`Zwicky's Nonet': a compact merging ensemble of nine galaxies and 4C
  35.06, a peculiar radio galaxy with dancing radio jets
  We report the results of our radio, optical and infra-red studies of a
peculiar radio source 4C~35.06, an extended radio-loud AGN at the center of
galaxy cluster Abell 407 ($z=0.047$). The central region of this cluster hosts
a remarkably tight ensemble of nine galaxies, the spectra of which resemble
those of passive red ellipticals, embedded within a diffuse stellar halo of
$\sim$1~arcmin size. This system (named the `Zwicky's Nonet') provides unique
and compelling evidence for a multiple-nucleus cD galaxy precursor.
Multifrequency radio observations of 4C~35.06 with the Giant Meterwave Radio
Telescope (GMRT) at 610, 235 and 150 MHz reveal a system of 400~kpc scale
helically twisted and kinked radio jets and outer diffuse lobes. The outer
extremities of jets contain extremely steep spectrum (spectral index -1.7 to
-2.5) relic/fossil radio plasma with a spectral age of a few$\,\times (10^7 -
10^8)$ yr. Such ultra-steep spectrum relic radio lobes without definitive
hot-spots are rare, and they provide an opportunity to understand the
life-cycle of relativistic jets and physics of black hole mergers in dense
environments. We interpret our observations of this radio source in the context
of the growth of its central black hole, triggering of its AGN activity and jet
precession, all possibly caused by galaxy mergers in this dense galactic
system. A slow conical precession of the jet axis due to gravitational
perturbation between interacting black holes is invoked to explain the unusual
jet morphology.
