SDSS J153636.22+044127.0 and Its Analogs: Shocked Outflows, Not Active Binary Black Holes

Abstract

The binary emission-line system, particularly the binary broad-line emission system, is considered the most effective indicator of the black hole binary. A plausible example of such a system, SDSS J153636.22+044127.0, was reported as the first known object with two hydrogen Balmer broad-line systems, which are interpreted to be the result of broad-line regions around a pair of black holes. Here, we show the follow-up optical and near-infrared spectral observations of SDSS J153636.22+044127.0 and its analogs. In these objects, the broad hydrogen Balmer and Paschen, He i , and Mg ii lines share the same peculiar emission-line profile (including a blue system, a red system, and a double-peaked disk-line component); however, the invariance in the large time interval, the absence of the blue system in He i λ 10830 profile, and the abnormally strong emission of the hydrogen Pa β blue system oppose the binary proposal. We suggest that these unique broad lines arise from the active galactic nucleus emission-line region and the shock-heated outflowing gases rather than a binary system of two active black holes.