Unveiling the AGN in IC 883: discovery of a parsec-scale radio jet

Abstract

IC 883 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 that provides direct and unequivocal evidence of the AGN activity in IC 883. Our analysis of archival X-ray data, together with the detection of a transient radio source with luminosity typical of bright supernovae, gives 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 0.6-1 c. The AGN contributes less than 2 per cent of the total IR luminosity of the system. The corresponding Eddington factor is ∼10<SUP>-3</SUP>, suggesting this is a low-accretion rate engine, as often found in LLAGNs. However, its high bolometric luminosity (∼10<SUP>44</SUP> erg s<SUP>-1</SUP>) 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 ∼4.4 GHz, thus qualifying as a candidate for the least luminous (L<SUB>5.0 GHz</SUB> ∼ 6.3 × 10<SUP>28</SUP> erg s<SUP>-1</SUP> Hz<SUP>-1</SUP>) and one of the youngest (∼3 × 10<SUP>3</SUP> yr) gigahertz-peaked spectrum (GPS) sources. If the GPS origin for the IC 883 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.