As part of a long-term project to study the effects of nuclear activity on the surrounding environment, we recently obtained deep TAURUS-2 data at the AAT on the Circinus galaxy, the nearest (~4 Mpc) Seyfert 2 galaxy known. The new data on Circinus show for the first time a complex of ionized filaments extending radially from the nucleus out to distances of 1 kpc. Arcs suggestive of bow shocks are observed at the terminus of some of these filamentary structures. Most spectacular of all, one of the structures appears to be a scaled-up version of a Herbig-Haro jet which extends to ~800 pc west of the nucleus (Figure below).
The kinematics derived from the TAURUS-2 data and from long-slit spectra kindly obtained by Stuart Lumsden with the RGO spectrograph on the AAT bring credence to this nuclear outflow scenario. The filaments appear to represent material expelled from the nucleus (possibly in the form of `bullets') or entrained in a wide-angle wind roughly aligned with the polar axis of the galaxy. Extrapolation of these filaments to smaller radii comes to within 1 arcsec (about 20 pc) of the infrared nucleus, therefore suggesting an AGN or nuclear starburst origin to these features.
The complex of radial filaments and bow shocks detected in the Circinus galaxy is unique amongst active galaxies. The frequency of such events is unknown since only a handful of active galaxies have been observed at the sensitivity level of our present observations. The discovery of these features in the Circinus galaxy, a spiral galaxy with an abnormal richness of gas, brings up the possibility that we may be witnessing a common evolutionary phase in the lives of gas-rich active galaxies during which the dusty cocoon surrounding the nucleus is expelled by the combined action of jet and wind phenomena. Observations of other active galaxies at similar sensitivity will help establish the frequency and duration of this phenomenon.
Sylvain Veilleux (University of Maryland) and Joss Bland Hawthorn (AAO)