  We explore two generic hypotheses for tracing the sources of ultra-high
energy cosmic rays (UHECRs) in the Universe: star formation rate density or
stellar mass density. For each scenario, we infer a set of constraints for the
emission mechanisms in the accelerators, for their energetics and for the
abundances of elements at escape from their environments. From these
constraints, we generate sky maps above 40~EeV expected from a catalog that
comprises 410,761 galaxies out to 350 Mpc and provides a near-infrared
flux-limited sample to map both stellar mass and star formation rate over the
full sky. Considering a scenario of intermittent sources hosted in every
galaxy, we show that the main features observed in arrival directions of UHECRs
can in turn constrain the burst rate of the sources provided that
magnetic-horizon effects are at play in clusters of galaxies.
