90 GHz Continuum Observations of Messier 66
arXiv:1205.1770 · doi:10.1111/j.1365-2966.2012.21517.x
Abstract
Radio emission at around 90 GHz from star-forming galaxies is expected to be strongly dominated by the free-free component due to ionising radiation from massive, short-lived, stars. We present high surface-brightness sensitivity observations at 90 GHz of the nearby star-forming galaxy Messier 66 with resolution of about 9 arcsec (corresponding to a physical scale of about 500 pc) and analyse these observations in combination with archival lower frequency radio and mid-infrared measurements. For the four regions for which the observations support our models we find that the free-free component indeed dominates the emission at 90 GHz, making up 76--90 per cent of the luminosity at this frequency but with the data also consistent with all of the emission being due to free-free. The estimates of free-free luminosities are also consistent, within measurement and decomposition errors, with star-formation rates derived from lower radio frequencies and mid-infrared observations. In our analysis we consider both power-law and curved spectra for the synchrotron component but do not find evidence to support the curved model in preference to the power-law.
7 pages, 5 figures. Submitted to MNRAS. Further information, plots, links to software are available at http://www.mrao.cam.ac.uk/~bn204/galevol/2012-90ghz-m66.html
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