The flickering nuclear activity of Fornax A
  We present new observations of Fornax A taken at 1 GHz with the MeerKAT
telescope and at 6 GHz with the Sardinia Radio Telescope (SRT). The sensitive
(noise ~16 micro-Jy beam$^{-1}$), high resolution ( < 10'') MeerKAT images show
that the lobes of Fornax A have a double-shell morphology, where dense
filaments are embedded in a diffuse and extended cocoon. We study the spectral
properties of these components by combining the MeerKAT and SRT observations
with archival data between 84 MHz and 217 GHz. For the first time, we show that
multiple episodes of nuclear activity must have formed the extended radio
lobes. The modelling of the radio spectrum suggests that the last episode of
injection of relativistic particles into the lobes started ~ 24 Myr ago and
stopped approximately 12 Myr ago. More recently (~ 3 Myr ago), a less powerful
and short ( < 1 Myr) phase of nuclear activity generated the central jets.
Currently, the core may be in a new active phase. It appears that Fornax A is
rapidly flickering. The dense environment in which Fornax A lives has lead to a
complex recent merger history for this galaxy, including mergers spanning a
range of gas contents and mass ratios, as shown by the analysis of the galaxy's
stellar- and cold-gas phases. This complex recent history may be the cause of
the rapid, recurrent nuclear activity of Fornax A.
