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 $overset{circ}{mathrm {A}}$, C IV 1549 $overset{circ}{mathrm {A}}$, He II 1640 $overset{circ}{mathrm {A}}$) 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 $overset{circ}{mathrm {A}}$, H$beta$ 4861 $overset{circ}{mathrm {A}}$ and H$alpha$ 6563 $overset{circ}{mathrm {A}}$) 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 $M_{BH}$.
Download