Unveiling the AGN in IC 883: discovery of a parsec-scale radio jet
  IC883 is a luminous infrared galaxy (LIRG) classified as a starburst-active
galactic nucleus (AGN) composite. In a previous study we detected a
low-luminosity AGN (LLAGN) radio candidate. Here we report on our radio
follow-up at three frequencies which provides direct and unequivocal evidence
of the AGN activity in IC883. Our analysis of archival X-ray data, together
with the detection of a transient radio source with luminosity typical of
bright supernovae, give further evidence of the ongoing star formation
activity, which dominates the energetics of the system. At sub-parsec scales,
the radio nucleus has a core-jet morphology with the jet being a newly ejected
component showing a subluminal proper motion of 0.6c-1c. The AGN contributes
less than two per cent of the total IR luminosity of the system. The
corresponding Eddington factor is ~1E-3, suggesting this is a low-accretion
rate engine, as often found in LLAGNs. However, its high bolometric luminosity
(~10E44erg/s) agrees better with a normal AGN. This apparent discrepancy may
just be an indication of the transition nature of the nucleus from a system
dominated by star-formation, to an AGN-dominated system. The nucleus has a
strongly inverted spectrum and a turnover at ~4.4GHz, thus qualifying as a
candidate for the least luminous (L_5.0GHz ~ 6.3E28erg/s/Hz) and one of the
youngest (~3000yr) gigahertz-peaked spectrum (GPS) sources. If the GPS origin
for the IC883 nucleus is confirmed, then advanced mergers in the LIRG category
are potentially key environments to unveil the evolution of GPS sources into
more powerful radio galaxies.
