Session 7: Observational Astronomy

Title: The central engine of the powerful and unusual radio galaxy Hercules A
Author(s): N. A. B. Gizani, M. A. Garrett, J. P. Leahy (Oral)

We present the most recent results from the analysis of the radio data on the pc-scale structure of the powerful extragalactic radio source Hercules A, observed at 18 cm using the EVN-MERLIN array. A faint but compact radio source, coincident with the optical centre of Hercules A was detected by EVN at 0.018 arcs resolution. The flux of the radio core with EVN is 14.6 mJy. Its angular size is 18.1x7.0 mas with a position angle of ~ 139.3o. Its brightness temperature is 2x107 K. We have found that Hercules A is asymmetric on pc-scales: There is a SE emission, most probably from the eastern pc-scale jet, due to Doppler boosting. We conclude that if this is indeed the case then there is a misalignment between the pc- and kpc-scale jet (at least the eastern one) of 35o. This is quite unusual and may give us information about a dense opaque intergalactic/interstellar medium. MERLIN got confused by the diffuse radio structure of the radio galaxy.