A VLBA-uGMRT search for candidate binary black holes: Study of six X-shaped radio galaxies with double-peaked emission lines
arxiv(2024)
摘要
Identifying methods to discover dual AGN has proven to be challenging.
Several indirect tracers have been explored in the literature, including
X/S-shaped radio morphologies and double-peaked (DP) emission lines in the
optical spectra. However, the detection rates of confirmed dual AGN candidates
from the individual methods remain extremely small. We search for binary black
holes in a sample of six sources that exhibit both X-shaped radio morphology
and DP emission lines using the VLBA. Three out of the six sources show dual
VLBA compact components, making them strong candidates for binary black hole
sources. In addition, we present deep uGMRT images revealing the exquisite
details of the X-shaped wings in three sources. We present a detailed
precession modeling analysis of these sources. The BH separations estimated
from the simplistic geodetic precession model are incompatible with those
estimated from emission line offsets and the VLBA separations. However,
precession induced by a noncoplanar secondary black hole is a feasible
mechanism for explaining the observed X-shaped radio morphologies and the black
hole separations estimated from other methods. The black hole separations
estimated from the double-peaked emission lines agree well with the VLBA
compact component separations. Future multi-frequency VLBA observations will be
critical in ruling out or confirming the binary black hole scenario in the
three galaxies with dual component detections.
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