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Issue A&A Volume 431, Number 1, February III 2005 Page(s) 65 - 72 Section Extragalactic astronomy DOI 10.1051/0004-6361:20041715

A&A 431, 65-72 (2005)
DOI: 10.1051/0004-6361:20041715

Extra-planar H I in the starburst galaxy NGC 253

R. Boomsma¹, T. A. Oosterloo², F. Fraternali^{3, 2}, J. M. van der Hulst¹ and R. Sancisi<sup>4, 1

1</sup>  Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
    e-mail: boomsma@astro.rug.nl
²  ASTRON, Dwingeloo, The Netherlands
³  Theoretical Physics, University of Oxford, UK
⁴  INAF - Osservatorio Astronomico di Bologna, Bologna, Italy

(Received 22 July 2004 / Accepted 23 September 2004)

Abstract
Observations of the nearby starburst galaxy NGC 253 in the 21-cm line reveal the presence of neutral hydrogen in the halo, up to 12 kpc from the galactic plane. This extra-planar H I is found in only one half of the galaxy and is concentrated in a half-ring structure and plumes which are lagging in rotation with respect to the disk. The H I plumes are seen bordering the bright H and X-ray halo emission. It is likely that, as proposed earlier for the H and the X-rays, the origin of the extra-planar H I is also related to the central starburst and to the active star formation in the disk. A minor merger and gas accretion are also discussed as possible explanations. The H I disk is less extended than the stellar disk. This may be the result of ionization of its outer parts or, alternatively, of tidal or ram pressure stripping.

Key words: galaxies: individual: NGC 253 -- galaxies: ISM -- galaxies: halos -- galaxies: structure

© ESO 2005

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