Consequences of a Heavy-Metal Scenario of Ultra-High-Energy Cosmic Rays

We assume an extreme scenario, in which the arriving cosmic rays are composed of only iron nuclei at energies above ${10}^{19.6}\text{eV}\simeq 40\text{EeV}$, while allowing a freedom in the scale of the depth of shower maximum ($X_{\mathrm{m}\mathrm{a}\mathrm{x}}$) and preserving the elongation rate and fluctuations of $X_{\mathrm{m}\mathrm{a}\mathrm{x}}$ predicted by models of hadronic interactions. We derive the shift of the $X_{\mathrm{m}\mathrm{a}\mathrm{x}}$ scale for QGSJet II-04 and Sibyll 2.3d models using the public data from the Pierre Auger Observatory. We then propose a new mass-composition model for the energy evolution of four primary species at the ultra-high energies by fitting the publicly-available $X_{\mathrm{m}\mathrm{a}\mathrm{x}}$ distributions. We discuss the consequences of this Heavy-metal scenario on the energy spectrum of individual primary species, hadronic interaction studies, and the effect of the Galactic magnetic field on the arrival directions.