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Université Paul Sabatier - Toulouse III (24/11/1997), Peter von Ballmoos (Dir.)

The origin of 26Al in the Galaxy

Jürgen Knödlseder 1

(24/11/1997)

The history of recent galactic nucleosynthesis activity can be studied by measurements of the 1.809 MeV gamma-ray line arising from the decay of radioactive 26Al. The COMPTEL telescope aboard the Compton Gamma-Ray Observatory, launched on April 5, 1991, permits for the first time an extensive investigation of the 1.8 MeV radiation throughout the entire sky. The aim of this thesis is to infer the galactic distribution of 26Al from these measurements and to identify the dominant sources of this radioactive isotope. The first part of the thesis is dedicated to the reconstruction of the 1.8 MeV intensity distribution from the measured data. It is demonstrated that the use of conventional deconvolution algorithms, like maximum likelihood or maximum entropy inversion, leads to lumpy, noise-dominated intensity distributions. Nevertheless, simulations can help to assess the uncertainties in the reconstructed images, which permits the scientific exploitation of the recovered skymaps. Alternatively, a multiresolution approach is proposed, which largely reduces the uncertainties in the reconstructed 1.8 MeV intensity distribution. In summary, 1.8 MeV emission is mainly concentrated towards the galactic plane, which clearly demonstrates that the bulk of 26Al is of galactic rather than local origin. However, distinct emission features towards Cygnus, Carina, and the Auriga-Camelopardalis-Perseus region are inconsistent with a smooth galactic 1.8 MeV emission profile, pointing towards a massive star origin of 26Al. The second part of the thesis consists of a multi-wavelength comparison of COMPTEL 1.8 MeV data which aims in the identification of the origin of galactic 26Al. For the comparison, a rigorous Bayesian analysis is applied, which is the only consistent framework that allows inference based on the comparison. It turned out that the 1.8 MeV distribution follows very closely the distribution of free electrons in the Galaxy which is traced by thermal bremsstrahlung, observable in the microwave domain. The similarity of the 1.8 MeV intensity distribution to the thermal bremsstrahlung distribution implies a direct proportionality between the 26Al and the massive star column densities, which strongly supports that massive stars are the origin of galactic 26Al. In particular, ONeMg-novae and AGB stars can be excluded as dominant 26Al sources since their galactic distribution is not expected to correlate with the distribution of free electrons. The correlation between 26Al and free electrons established, the analysis of 1.8 MeV gamma-ray line emission can complement our knowledge about star formation and the distribution of ionized gas throughout the entire Galaxy. While COMPTEL made the first step in providing the first all-sky map in the light of the 1.809 MeV line, INTEGRAL, the next generation gamma-ray spectrometer, will allow a detailed study of current star formation in the Galaxy.

1 :	Centre d'étude spatiale des rayonnements (CESR)
	CNRS : UMR5187 – Observatoire Midi-Pyrénées – INSU – Université Paul Sabatier [UPS] - Toulouse III

domaine

:

Planète et Univers/Astrophysique Physique/Physique Nucléaire Théorique Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

mots-clés : gamma-ray astronomy – radioactivity – massive stars

tel-00145359, version 1

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Contributeur : Jürgen Knödlseder <>

Soumis le : Mercredi 9 Mai 2007, 18:21:41

Dernière modification le : Mercredi 9 Mai 2007, 23:17:02