Extreme C II emission in type 2 quasars at z ∼ 2.5: a signature of κ-distributed electron energies?

We investigate the flux ratio between the 1335 angstrom and 2326 angstrom lines of singly ionized carbon in the extended narrow-line regions of type 2 quasars at z similar to 2.5. We find the observed C II lambda 1335/C II] lambda 2326 flux ratio, which is not sensitive to the C/H abundance ratio, to be often several times higher than predicted by the canonical active galactic nucleus (AGN) photoionization models that use solar metallicity and a Maxwell-Boltzmann electron energy distribution. We study several potential solutions for this discrepancy: low gas metallicity, shock ionization, continuum fluorescence, and kappa-distributed electron energies. Although we cannot definitively distinguish between several of the proposed solutions, we argue that a kappa distribution gives the more natural explanation. We also provide a grid of AGN photoionization models using kappa-distributed electron energies.