The nuclear outflow in NGC 2110

Abstract

We present a spectroscopic and optical/radio imaging study of the Seyfert NGC 2110 using the Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS), aiming to measure the dynamics and understand the nature of the nuclear outflow in the galaxy. Previous HST studies have revealed the presence of a linear structure in the narrow-line region (NLR) aligned with the radio jet. We show that this structure is strongly accelerated, probably by the jet, but is unlikely to be entrained in the jet flow. The ionization properties of this structure are consistent with photoionization of dusty, dense gas by the active nucleus. We present a plausible geometrical model for the NLR, bringing together various components of the nuclear environment of the galaxy. We highlight the importance of the circumnuclear disc in determining the appearance of the emission-line gas and the morphology of the jet. From the dynamics of the emission-line gas, we place constraints on the accelerating mechanism of the outflow and discuss the relative importance of radio source synchrotron pressure, radio jet ram pressure and nuclear radiation pressure in accelerating the gas. While all three mechanisms can account for the energetics of the emission-line gas, gravitational arguments support radio jet ram pressure as the most likely source of the outflow.