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Astron. Astrophys. 349, 1-6 (1999)

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Dark matter in the dwarf galaxy NGC 247

M. Strässle 1, M. Huser 1,2, Ph. Jetzer 1,2 and F. De Paolis 3

1 Institut für Theoretische Physik der Universität Zürich, Winterthurer Strasse 190, CH-8057 Zürich, Switzerland
2 Paul Scherrer Institut, Laboratory for Astrophysics, CH-5232 Villigen PSI, Switzerland
3 Department of Physics and INFN, University of Lecce, CP 193, I-73100 Lecce, Italy

Received 25 January 1999 / Accepted 24 June 1999

Abstract

Dwarf galaxies are dominated by dark matter even in the innermost regions and, therefore, provide excellent probes for the investigation of dark halos. To that purpose, we analyse ROSAT PSPC-data of the dwarf galaxy NGC 247. We focus in particular on the diffuse X-ray emission in the [FORMULA]keV band. Assuming an isothermal density profile, we find that the mass of the hot emitting gas is about [FORMULA], corresponding to [FORMULA] of the total dynamical mass of the galaxy. The total mass of NGC 247, as derived from the X-ray data agrees quite well with the value obtained from the measured rotation curve (Burlak 1996).

The X-ray profile in the [FORMULA]keV and [FORMULA]keV band shows an excess at a radial distance of about [FORMULA] arcmin from the center. Such a "hump" in the radial X-ray profile can be explained by the presence of a cluster of young low mass stars or brown dwarfs. Therefore, NGC 247 offers the possibility to observe the formation of a halo of MACHOs.

Key words: galaxies: dwarf – galaxies: individual: NGC 247 – cosmology: dark matter – X-rays: galaxies

Send offprint requests to: marcus@physik.unizh.ch

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999
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