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The bulk of observed ultrahigh energy cosmic rays could be light or heavierelements, and originate from an either steady or transient population ofsources. This leaves us with four general categories of sources. Energeticrequirements set a lower limit on single source luminosities, while thedistribution of particle arrival directions in the sky sets a lower limit onthe source number density. The latter constraint depends on the angularsmearing in the skymap due to the magnetic deflections of the charged particlesduring their propagation from the source to the Earth. We contrast these limitswith the luminosity functions from surveys of existing luminous steady objectsin the nearby universe, and strongly constrain one of the four categories ofsource models, namely, steady proton sources. The possibility that cosmic rayswith energy $> 8\times 10^{19}\,$eV are dominantly pure protons coming fromsteady sources is excluded at 95\% confidence level, under the safe assumptionthat protons experience less than $30^\circ$ magnetic deflection on flight.

The Highest-Energy Cosmic Rays Cannot be Dominantly Protons from Steady Sources