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Astron. Astrophys. 333, 459-465 (1998)

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1. Introduction

Disturbed morphologies of ionized nebulosities surrounding active galactic nuclei are frequently observed, mainly in high ionization gas. The morphology is usually interpreted in terms of a conical or biconical shape centered on the nucleus. The spectacular ionizing cone discovered in NGC 5252 by Tadhunter & Tsvetanov (1989) is thought to arise from interstellar matter lit up by radiation from the nuclear non stellar continuum escaping the central regions through the hole of an obscuring torus surrounding the nucleus. The situation is far less clear in the other reported cases where the cone may be seen only on one side of the nucleus or has less marked edges (cf Wilson & Tsvetanov 1994 for a review). The possibility of having outflows or inflows in cones centered on the nucleus has been invoked to account for the kinematical properties of several Seyferts (e.g. Wilson et al. 1985), but kinematics have been studied in detail only in a few of the Seyferts which show evidence for galactic outflows.

In this paper we present new results on the kinematics of the ionized gas in the highly inclined ([FORMULA]) Sa Seyfert galaxy NGC 2992, crossed by a disturbed dust lane oriented along the major axis ([FORMULA], RC3 catalogue). This edge-on galaxy is connected by a tidal tail to a close companion, NGC 2993, at a projected distance of 2.9 arcmin (35.5 kpc for H0 =50 km s-1 Mpc-1) and with a 109 km s-1 velocity difference (see RC3 catalog), which may well have important perturbing effects on its dynamics. Combined optical broad and narrow band images reveal a complex structure (Durret & Bergeron 1987, Wehrle & Morris 1988). The [OIII] and H [FORMULA] images show an arc of emission southeast of the nucleus (which could be interpreted as HII regions in the spiral arm) as well as a finger of emission emerging from the northwest portion of the nucleus, pointing northward. At 20cm radio wavelength, NGC 2992 reveals a radio source of total extent 25 arcsec and major axis PA [FORMULA], with a one-sided extension along PA [FORMULA] (Ward et al, 1980; Hummel et al., 1983). At smaller scale an 8-shaped structure, with the nucleus at the crossing-point, is visible at 6cm along PA= [FORMULA] and interpreted as limb-brightened bubbles or magnetic arches (Ulvestad & Wilson 1984; Wehrle & Morris 1988). A comparison of the line emission images with the radio images shows no correlation.

Colina et al. (1987) have mapped NGC 2992 by using long slit spectroscopy roughly along the major axis and the two axes given by the high resolution radio map by Ulvestad & Wilson (1984). From their kinematical data in the [OIII] lines, they observe blue asymmetric profiles only in the very center of the galaxy. They find that the nuclear and off-nuclear regions are dynamically decoupled, and suggest that there are non-circular motions due to radial flows and tidal interaction with NGC 2993. They interpret their data as being consistent with a radial outflow of gas in a plane which is not coaligned with the galactic plane, rather than outflow within a cone. On the contrary, Tsvetanov et al. (1995) describe NGC 2992 as a good candidate for having large-scale minor axis outflows with velocities up to 200 km s-1.

Since NGC 2992 is a highly inclined object, it is a good candidate to sample gas motions out of the disk plane. In the following, we present a first order kinematic model of the ionized gas in NGC 2992, based on a set of long slit spectra.

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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998