On the Absence of Broad Forbidden Lines in the Low Luminosity Active Galactic Nucleus; NGC 3227
Abstract
The absence of broad [O III] λλλ4363,4959,5007 forbidden emission lines is the key evidence cited in the published literature for the gas density exceeding the critical density106cm-3, in the broad line region (BLR) of active galactic nuclei (AGN). However, for NGC 3227, an equally valid alternative is that O2+ is completely ionized to become O3+ in the BLR. Evidence in support of this explanation is a conspicuous, broad, permitted C IV λ1549 recombination emission line which implies the existence of photons with energies ≥ 48 eV, and overlapping the ionization potential of O2+. Consequently, according to this interpretation, the absence of broad [O III] forbidden emission lines is due to high ionization rather than high gas density. Thus, the gas density in the BLR of NGC 3227 may be less than 106 cm-3, commensurate, in fact, with a model in which the BLR is essentially a large, steady-state, inflow that is photoionized by the central AGN.
- Publication:
-
American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22312602D