Mon. Not. R. Astron. Soc., 426, 2703-2718 (2012/November-2)
Type 1 AGN at low z - II. The relative strength of narrow lines and the nature of intermediate type AGN.
STERN J. and LAOR A.
Abstract (from CDS):
We explore the relative strength of the narrow emission lines in a Sloan Digital Sky Survey based sample of broad Hα selected active galactic nuclei (AGN), defined in Paper I. We find a decrease in the narrow to broad Hα luminosity (L(bHα)) ratio with increasing L(bHα), such that both L([OIII]λ5007) and L(nHα) scale as ∝L(bHα)0.7 for 1040<L(bHα)<1045erg/s. Following our earlier result that L(bHα)∝Lbol, this trend indicates that the relative narrow line luminosity decreases with increasing Lbol. We derive Lbol/1043erg/s = 4000(L([OIII])/1043erg/s)1.39. This implies that the bolometric correction factor, Lbol/L([OIII]), decreases from 3000 at Lbol=1046.1erg/s to 300 at Lbol=1042.5erg/s. At low luminosity, the narrow component dominates the observed Hα profile, and most type 1 AGN appear as intermediate type AGN. Partial obscuration or extinction cannot explain the dominance of intermediate type AGN at low luminosity, and the most likely mechanism is a decrease in the narrow line region covering factor with increasing Lbol. Deviations from the above trend occur in objects with L/LEdd≲10–2.6, probably due to the transition to LINERs with suppressed [OIII] emission, and in objects with MBH>108.5M☉, probably due to the dominance of radio-loud AGN, and associated enhanced [OIII] emission.
© 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS
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