  The effect of electromagnetic retardation on the spectrum of edge plasmons in
a semi-infinite two-dimensional electron system is considered. The problem is
reduced to complicated integral equations for the potentials, which are solved
upon a major simplification of the kernel. The spatial distribution of the
potentials, charges, and currents is analyzed. It is shown that edge plasmon
polaritons in the high-conductivity two dimensional system are characterized by
a high Q factor at all frequencies, including those lower than the inverse
electron relaxation time.
