Correlations between Ultrahigh Energy Cosmic Rays and AGNs

TL;DR

This study analyzes the correlation between ultrahigh energy cosmic rays and active galactic nuclei, revealing that a significant fraction of UHECRs likely originate from AGNs, with implications for understanding cosmic ray sources.

Contribution

It provides a detailed assessment of the correlation strength between UHECRs and AGNs, accounting for catalog biases and large-scale matter distribution effects.

Findings

Correlation between UHECRs and AGNs is too strong to be due to large-scale matter distribution alone.

Heavy sampling bias in the VCV catalog affects the observed UHECR distribution.

Some UHECRs are likely produced by AGNs, not just tracing matter distribution.

Abstract

We investigate several aspects of the correlations reported by the Pierre Auger Observatory between the highest energy cosmic rays (UHECRs) and galaxies in the Veron-Cetty Veron (VCV) catalog of AGNs. First, we quantify the extent of the inhomogeneity and impurity of the VCV catalog. Second, we determine how the correlation between the highest energy Auger UHECRs and VCV galaxies is modified when only optically-identified AGNs are used. Finally, we measure the correlation between the published Auger UHECRs and the distribution of matter. Our most important finding is that the correlation between UHECRs and AGNs is too strong to be explained purely by AGNs tracing the large scale distribution of matter, indicating that (barring the correlation being a statistical fluke) some substantial fraction of UHECRs are produced by AGNs. We also find that once we take into account the heavy oversampling of the VCV catalog in the Virgo region, the lack of UHECR events from that region is not incompatible with UHECR having AGN sources.