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

A. Humphrey, L. Binette

Abstract
We investigate the flux ratio between the 1335 Å and 2326 Å lines of singly ionized carbon in the extended narrow-line regions of type 2 quasars at z ∼ 2.5. We find the observed C ii λ1335/C ii] λ2326 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 κ-distributed electron energies. Although we cannot definitively distinguish between several of the proposed solutions, we argue that a κ distribution gives the more natural explanation. We also provide a grid of AGN photoionization models using κ-distributed electron energies.

Keywords
galaxies: active, galaxies: high-redshift, galaxies: ISM, galaxies: nuclei, quasars: emission lines

Monthly Notices of the Royal Astronomical Society
Volume 442, Issue 1, Page 753
2014 July

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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