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Astron. Astrophys. 333, 466-470 (1998)

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Kinematics of the dusty circumnuclear ring in the barred Seyfert galaxy NGC 4151

M.W. Asif 1, 2, C.G. Mundell 2, 3, A. Pedlar 2, S.W. Unger 1, A. Robinson 4, B. Vila-Vilaró 5 and J.R. Lewis 6

1 Isaac Newton Group, Apartado 321, 38780 Santa Cruz de La Palma, Tenerife, Canary Islands, Spain
2 Nuffield Radio Astronomy Laboratories, University of Manchester, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, UK
3 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
4 Division of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
5 Nobeyama Radio Observatory, Nagano 384-13, Japan
6 Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0HA, UK

Received 8 September 1997 / Accepted 19 January 1998

Abstract

We present optical and neutral hydrogen observations of the central [FORMULA] 2 kpc in NGC 4151, and examine the distribution and kinematics of neutral hydrogen in the vicinity of the optical circumnuclear dust `ellipse'. The V-I colour map, derived from broad-band images obtained using TAURUS II in imaging mode, shows clearly the red arcs which delineate the [FORMULA] dust ellipse detected previously.

The new, high resolution ([FORMULA]) HI image reveals two arcs of HI emission, which lie on the inner edges of the main bar and coincide closely with the optical arcs. The peak column densities in the HI arcs, of [FORMULA] cm-2 and [FORMULA] cm-2, imply optical extinctions of [FORMULA] [FORMULA] 1.16 and 0.45 in the northern and southern arcs respectively, which are comparable with those derived from broad-band imaging.

The kinematics of the HI, measured along the two arcs, are presented. The first order circular fit to the velocity curve yields a value of [FORMULA] for the PA of the line of nodes, which agrees well with that of the galaxy. If the HI is associated with the optical ellipse, the PA of the spatial major axis of the ellipse ([FORMULA]) is offset from its kinematic major axis ([FORMULA]), providing evidence of non-circular orbits and suggesting that ring is not an inclined circular disk, but is intrinsically elliptical and lies in the plane of the galaxy.

Key words: galaxies: active; Seyfert; kinematics and dynamics; individual: NGC 4151

Send offprint requests to: M.W. Asif, at La Palma address

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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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