Arrival Directions of Cosmic Rays above 32 EeV from Phase One of the Pierre Auger Observatory

Abstract: A promising energy range to look for angular correlation between cosmic rays of extragalactic origin and their sources is at the highest energies, above few tens of EeV ($1:{\rm EeV}\equiv 10^{18}:$eV). Despite the flux of these particles being extremely low, the area of ${\sim}:3{,}000 : \text{km}^2$ covered at the Pierre Auger Observatory, and the 17-year data-taking period of the Phase 1 of its operations, have enabled us to measure the arrival directions of more than 2,600 ultra-high energy cosmic rays above $32:\text{EeV}$. We publish this data set, the largest available at such energies from an integrated exposure of $122{,}000 : \text{km}^2:\text{sr}:\text{yr}$, and search it for anisotropies over the $3.4\pi$ steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scale, with ${\sim}:15^\circ$ Gaussian spread or ${\sim}:25^\circ$ top-hat radius, is obtained at the $4:\sigma$ significance level for cosmic-ray energies above ${\sim}:40:\text{EeV}$.