An observational link between AGN Eddington ratio and [NII]λ6583/Ha at 0.6<z<1.7

Abstract

We present an observed relationship between Eddington ratio (λEdd) and optical narrow-emission-line ratio ([N II]λ6583/Hα) of X-ray-selected broad-line active galactic nuclei (AGN) at 0.6 < z < 1.7. We use 27 near-infrared spectra from the Fiber Multi-Object Spectrograph along with 26 sources from the literature. We show that the λEdd and [N II]λ6583/Hα ratio at 0.6 < z < 1.7 exhibits a similar anti-correlation distribution of λEdd-[N II]λ6583/Hα as has been found for local (<z> = 0.036), ultra-hard X-ray selected AGN. The observed distribution implies that there is a consistent relationship from local to z \sim 1.7 which corresponds from the present time to 4 Gyr old. Further study of high redshift low Eddington ratio AGN (logλEdd < -2) is necessary to determine fully whether the λEdd-[N II]λ6583/Hα anti-correlation still holds in high-redshift AGN at low Eddington ratios.

15 pages, 7 figures, and 2 tables; Accepted for publication in ApJ