Mathematics – Probability
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...287..410u&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 287, no. 2, p. 410-418
Mathematics
Probability
5
Astronomical Models, Galactic Radio Waves, Helical Windings, Interstellar Magnetic Fields, Magnetic Field Configurations, Polarized Radiation, Radio Emission, Radio Observation, Spiral Galaxies, Azimuth, Far Infrared Radiation, Probability Theory, Radio Astronomy, Star Formation
Scientific paper
A model of the polarized radio emission from the spiral galaxy M 31, involving a mixture of random and compared with radio polarization observations. A model with a mixture of random and purely azimuthal fields is analyzed, too. The fraction of the helical (or azimuthal) field as well as the cosmic ray electron density are assumed to be functions of the star formation rate, the latter being measured by the far-infrared brightness. The model involving the helically twisted field is found to fit the observational data considerably better than that assuming only longitudinal and random field components. Best results are obtained for the field twisted at a pitch angle psi of about 30 deg. However, in this case an admixture of a random field is necessary. Most of the observed characteristics of M 31 are correctly reproduced if the total field strength is independent of azimuthal angle while the fraction of the helical field changes with azimuth as the square of the far-infrared brightness. The analysis of observational errors shows that the differences between the azimuthal model and observations are statistically significant. The probability of obtaining the observed characteristics of M 31 by random deviations from an azimuthal model is less than or equal to 1%. However, we consider only models obeying a simple functional relationship between the degree of the field uniformity and the star formation rate. We cannot at present reject the azimuthal models in which the ratio of uniform to random fields depends on other, yet unknown factors.
Beck Rainer
Otmianowska-Mazur Katarzyna
Urbanik Marek
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