Journal Article

Search for sub-parsec massive binary black holes through line diagnosis

C. Montuori, M. Dotti, M. Colpi, R. Decarli and F. Haardt

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 1, pages 26-32
Published in print March 2011 | ISSN: 0035-8711
Published online March 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17888.x
Search for sub-parsec massive binary black holes through line diagnosis

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We investigate the spectral properties of an active black hole, member of a massive (107–109 M) sub-parsec black hole binary. We work under the hypothesis that the binary, surrounded by a circumbinary disc, has cleared a gap, and that accretion occurs on to the secondary black hole fed by material closer to the inner edge of the disc. Broad line emission clouds orbit around the active black hole and suffer erosion due to tidal truncation at the Roche Lobe surface, following gap opening and orbital decay. We consider three of the most prominent broad emission lines observed in the spectra of active galactic nuclei (AGNs), i.e. C iv, Mg ii and Hβ, and compute the flux ratios between the lines of Mg ii and C iv () and those of Mg ii and Hβ (). We find that close black hole binaries have up to 1 order of magnitude smaller than single black holes. By contrast may be significantly reduced only at the shortest separations. Peculiarly low values of line flux ratios together with large velocity offsets between the broad and narrow emission lines and/or periodic variability in the continuum (on time-scales ≳ years) would identify genuine sub-pc binary candidates.

Keywords: black hole physics; galaxies: kinematics and dynamics; galaxies: nuclei; quasars

Journal Article.  5556 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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