Publication Date:
2016-10-27
Description:
We investigate the observed relationship between black hole mass ( M BH ), bolometric luminosity ( L bol ) and Eddington ratio ( Edd ) with optical emission-line ratios ([N ii ] 6583/Hα, [S ii ] 6716, 6731/Hα, [O i ] 6300/Hα, [O iii ] 5007/Hβ, [Ne iii ] 3869/Hβ and He ii 4686/Hβ) of hard X-ray-selected active galactic nuclei (AGN) from the BAT AGN Spectroscopic Survey. We show that the [N ii ] 6583/Hα ratio exhibits a significant correlation with Edd ( R Pear = –0.44, p -value = 3 x 10 –13 , = 0.28 dex), and the correlation is not solely driven by M BH or L bol . The observed correlation between [N ii ] 6583/Hα ratio and M BH is stronger than the correlation with L bol , but both are weaker than the Edd 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 ] 6583/Hα is a useful indicator of Eddington ratio with 0.6 dex of rms scatter, and that it can be used to measure Edd and thus M BH from the measured L bol , 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.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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