Primordial Black Holes as Coma Cluster Dark Matter and the Unresolved {\gamma}-Ray Background

TL;DR

This paper explores whether primordial black holes could account for some of the gamma-ray background and examines the potential of cross-correlating gamma-ray data with weak lensing to detect their signatures, while also discussing implications for large-scale structure.

Contribution

It proposes a model linking primordial black holes to gamma-ray emission in the Coma cluster and assesses the feasibility of detecting PBH signatures through cross-correlation with weak lensing data.

Findings

PBHs could explain some gamma-ray emission in the Coma cluster.

Current cross-correlation data is consistent with astrophysical sources, not PBHs.

Detecting PBH contributions would require unrealistically high PBH abundances.

Abstract

If 0.1% of the dark matter in the Coma cluster is constituted by primordial black holes (PBHs) with masses ranging from 10^-19 to 10^-17 solar masses, then the observed GeV {\gamma}-ray emission from the cluster could potentially be attributed to Hawking radiation. The emitted spectrum is inversely proportional to the black hole's mass, meaning lighter PBHs radiate at higher energies, potentially falling within the GeV range. If 0.1% of the Coma cluster's dark matter is PBH in this mass range, a fit to the cluster's GeV emission is obtained. We then investigate the potential for constraining evaporating PBHs through cross-correlations between the Unresolved Gamma-Ray Background and weak gravitational lensing. Utilizing 12 years of Fermi-LAT observations and weak lensing measurements from the Dark Energy Survey Year 3, we assess whether such correlations can reveal a PBH {\gamma}-ray component. While a statistically significant correlation between the UGRB and large-scale structure has been observed, this signal is consistent with emission from clustered astrophysical sources such as blazars. Attributing a measurable fraction of the UGRB to PBH evaporation would require unrealistically large PBH abundances. We also draw attention to a cluster of Coma-like X-ray clusters, designated Draco X, observed at a redshift of z = 0.12. These systems, characterized by their significant X-ray emission from hot, diffuse intracluster gas, represent massive gravitationally bound structures. The existence and properties of such clusters at these redshifts provide crucial cosmological probes, offering insights into the formation and evolution of large-scale structure and the underlying cosmological parameters. Further investigation of Draco X and similar high-redshift clusters would yield additional constraints on large scale structure.