The EUV provides most of the ionization that creates the high equivalent width ( EW ) broad and narrow emission lines ( BELs , NELs ) of quasars .
Spectra of Hypermassive Schwarzschild black holes ( HMBHs , M _ { BH } \geq 10 ^ { 10 } M _ { \odot } ) with \alpha -discs , decline rapidly in the EUV suggesting much lower EWs .
Model spectra for black holes of mass 10 ^ { 6 } -10 ^ { 12 } M _ { \odot } and accretion rates 0.03 \leq L _ { bol } / L _ { edd } \leq 1.0 were input to the CLOUDY photoionization code .
BELs become \sim 100 times weaker in EW from M _ { BH } \sim 10 ^ { 8 } M _ { \odot } to M _ { BH } \sim 10 ^ { 10 } M _ { \odot } .
The high ionization BELs ( O VI 1034 Å , C IV 1549 Å , He II 1640 Å ) decline in EW from ( M _ { BH } \geq 10 ^ { 6 } M _ { \odot } , reproducing the Baldwin effect , but regain EW for M _ { BH } \geq 10 ^ { 10 } M _ { \odot } ) .
The low ionization lines ( MgII 2798 Å , H \beta 4861 Å and H \alpha 6563 Å ) remain weak .
Lines for maximally spinning HMBHs behave similarly .
Line ratio diagrams for the BELs show that high OVI/H \beta and low CIV/H \alpha may pick out HMBH , although OVI is often hard to observe .
In NEL BPT diagrams HMBHs lie among star forming regions , except for highly spinning , high accretion rate HMBHs .
In summary , the BELs expected from HMBHs would be hard to detect using the current optical facilities .
From 100 to 10 ^ { 12 } M _ { \odot } , the emission lines used to detect AGN only have high EW in the 10 ^ { 6 } -10 ^ { 9 } M _ { \odot } window , where most AGN are found .
This selection effect may be distorting reported distributions of M _ { BH } .