We present the optical narrow line ratios in an SDSS based sample of 3 175 broad H \alpha selected type 1 AGN , and explore their positions in the BPT diagrams as a function of the AGN and the host properties .
We find the following : 1 .
The luminosities of all measured narrow lines ( H \alpha , H \beta , [ O iii ] , [ N ii ] , [ S ii ] , [ O i ] ) show a Baldwin relation relative to the broad H \alpha luminosity L _ { \mathrm { bH \alpha } } , with slopes in the range of 0.53 - 0.72 .
2 .
About 20 % of the type 1 AGN reside within the ‘ Composite ’ and ‘ SF ’ regions of the BPT diagrams .
These objects also show excess narrow H \alpha and UV luminosities , for their L _ { \mathrm { bH \alpha } } , consistent with contribution from star formation which dominates the narrow lines emission , as expected from their positions in the BPT diagrams .
3 .
The type 1 which reside within the AGN region in the BPT diagrams , are offset to lower [ S ii ] /H \alpha and [ N ii ] /H \alpha luminosity ratios , compared to type 2 AGN .
This offset is a selection effect , related to the lower AGN/host luminosity selection of the type 2 AGN selected from the SDSS galaxy sample .
4 .
The [ N ii ] /H \alpha and [ N ii ] / [ S ii ] ratios in type 1 AGN increase with the host mass , as expected if the mass-metallicity relation of quiescent galaxies holds for the AGN narrow line region .
5 .
The broad lines optical Fe ii is higher for a higher [ N ii ] /H \alpha , at a fixed L _ { bol } and Eddington ratio L / L _ { Edd } .
This suggests that the broad line region metallicity is also related to the host mass .
6 .
The fraction of AGN which are LINERs increases sharply with decreasing L / L _ { Edd } .
This fraction is the same for type 1 and type 2 AGN .
7 .
The BPT position is unaffected by the amount of dust extinction of the optical-UV continuum , which suggests the extincting dust resides on scales larger than the NLR .