Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...345..674k&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 345, Oct. 15, 1989, p. 674-696.
Astronomy and Astrophysics
Astrophysics
38
Galactic Structure, H Ii Regions, Interstellar Matter, Spiral Galaxies, Astronomical Maps, Astronomical Photometry, Density Wave Model, Gray Scale, Radio Emission, Resonance, Shock Fronts
Scientific paper
High-resolution digitized images of M81 in H I, B and I bands, H-alpha, and the radio continuum are studied. The H I gas, the nonthermal radio emission, the dust and the narrow dust filaments, the young stars, and the giant radio H II regions are each distributed across a broad spiral compression zone that starts near the measured position of the spiral velocity shock front and extends 1-2 kpc downstream from the shock front. Old and young stars both collect near the gravitational potential minimum on the arms. The evidence favors an SNR origin for the cosmic ray electrons that produce the nonthermal radio arms. The location of an H II region above or below the midplane explains the observed dispersion in the value of the visual extinction for the set of giant radio H II regions. Many of the general features of the spiral arms can be explained by density wave models that emphasize the cloudy nature of the interstellar medium.
Bash Frank N.
Elmegreen Debra Meloy
Hine Butler
Hodge Paul W.
Kaufman Michele
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