The molecular connection to the FIR-radio continuum correlation in galaxies

M. Murgia, T. T. Helfer, R. Ekers, L. Blitz, L. Moscadelli, T. Wong, R. Paladino

Research output: Contribution to journalArticlepeer-review


We have studied the relationships between the radio continuum (RC) and CO emission for a set of galaxies selected from the BIMA Survey of Nearby Galaxies. We find that the global CO-RC correlation is as tight as the global FIR-RC correlation for the 24 galaxies studied. Within 9 galaxies with ∼6″ CO and RC data available, the CO and RC emission is as tightly correlated as its global value; the radially averaged correlation is nearly linear, extends over four order of magnitude and holds down to the smallest linear resolution of the observations, which is ∼100 pc. We define qCO/RC as the log of the ratio of the CO to RC flux as a way to characterize the CO-RC correlation. Combining 6″ pixel-by-pixel comparisons across all sources yields an average small-scale correlation of qCO/RC = 1.1±0.28; that is, the spatially resolved correlation has a dispersion that is less than a factor of 2. There are however systematic variations in the CO/RC ratio; the strongest organized structures in qCO/RC tend to be found along spiral arms and on size scales much larger than the resolution of the observations. We do not measure any systematic trend in CO/RC ratio as a function of radius in galaxies. The constancy of the CO/RC ratio stands in contrast to the previously measured decrease in the FIR/RC ratio as a function of radius in galaxies. We suggest that the excellent correlation between the CO, RC and FIR emission in galaxies is a consequence of regulation by hydrostatic pressure; this model links all three emissions without invoking an explicit dependence on a star formation scenario.

Original languageEnglish (US)
Pages (from-to)389-410
Number of pages22
JournalAstronomy and Astrophysics
Issue number2
StatePublished - Jul 2005
Externally publishedYes


  • Galaxies: spiral
  • ISM: molecules
  • Radio continuum: galaxies
  • Stars: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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