The spin-orbit-split L-gap surface states on Au(111) are investigated by means of spin- and angle-resolved photoelectron spectroscopy and relativistic first-principles calculations, the latter including both electronic structure and photoemission. The dispersion, momentum distribution and spin polarization of the surface states are consistent with those of a two-dimensional electron gas with Rashba-Bychkov spin-orbit coupling (SOC). The surface symmetry manifests itself in the spin-integrated photoemission intensities, thereby providing details of the orbital composition of the surface states. For the spin polarization, modulations which show up in theory are below the experimental detection limit of 5%. The dependence of both dispersion and spin polarization on the SOC strength are addressed theoretically. The combination of experiment and theory establishes a consistent picture of the L-gap surface states.