function of halo mass. In this formulation, we combine a semi-analytic model for black hole growth and their simulated spectra from hydrodynamical simulations. Revisiting the possible contribution of a high-redshift black hole population, we find that too much black hole growth is required at early epochs for z>6 accretion to explain these fluctuations. Examining a population of accreting black holes at more moderate redshifts, z\sim 2-3, we find that such models produce a poor fit to the observed fluctuations while simultaneously overproducing the local black hole mass density. Additionally, we rule out the hypothesis of a missing Galactic foreground of warm dust that produces coherent fluctuations in the X-ray via reflection of Galactic X-ray binary emission. Although we firmly rule out accreting massive black holes as the source of these missing fluctuations, additional studies will be required to determine their origin.