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Published January 2017 | Published + Submitted
Journal Article Open

BAT AGN Spectroscopic Survey – III. An observed link between AGN Eddington ratio and narrow-emission-line ratios


We investigate the observed relationship between black hole mass (MBH), bolometric luminosity (Lbol) and Eddington ratio (λEdd) with optical emission-line ratios ([N ii] λ6583/Hα, [S ii] λλ6716, 6731/Hα, [O i] λ6300/Hα, [O iii] λ5007/Hβ, [Ne iii] λ3869/Hβ and He ii λ4686/Hβ) of hard X-ray-selected active galactic nuclei (AGN) from the BAT AGN Spectroscopic Survey. We show that the [N ii] λ6583/Hα ratio exhibits a significant correlation with λEdd (RPear = −0.44, p-value = 3 × 10−13, σ = 0.28 dex), and the correlation is not solely driven by MBH or Lbol. The observed correlation between [N ii] λ6583/Hα ratio and MBH is stronger than the correlation with Lbol, but both are weaker than the λEdd correlation. This implies that the large-scale narrow lines of AGN host galaxies carry information about the accretion state of the AGN central engine. We propose that [N ii] λ6583/Hα is a useful indicator of Eddington ratio with 0.6 dex of rms scatter, and that it can be used to measure λEdd and thus MBH from the measured Lbol, even for high-redshift obscured AGN. We briefly discuss possible physical mechanisms behind this correlation, such as the mass–metallicity relation, X-ray heating, and radiatively driven outflows.

Additional Information

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Received: 21 June 2016. Revision Received: 24 September 2016. Accepted: 27 September 2016. Published: 28 September 2016. KO and KS acknowledge support from the Swiss National Science Foundation (SNSF) through Project grants 200021_157021, PP00P2_138979, and PP00P2_166159. MK acknowledges support from the SNSF through the Ambizione fellowship grant PZ00P2_154799/1. MK and KS acknowledge support from the SNFS through the Ambizione fellowship grant PP00P2 138979/1. CR acknowledges financial support from the CONICYT-Chile 'EMBIGGEN' Anillo (grant ACT1101), FONDECYT 1141218, Basal-CATA PFB–06/2007 and China-CONICYT fund. ET acknowledges support from the CONICYT-Chile 'EMBIGGEN' Anillo (grant ACT1101), FONDECYT 1160999, and Basal-CATA PFB–06/2007. The work of DS was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This research has made use of NASA's ADS Service. Facilities: Swift, UH:2.2m, Sloan, KPNO:2.1m, FLWO:1.5m (FAST), Shane (Kast Double spectrograph), CTIO:1.5m, Hale, Gemini: South, Gemini: Gillett, Radcliffe, Perkins.

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Published - stw2467.pdf

Submitted - 1609.08625.pdf


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