http://arxiv.org/abs/1908.01799
We present a method for comparing the H$\beta$ emission-line profiles of observed supermassive black hole (SBHB) candidates and models of sub-parsec SBHBs in circumbinary disks. Using the approach based on principal component analysis we infer the values of the binary parameters for the spectroscopic SBHB candidates and evaluate the parameter degeneracies, representative of the uncertainties intrinsic to such measurements. We find that as a population, the SBHB candidates favor the average value of the semimajor axis corresponding to $\log(a/M) \approx 4.20\pm 0.42$ and comparable mass ratios, $q>0.5$. If the considered SBHB candidates are true binaries, this result would suggest that there is a physical process that allows initially unequal mass systems to evolve toward comparable mass ratios or point to some, yet unspecified, selection bias. Because the orbital eccentricity suffers from a large degree of degeneracy, we obtain no useful constraints on this parameter. Our method also indicates that the SBHB candidates do not favor configurations in which the mini-disks are coplanar with the binary orbital plane. If upheld for confirmed SBHBs, this finding would indicate the presence of a physical mechanism that maintains misalignment of the mini-disks (or causes them to be warped) down to sub-parsec binary separations. The probability distributions for most of the SBHB parameters inferred for the observed SBHB candidates and our control group of AGNs are statistically indistinguishable, implying that this method can in principle be used to interpret the observed emission-line profiles once a sample of confirmed SBHBs is available but cannot be used as a conclusive test of binarity.
K. Nguyen, T. Bogdanovic, J. Runnoe, et. al.
Wed, 7 Aug 19
61/61
Comments: Submitted to ApJ (29 pages, 18 figures)
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