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Hypermassive black holes have faint broad and narrow emission lines

Bhat, HK and Chakravorty, S and Sengupta, D and Elvis, M and Datta, SR and Roy, N and Bertemes, C and Ferland, G and Ezhikode, SH (2020) Hypermassive black holes have faint broad and narrow emission lines. In: Monthly Notices of the Royal Astronomical Society, 497 (3). pp. 2992-3010.

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Official URL: https://doi.org/10.1093/mnras/staa2002


The extreme ultraviolet region (EUV) provides most of the ionization that creates the high equivalent width (EW) broad and narrow emission lines (BELs and NELs) of quasars. Spectra of hypermassive Schwarzschild black holes (HMBHs; MBH ≥ 1010 M⊙) with α-discs, decline rapidly in the EUV suggesting much lower EWs. Model spectra for BHs of mass 106-1012 M⊙ and accretion rates 0.03 ≤ Lbol/LEdd ≤ 1.0 were input to the cloudy photoionization code. BELs become ∼100 times weaker in EW from MBH ∼108 M⊙ to MBH ∼1010 M⊙. The high-ionization BELs (O vi 1034 Å, C iv 1549 Å, and He ii 1640 Å) decline in EW from MBH ≥ 106 M⊙, reproducing the Baldwin effect, but regain EW for MBH ≥ 1010 M⊙. The low-ionization lines (Mg ii 2798 Å, H β 4861 Å, and H α 6563 Å) remain weak. Lines for maximally spinning HMBHs behave similarly. Line ratio diagrams for the BELs show that high O vi/H β and low C iv/H α may pick out HMBH, although O vi 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 1012 M⊙, the emission lines used to detect active galactic nuclei (AGNs) only have high EW in the 106-109 M⊙ window, where most AGNs are found. This selection effect may be distorting reported distributions of MBH. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

Item Type: Journal Article
Publication: Monthly Notices of the Royal Astronomical Society
Publisher: Oxford University Press
Additional Information: The copyright for this article belongs to the Author(s).
Keywords: accretion, accretion discs; black hole physics; galaxies: Active; line: Formation; quasars: Emission lines; quasars: Supermassive black holes
Department/Centre: Division of Physical & Mathematical Sciences > Astronomy and Astrophysics Programme
Date Deposited: 13 Jan 2023 05:01
Last Modified: 13 Jan 2023 05:01
URI: https://eprints.iisc.ac.in/id/eprint/79083

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