Volume 439, Number 3, September I 2005
|Page(s)||947 - 956|
|Published online||12 August 2005|
Extra-planar gas in the spiral galaxy NGC 4559
INAF – Osservatorio Astronomico, via Ranzani 1, 40127 Bologna, Italy e-mail: email@example.com
2 Università degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, 20133 Milano, Italy
3 Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK
4 ASTRON, PO Box 2, 7990 AA, Dwingeloo, The Netherlands
5 Kapteyn Astronomical Institute, University of Groningen, The Netherlands
Accepted: 15 April 2005
We present 21-cm line observations of the spiral galaxy NGC 4559, made with the Westerbork Synthesis Radio Telescope. We have used them to study the H I distribution and kinematics, the relative amount and distribution of luminous and dark matter in this galaxy and, in particular, the presence of extra-planar gas. Our data do reveal the presence of such a component, in the form of a thick disk, with a mass of (one tenth of the total H I mass) and a mean rotation velocity 25-50 km s-1 lower than that of the thin disk. The extra-planar gas may be the result of galactic fountains but accretion from the IGM cannot be ruled out. With this study we confirm that lagging, thick H I layers are likely to be common in spiral galaxies.
Key words: galaxies: halos / galaxies: individual: NGC 4559 / galaxies: ISM / galaxies: kinematics and dynamics
© ESO, 2005
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