Mathematics – Logic
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21330706m&link_type=abstract
American Astronomical Society, AAS Meeting #213, #307.06; Bulletin of the American Astronomical Society, Vol. 41, p.278
Mathematics
Logic
Scientific paper
We compare the gaseous and relativistic phases of the interstellar medium (ISM) within nearby star-forming galaxies using far-infrared (FIR) and radio continuum imagery obtained as part of the Spitzer Infrared Nearby Galaxies Survey.
We find that the dispersion in the FIR/radio ratios within galaxies on sub-kpc scales is similar to that found among galaxies. By comparing the residual dispersion around FIR/radio ratios with other physically motivated parameters we conclude that the FIR-radio correlation is most sensitive to star formation activity. We also find that the dispersion in the FIR/radio ratios within galaxies is significantly reduced using a phenomenological image-smearing model; the infrared images are convolved with a parameterized kernel to approximate the time-dependent diffusion of cosmic-ray (CR) electrons and thus reproduce the general appearance of the radio images.
Using this technique we have characterized the diffusion of CR-electrons in galaxies other than the Milky Way and find that the mean distance traveled by CR-electrons is most sensitive to the dominant age of the CR-electron population, rather than ISM parameters which may inhibit their propagation such as density, radiation-field energy density, and magnetic-field strength. We also find that the global CR-electron population transitions from being dominated by old to recently accelerated CR-electrons with increasing star formation intensity. Irregular galaxies do not fit this phenomenology, likely due to enhanced CR-electron escape.
By comparing FIR/radio ratios within cluster galaxies to those in the field we find systematic differences. Since their FIR disks appear symmetric, we apply our image-smearing analysis to create model radio continuum images for comparison with the observed radio data. We find radio deficit regions along edges thought to be experiencing intracluster medium (ICM)-ISM pressure. We propose that the ICM wind has swept up the low density relativistic ISM and created shocks that have re-accelerated CR-electrons and sheared the magnetic field.
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