Mathematics – Probability
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.263...93b&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 263, no. 1, p. 93-97.
Mathematics
Probability
7
Disk Galaxies, Far Infrared Radiation, Interstellar Chemistry, Molecular Clouds, Radio Emission, Cosmic Rays, Gas Ionization, Interstellar Magnetic Fields
Scientific paper
We propose that the strong correlation between FIR emission and nonthermal radio emission in diverse types of disk galaxies arises because of differences in the chemical evolution of molecular clouds in these galaxies. The chemistry is driven by the cosmic ray flux, which is believed to produce the observed non-thermal emission. The chemical link with the IR flux is connected with the onset of the ion destruction era of the molecular cloud. Once the ion destruction era has been reached, the magnetic field is no longer 'frozen in', and so diffusion begins to take place. The greater the cosmic ray ionization rate, the greater the fractional ionization, as dictated by the chemistry. A cloud with a high degree of ionization persists longer because the time taken for the magnetic flux to leak from the cloud is longer, allowing more mass accretion along the field. The more massive clumps so formed are believed to have a greater probability of forming more massive OB stars, and hence enhance the interstellar UV flux and, via dust absorption and heating, produce more IR emission. Our hypothesis, together with the Monash model of molecular cloud chemistry, leads to predictions that the relative abundances of various interstellar molecules such as methanol, HCN, and formaldehyde will be correlated with the nonthermal radio emission.
Bettens Ryan P. A.
Brown Ronald D.
Cragg Dinah M.
Dickinson Clive J.
Godfrey Peter D.
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