paper

Rejection of the Binary Broad-Line Region Interpretation of Double-Peaked Emission Lines in Three Active Galactic Nuclei

arXiv:astro-ph/9706222 · doi:10.1086/304859

Abstract

It has been suggested that the peculiar double-peaked Balmer lines of certain broad-line radio galaxies come from individual broad-line regions associated with the black holes of a supermassive binary. We continue to search for evidence of the radial velocity variations characteristic of a double-lined spectroscopic binary that are required in such a model. After spectroscopic monitoring of three suitable candidates (Arp 102B, 3C 390.3, and 3C 332) spanning two decades, we find no such long-term systematic changes in radial velocity. A trend noticed by Gaskell in one of the Balmer-line peaks of 3C 390.3 before 1988 did not continue after that year, invalidating his inferred orbital period and mass. Instead, we find lower limits on the plausible orbital periods that would require the assumed supermassive binaries in all three objects to have total masses in excess of 10^10 solar masses. In the case of 3C 390.3 the total binary mass must exceed 10^11 solar masses to satisfy additional observational constraints on the inclination angle. Such large binary black hole masses are difficult to reconcile with other observations and with theory. In addition, there are peculiar properties of the line profiles and flux ratios in these objects that are not explained by ordinary broad-line region cloud models. We therefore doubt that the double-peaked line profiles of the three objects arise in a pair of broad-line regions. Rather, they are much more likely to be intimately associated with a single black hole.

arXiv commentTo appear in the Astrophysical Journal. 17 pages, TeX, with postscript figures includedes

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