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Keywords:

  • cosmic rays;
  • galaxies: active

ABSTRACT

We investigate several aspects of the correlations reported by the Pierre Auger Observatory between the highest energy ultra-high energy cosmic rays (UHECRs) and galaxies in the Veron-Cetty Veron (VCV) catalogue of active galactic nuclei (AGNs). First, we quantify the extent of the inhomogeneity and impurity of the VCV catalogue. Second, we determine how the correlation between the highest energy Auger UHECRs and VCV galaxies is modified when only AGNs satisfying optical spectral line ratios, i.e. a very pure sample, are used. Finally, we measure the correlation between the published Auger UHECRs and the distribution of nearby galaxies. We find that the correlation between the arrival directions of published Auger UHECRs and the VCV AGNs is much stronger than the correlation with the random sets of galaxies drawn from nearby large-scale structure. This suggests that the correlation of the UHECRs with AGNs is not solely due to AGNs tracing the large-scale distribution of matter. We also find that once we take into account the heavy oversampling of the VCV catalogue in the Virgo region, the lack of UHECRs from that region is not incompatible with UHECRs having AGN sources.