Constraining the astrophysical source populations of Ultra High Energy Cosmic Rays (UHECRs)
is difficult because UHECRs are deflected by the Galactic Magnetic Field (GMF). Recent in-
terpretations of cosmic-ray-produced air showers with LHC-tuned hadronic interaction models
suggest a gradual increase in the mean mass of UHECRs with energy. The decades-old view of
UHECRs being a mix of hydrogen and iron (with relative composition varying with energy) is
now expanding to also consider intermediate nuclear compositions. Notably, while hydrogen and
iron UHECRs have expected mean free paths of ∼ 100Mpc, intermediate composition UHECRs
have mean free paths of only 10s of Mpc.
Monte-Carlo simulations of H, C, N, and O composition UHECR tracks in 8 proposed GMF
models can be used to estimate deflections suffered by the UHECRs detected by the Pierre Auger
Observatory and the Telescope Array. These deflections can be used to identify sub-samples of
’least-deflected’ UHECRs relatively independent of the GMF model assumed. The distribution of
the GMF-deflection-corrected arrival directions of this ’least deflected’ sample can be correlated
with astrophysical catalogs to best constrain whether a substantial population of UHECRs are of
intermediate composition and originate in a specific type of astrophysical source in the very local
universe.
Sotomayor et al. 2022 found a strong association between the (GMF-deflection-corrected) arrival
directions of ’least deflected’ UHECRs with nearby (D ≤ 20 Mpc) galaxies when considering an
oxygen UHECR composition. In this poster we present a continuation of the [1] analysis, but
now using three high-abundance intermediate mass species (C, N, and O), and now weighting
astrophysical samples by the fluxes, luminosities, and other properties (e.g., galaxy mass, star
formation rate, radio and X-ray emission) of their galaxies