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Astron. Astrophys. 350, L9-L12 (1999)

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Letter to the Editor

H2 dark matter in the galactic halo from EGRET

P.M.W. Kalberla 1, Yu.A. Shchekinov 2,3 and R.-J. Dettmar 4

1 Universität Bonn, Radioastronomisches Institut, D-53121 Bonn, Germany
2 Rostov State University, Department of Physics, 344090 Rostov on Don, Russia
3 Osservatorio Astrofisico di Arcetri, I-50125 Florence, Italy
4 Ruhr-Universität Bochum, Astronomisches Institut, D-44780 Bochum, Germany

Received 8 July 1999 / Accepted 2 September 1999


We present a model for the interpretation of the [FORMULA]-ray background emission from the Galactic halo, which we attribute to interaction of high-energy cosmic rays with dense molecular clumps. In a wide range of clump parameters we calculate the expected [FORMULA]-photon flux, taking into account for the first time optical depth effects. This allows us to derive new constraints on masses and sizes of possible molecular clumps and their contribution to the galactic surface density.

The observed [FORMULA]-ray distribution can be explained best by models with a flattened halo distribution of axis ratio [FORMULA]. If optical depth effects are important, the clumps must have radii of [FORMULA] AU and masses of [FORMULA]. This would result in a total mass of [FORMULA] for such clumps and contribute with [FORMULA] to the local surface density.

Key words: Galaxy: halo – gamma rays: observations – cosmology: dark matter

This article contains no SIMBAD objects.


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© European Southern Observatory (ESO) 1999

Online publication: September 24, 1999