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T.T. Helfer (Radio Astronomy Lab, UC Berkeley), M. Murgia (Instituto di Radioastronomia del CNR), R.D. Ekers (ATNF/CSIRO), L. Blitz (RAL, UCB), T. Wong (ATNF/CSIRO), L. Moscadelli (Osservatorio Astronomico di Cagliari), L. Gregorini (Instituto di Radioastronomia del CNR)
The well-known correlation between global radio continuum (RC) and far-infrared (FIR) emissions in external galaxies is at the same time one of the most robust and one of the most puzzling relations in extragalactic astronomy. The RC/FIR correlation is linear and has a dispersion of only a factor of two, over a luminosity range of more than four orders of magnitude (e.g. Condon 1992, ARAA, 30, 576; Yun, Reddy, & Condon 2001, 554, 803). The RC/FIR relation appears to hold within galaxies down to size scales of about 100 pc, but breaks down on smaller scales (B. Wells, PhD thesis). Even though the RC and FIR are both thought ultimately to originate as a result of star formation in molecular clouds, the tightness of the correlation is surprising given the many disparate steps involved in producing the two types of emission: the FIR is generally believed to originate from warm dust that is heated by the radiation from hot young stars, and the RC originates as synchrotron emission from relativistic electrons accelerated by supernova remnants. In this paper, we explore the molecular cloud links to the FIR and RC in about a dozen sources by using the new, 6"-resolution CO data from the BIMA Survey of Nearby Galaxies (SONG). We also examine these correlations on global scales for two dozen galaxies. Preliminary results show that within some sources, the CO and RC emissions are linearly correlated to within the errors in the flux density measurements. Within other galaxies, the small-scale correlation may be somewhat less precise, at least on size scales as small as a few hundred parsecs.
This research is supported in part by NSF grant AST 99-81308.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.