Hypermassive black holes have faint broad and narrow emission lines

Author:

Bhat Harshitha K123,Chakravorty Susmita4,Sengupta Dhrubojyoti5,Elvis Martin6,Datta Sudeb Ranjan4,Roy Nirupam4,Bertemes Caroline7ORCID,Ferland Gary8,Ezhikode Savithri H9

Affiliation:

1. Department of Physics, St. Joseph’s College, 36 Lalbagh Road, Bangalore 560027, India

2. I.Physikalisches Institut der Universität zu Köln, Zülpicher Str 77, D-50937 Köln, Germany

3. Max-Plank-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

4. Department of Physics, Indian Institute of Science, Bangalore 560012, India

5. Presidency University, 86/1 College Street, Kolkata 700073, India

6. Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

7. Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK

8. Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA

9. Inter-University Centre for Astronomy & Astrophysics (IUCAA), Ganeshkhind, Pune 411007, India

Abstract

ABSTRACT 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.

Funder

Indian Institute of Science

Science and Engineering Research Board

Infosys Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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