Journal: Transactions of IAA RAS vol. 40
Keywords: VLBI, Transients, galaxy nuclei, active galaxies
It is well established that the merger among gas-rich galaxies can trigger both starbursts and the onset of an active galactic nucleus (AGN). We present results on EVN observations toward the AGN hosts IC 883 and PGC 043234, both mergers although at different stages in their evolution. IC 883 is an advanced merger in which the star formation dominates the global energetics of the system. However, our observations show that the nuclear region is dominated by an AGN that has a core-jet morphology. The core has a very inverted spectrum and a low frequency turnover at 4.4 GHz, indicating this is a young source (∼ 3 × 103 yr). PGC 043234 is a post-starburst galaxy which seems to be the remnant of a merger and has a negligible star formation. This system recently hosted the tidal disruption event (TDE) ASASSN-14li. Our EVN observations have allowed us to resolve the system into two components 2pc apart. The components resemble a core-jet/outflow system, whose secondary component can be related directly to ASASSN-14li, if its motion is superluminal, or to a past AGN flare or TDE if its motion is subluminal. The exciting possibility exists that both components are instead a binary BH system. Can IC 883-like systems become PGC 043234-like systems? Multiwavelength unbiased surveys are needed to directly test this connection, and in particular, we note that VLBI observations can help shedding light into the AGN activity in the different evolutionary stages.