Jet-powered Outflows in Supermassive Black Hole Binary Candidate SDSS J1048+0055
2019
The search and study of close pairs of
supermassive black holes(SMBHs) is important in the study of
galaxy mergerswhich can possibly trigger
active galactic nucleus(AGN) activity, and in the context of their evolution into the gravitational wave emitting regime. The quasar SDSS~J1048+0055 was identified as a SMBH binary candidate based on the observed double-peaked \OIII$\lambda\lambda$4959,5007 emission lines and two distinct radio components separated by $\sim 20$~pc \citep{2004ApJ...604L..33Z}. To ascertain the binary nature of this source, we analyzed multi-frequency, multi-epoch
very long baseline interferometry(VLBI) data to investigate its pc-scale radio properties. The source shows double components with the western feature being brighter than the eastern one. This brighter component has a
brightness temperatureof $\sim 10^{10}$~K,
spectral indexof $\alpha = -0.09 \pm 0.09$ (flat) and is indicative of mildly
relativistic beaming. In contrast, the faint component has a lower
brightness temperatureof $\sim 10^{8-9}$~K and steep spectrum. These clues are consistent with a core--jet structure, moreover, the apparent separation speed between the two components is much higher than the expected
orbital motionin a binary SMBH. Thus the present study excludes the association of the two VLBI components with the cores of a SMBH binary, although the SMBH binary possibility (e.g., a pair of radio-loud and radio-quiet AGNs) is not fully ruled out. In the single
active galactic nucleus(AGN) scenario, the double-peaked optical emission lines can originate from the jet interacting with the narrow-line region as indicated by a change in the jet direction at $\sim$ 140 pc.
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