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

Kyuseok Oh, Kevin Schawinski, Michael Koss, Benny Trakhtenbrot, Isabella Lamperti, Claudio Ricci, Richard Mushotzky, Sylvain Veilleux, Simon Berney, D. Michael Crenshaw, Neil Gehrels, Fiona Harrison, Nicola Masetti, Kurt T. Soto, Daniel Stern, Ezequiel Treister, Yoshihiro Ueda

Research output: Contribution to journalArticlepeer-review


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, [OI] λ6300/Hα, [OIII] 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.

Original languageEnglish
Pages (from-to)1466-1473
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - 11 Jan 2017
Externally publishedYes


FundersFunder number
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung166159, 157021


    • Black hole physics
    • Galaxies: active
    • Galaxies: nuclei
    • Quasars: general


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