Evidence of jet-clump interaction: a flip of the radio jet head of 3C~84

TL;DR

This study observes a flip in the radio jet component of 3C 84, supporting models of jet interaction with clumpy environments, and estimates the density of the interacting clump.

Contribution

First direct observation of a jet flip in 3C 84 consistent with hydrodynamical simulations of jet-clump interactions.

Findings

Detected a 0.4 mas flip in jet component C3.

Observed C3's flux density increase during the event.

Estimated clump density to be 10^{3-5} cm^{-3}.

Abstract

Radio jets in active galaxies have been expected to interact with circumnuclear environments in their early phase evolutions. By performing the multi-epoch monitoring observation with the KVN and VERA Array (KaVA) at 43~GHz, we investigate the kinematics of the notable newborn bright component C3 located at the tip of the recurrent jet of 3C~84. During 2015 August-September, we discover the flip of C3 and the amount of the flip is about 0.4~milli-arcsecond in angular scale, which corresponds to 0.14 parsec in physical scale. After the flip of C3, it wobbled at the same location for a few months and then it restarted to propagate towards the southern direction. The flux density of C3 coherently showed the monotonic increase during the observation period. The flip is in good agreement with hydrodynamical simulations of jets in clumpy ambient medium. We estimate the number density of the putative clump based on the momentum balance between the jet thrust and the ram pressure from the clump and it is about $10^{3-5}~{\rm cm^{-3}}$. We briefly discuss possible origins of the clump.