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Astron. Astrophys. 344, 767-778 (1999)

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A molecular outflow in the Circinus galaxy *

S.J. Curran, G. Rydbeck, L.E.B. Johansson and R.S. Booth

Onsala Space Observatory, Chalmers University of Technology, S-439 92 Onsala, Sweden (sjc@oso.chalmers.se)

Received 12 October 1998 / Accepted 21 January 1999

Abstract

From previous work on the Circinus galaxy we postulated that [FORMULA] of the molecular gas in this type 2 Seyfert nucleus is distributed in a sub-kiloparsec circumnuclear ring, probably associated with the ongoing star-burst. In addition to this, we postulated the possible presence of a molecular outflow along the galaxy's minor axis. In this work we use a modified version of the routine used previously (Curran et al. 1998), in order to model this feature. From our results we believe that a 90o wide outflow, which constitutes [FORMULA] of the molecular gas within the central [FORMULA] pc, extends to a distance of [FORMULA] pc along the rotation axis of the ring with a maximum velocity of [FORMULA] [FORMULA]. The bulk velocity, which is somewhat lower than this, gives an estimate of [FORMULA][FORMULA] for the mechanical luminosity of the outflow. Armed with a model of the molecular gas distribution, and the fact that the large scale molecular ring appears to be perpendicular to the outflow/radio jets, we modelled how the CO luminosity varies with ring and outflow inclination i.e. Seyfert type. Our results show that in the case of a ring+outflow system, we expect very little difference in the luminosities of a face-on and an identical edge-on system. In the case of a ring only distribution however, we do expect, due to "hole" in the gas, slightly more emission from a sufficiently close edge-on system, but still not enough to account for the differences in CO luminosities which have been observed between type 1 and type 2 Seyferts. This result supports the notion that something more than mere orientation comes into play when explaining these differences, thus having major implications for the unified theories of active galactic nuclei.

Key words: Galaxy: evolution – galaxies: active – galaxies: individual: Circinus galaxy – galaxies: ISM – galaxies: kinematics and dynamics

* Based on results collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: S. Curran

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© European Southern Observatory (ESO) 1999

Online publication: March 29, 1999
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