Dark matter accretion wakes of high-redshift black holes

TL;DR

This paper investigates how high-redshift black holes create dark matter accretion wakes due to recoil effects, potentially leading to gamma-ray emission from dark matter annihilation, and estimates their contribution to the gamma-ray background.

Contribution

It introduces a model for dark matter wakes around recoiled black holes at high redshift and evaluates their gamma-ray emission and contribution to the cosmic gamma-ray background.

Findings

High-density dark matter wakes form around recoiled black holes at high redshift.

Gamma-ray emission from dark matter annihilation in these wakes is significant.

The contribution of these wakes to the diffuse gamma-ray background is quantified.

Abstract

Anisotropic emission of gravitational waves during the merger or formation of black holes can lead to the ejection of these black holes from their host galaxies. A recoiled black hole which moves on an almost radial bound orbit outside the virial radius of its central galaxy, in the cold dark matter background, reaches its apapsis in a finite time. The low value of dark matter velocity dispersion at high redshifts and also the black hole velocity near the apapsis passage yield a high-density wake around these black holes. Gamma-ray emission can result from the enhancement of dark matter annihilation in these wakes. The diffuse high-energy gamma-ray background from the ensemble of such black holes in the Hubble volume is also evaluated.