The curious activity in the nucleus of NGC 4151: jet interaction causing variability?

Publication date: 
Main author: 
Williams, D. R. A.
IAA authors: 
Moldón, J.
Williams, D. R. A.;Baldi, R. D.;McHardy, I. M.;Beswick, R. J.;Panessa, F.;May, D.;Moldón, J.;Argo, M. K.;Bruni, G.;Dullo, B. T.;Knapen, J. H.;Brinks, E.;Fenech, D. M.;Mundell, C. G.;Muxlow, T. W. B.;Pahari, M.;Westcott, J.
Monthly Notices of the Royal Astronomical Society
Publication type: 
A key characteristic of many active galactic nuclei (AGN) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ∼50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher-resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35±1.10 to 37.09±1.86 mJy/beam, representing a 8.2σ increase on the MERLIN observations. We attribute this peak flux density increase to continued interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGN such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet-ELR interaction.
ADS Bibcode: 
galaxies: active;galaxies: individual: NGC 4151;galaxies: jets;galaxies: nuclei;quasars: emission lines;galaxies: Seyfert;Astrophysics - Astrophysics of Galaxies;Astrophysics - High Energy Astrophysical Phenomena