IDENTIFYING SUPERMASSIVE BLACK HOLE BINARIES WITH BROAD EMISSION LINE DIAGNOSIS
IDENTIFYING SUPERMASSIVE BLACK HOLE BINARIES WITH BROAD EMISSION LINE DIAGNOSIS
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DOI：
10.1088/0004-637x/725/1/249
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发表时间：
2009-12
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影响因子：
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通讯作者：
Yue Shen;A. Loeb
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作者：
Yue Shen;A. Loeb
活动星系核中的双峰宽发射线可能表明存在一个束缚超大质量黑洞（SMBH）双星，其中两个不同的宽线区（BLR）共同贡献的线轮廓。另一种解释是一个磁盘发射源的双峰线轮廓。使用简单的BLR模型，我们计算出预期的宽线轮廓SMBH二进制在不同的分离。在合理的假设下，这两个BLR是由两个活跃的SMBH照明和BLR位置的电离通量是大致恒定的，我们确认出现双峰的功能和径向速度漂移的两个峰值，由于二进制轨道运动。然而，这种明显的双峰特征只出现在双星演化的特定阶段，当两个黑洞（BH）足够接近，使得视线轨道速度差大于单个宽分量的FWHM时，而两个BLR仍然是不同的。在此阶段之前，由于双星轨道运动的速度分裂太小，无法将两个BLR的发射分开，导致一般不对称的宽线轮廓。当两个黑洞更接近，使得两个BLR不再是不同的，线轮廓变得更加复杂，峰的分裂不对应于双星的轨道运动。在这种情况下，有没有相干的径向速度漂移的峰值随时间的推移。不对称的线轮廓可能是一个更常见的签名二进制SMBH比双峰轮廓。我们讨论了时间变化的宽线轮廓的二进制SMBH和突出的混响映射的不同行为的二进制和磁盘发射器的情况下，这可能是一个可行的工具来解开这两种情况。
Double-peaked broad emission lines in active galactic nuclei may indicate the existence of a bound supermassive black hole (SMBH) binary where two distinct broad-line regions (BLRs) contribute together to the line profile. An alternative interpretation is a disk emitter origin for the double-peaked line profile. Using simple BLR models, we calculate the expected broad line profile for an SMBH binary at different separations. Under reasonable assumptions that both BLRs are illuminated by the two active SMBHs and that the ionizing flux at the BLR location is roughly constant, we confirm the emergence of double-peaked features and radial velocity drifts of the two peaks due to the binary orbital motion. However, such a clear double-peaked feature only arises in a particular stage of the binary evolution when the two black holes (BHs) are close enough such that the line-of-sight orbital velocity difference is larger than the FWHM of the individual broad components, while the two BLRs are still mostly distinct. Prior to this stage, the velocity splitting due to the orbit motion of the binary is too small to separate the emission from the two BLRs, leading to asymmetric broad line profiles in general. When the two BHs are even closer such that the two BLRs can no longer be distinct, the line profile becomes more complex and the splitting of the peaks does not correspond to the orbital motion of the binary. In this regime, there are no coherent radial velocity drifts in the peaks with time. Asymmetric line profiles are probably a far more common signature of binary SMBHs than double-peaked profiles. We discuss the temporal variations of the broad line profile for binary SMBHs and highlight the different behaviors of reverberation mapping in the binary and disk emitter cases, which may serve as a feasible tool to disentangle these two scenarios.