Double-peaked line profiles in AGNs testing for supermassive binary black holes

One model for double‐peaked emission lines in AGNs is the double‐lined spectroscopic binary consisting of two black holes, each with its own broad‐lineregion. We are continuing to monitor the Hα line profiles of the two AGNs which will provide the most sensitive test of this theory. Arp 102B and 3C 332. The absence of orbital motion can be translated into a lower limit on the mass of the hypothesized binary. As of 1991, we have obtained lower limits of 4×109M⊙ and 2×1010 M⊙ for Arp 102B and 3C 332, respectively, rendering this theory highly unlikely. We cannot rule out the existence of a supermassitve binary, but only the model in which the emission‐line peaks are attributed to the two different nuclei. Alternatively, long‐term monitoring might reveal small‐amplitude radial velocity variations to an unseen companion.