IC 5063: AGN driven outflow of warm and cold gas

Abstract

We present new ATCA 17- and 24-GHz radio images and ESO-NTT optical spectra of the radio-loud Seyfert galaxy IC 5063, the first galaxy in which a fast (~600 km s-1) outflow of neutral hydrogen was discovered. The new radio data confirm the triple radio structure with a central, unresolved flat-spectrum core and two resolved radio lobes with steep spectral index. This implies that the previously detected fast outflow of neutral gas is occurring off-nucleus, near a radio lobe about 0.5 kpc from the core. The ionised gas shows highly complex kinematics in the region co-spatial with the radio emission. Broad and blueshifted (~500 km s-1) emission is observed in the region of the radio lobe, at the same location as the blueshifted H I absorption. The velocity of the ionised outflow is similar to the one found in H I. The first order correspondence between the radio and optical properties suggests that the outflow is driven by the interaction between the radio jet and the ISM. However, despite the high outflow velocities, no evidence is found for the ionisation of the gas being due to fast shocks in the region of the outflow, indicating that photoionisation from the AGN is likely to be the dominant ionisation mechanism. The outflow rate of the warm (ionised) gas is small compared to that of the cold gas, similar to what is found in other radio galaxies. The mass outflow rate associated with the H I is in the same range as for “mild” starburst-driven superwinds in ULIRGs. However, in IC 5063, the AGN-driven outflow appears to be limited to the inner kpc region of the galaxy. The kinetic power associated with the H I outflow is a small fraction (a few ×10-4) of the Eddington luminosity of the galaxy but is a significant fraction (~0.1) of the nuclear bolometric luminosity. In IC 5063, the observed outflows may have sufficient kinetic power to have a significant impact on the evolution of the ISM in the host galaxy.

Based on observations with the ESO-NTT and with the Australia Telescope Compact Array.