On the Clustering Bias of Unresolved Gamma-Ray Sources

Abstract

The Unresolved $\gamma$-Ray Background (UGRB) encodes the collective emission of source populations that are too faint to be detected individually, and its cross-correlation with tracers of the large-scale structure has emerged as a powerful tool to characterize those populations. In this work, we analyze the weak-lensing--UGRB cross-correlation using a reference blazar model. By modeling the relation between blazar $\gamma$-ray luminosity and host-halo mass, we infer the average linear bias $⟨b(z)⟩$ and host-halo mass $⟨M(z)⟩$ of the unresolved blazar population. We find that the signal is dominated by moderately biased sources, with $⟨b⟩\gtrsim 2$ at $z\simeq 1$, hosted by halos with $⟨M⟩\sim \mathcal{O}(10^{13}{M}_{\odot })$. Repeating the analysis with a misaligned-AGN model yields consistent bias values, indicating that the result is determined by the clustering properties of the UGRB rather than by the details of the $\gamma$-ray source model.

8 pages, 9 figures