Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981ap%26ss..79..419s&link_type=abstract
Astrophysics and Space Science, vol. 79, no. 2, Oct. 1981, p. 419-434.
Astronomy and Astrophysics
Astronomy
4
Brightness Distribution, Cosmic Rays, Density Distribution, Galactic Radio Waves, Gamma Ray Astronomy, Interstellar Gas, Magnetic Fields, Molecular Gases, Neutral Gases, Radio Observation, Sky Surveys (Astronomy)
Scientific paper
The longitudinal distribution of gamma rays from SAS-II data has been analyzed in order to derive consistent information on the possible variation of cosmic ray density over the Galaxy. Radio brightness distributions at 408 MHz were also used to deduce variations of the magnetic field. The observed density distributions of neutral and molecular gases, both in clouds and in an intercloud medium, were used; the density distribution of these components perpendicular to the galactic plane, and the variation of their scale-height in the outer parts of the Galaxy were also considered. The low intensity of cosmic rays observed near the central region of the Galaxy is explained by the assumption that the molecular gas in this region is in the form of dense cloudlets, which cannot be penetrated by low energy cosmic rays. An analysis of the radio sky survey at 408 MHz shows that the perpendicular magnetic-field component varies with a scale-length of about 40 kpc; no significance could be found in the apparent deviation from the equipartition of energy densities between cosmic rays and the magnetic field. The surface brightness of radio and gamma-ray emissions in the Galaxy decreases from the center with scale-lengths of about 6 and 7 kpc, respectively. No positive correlation can be found with either corotation radius or pattern speed, when compared with external spiral galaxies.
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