Quantifying the cool ISM in radio AGNs: evidence for late-time
  re-triggering by galaxy mergers and interactions
  We use deep Herschel observations of the complete 2Jy sample of powerful
radio AGNs in the local universe (0.05 < z < 0.7) to probe their cool
interstellar medium (ISM) contents and star-forming properties, comparing them
against other samples of nearby luminous AGNs and quiescent galaxies. This
allows us to investigate triggering and feedback mechanisms. We find that the
dust masses of the strong-line radio galaxies (SLRGs) in our sample are similar
to those of radio-quiet quasars, and that their median dust mass (Mdust = 2 x
10^7 Msun) is enhanced by a factor ~200 compared to that of non-AGN
ellipticals, but lower by a factor ~16 relative to that of local ultra-luminous
infrared galaxies (UILRGs). Along with compelling evidence for merger
signatures in optical images, the SLRGs in our sample also show relatively high
star-formation efficiencies, despite the fact that many of them fall below the
main sequence for star forming galaxies. Together, these results suggest that
most of our SLRGs have been re-triggered by late-time mergers that are
relatively minor in terms of their gas contents. In comparison with the SLRGs,
the radio AGNs with weak optical emission lines (WLRGs) and edge-darkened radio
jets (FRIs) have both lower cool ISM masses and star-formation rates (by a
factor of >30), consistent with being fuelled by a different mechanism (e.g.
the direct accretion of hot gas).
