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 $M_{BH}$.

中文翻译：

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超大质量黑洞具有微弱的宽窄发射线

EUV 提供大部分电离，产生类星体的高等效宽度 (EW) 宽发射线和窄发射线 (BEL、NEL)。超大质量史瓦西黑洞（HMBH，$M_{BH} \geq 10^{10} M_{\odot}$）的光谱在 EUV 中迅速下降，表明 EW 低得多。质量为 $10^{6}-10^{12} M_{\odot}$ 的黑洞模型光谱和吸积率为 $0.03 \leq L_{bol}/L_{edd} \leq 1.0$ 被输入到 CLOUDY 光电离代码. 在 EW 中，BEL 从 $M_{BH} \sim 10^8 M_{\odot}$ 到 $M_{BH} \sim 10^{10} M_{\odot}$ 变弱了 $\sim$100 倍。高电离 BEL (O VI 1034 $\overset{\circ}{\mathrm {A}}$, C IV 1549 $\overset{\circ}{\mathrm {A}}$, He II 1640 $\overset{ \circ}{\mathrm {A}}$) 的 EW 从 ($M_{BH} \geq 10^6 M_{\odot}$ 下降，再现鲍德温效应，但以 $M_{BH} \geq 10^{10} M_{\odot}$ 重新获得 EW）。低电离线（MgII 2798 $\overset{\circ}{\mathrm {A}}$, H$\beta$ 4861 $\overset{\circ}{\mathrm {A}}$ 和 H$\alpha$ 6563 $\overset{\circ}{\mathrm {A}}$) 仍然疲软。最大旋转 HMBH 的线条表现类似。BEL 的线比图显示高 OVI/H$\beta$ 和低 CIV/H$\alpha$ 可能会挑出 HMBH，尽管 OVI 通常很难观察到。在 NEL BPT 图中，HMBH 位于恒星形成区域之间，除了高度旋转、高吸积率的 HMBH。总之，使用当前的光学设备很难检测到来自 HMBH 的 BEL。从 100 到 $10^{12} M_{\odot}$，用于检测 AGN 的发射线仅在 $10^6 - 10^9 M_{\odot}$ 窗口中具有高 EW，在该窗口中可以找到大多数 AGN。