Extreme CII emission in type 2 quasars at z~2.5: a signature of kappa-distributed electron energies?

Abstract

We investigate the flux ratio between the 1335 A and 2326 A lines of singly ionized carbon in the extended narrow line regions of type 2 quasars at z~2.5. We find the observed CII 1335 / CII] 2326 flux ratio, which is not sensitive to the C/H abundance ratio, to be often several times higher than predicted by the canonical 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.

6 pages, 1 figure, 3 tables. Accepted for publication in MNRAS

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• The ultraviolet CII lines as a diagnostic of kappa-distributed electrons in planetary nebulae
• Witnessing the transformation of a quasar host galaxy at z=1.6
• Electrostatic waves in astrophysical Druyvesteyn plasmas: I. Langmuir waves