[40.03] Statistical and Physical Factors that Influence the Correlation Between Far-Infrared and Radio Continuum Emission in Galaxies

AAS 200th meeting, Albuquerque, NM, June 2002
Session 40. Evolution of Galaxies, Galaxy Surveys, IGM
Display, Tuesday, June 4, 2002, 10:00am-6:30pm, SW Exhibit Hall

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[40.03] Statistical and Physical Factors that Influence the Correlation Between Far-Infrared and Radio Continuum Emission in Galaxies

J. Mazzarella (Caltech, IPAC), S. Lefranc (IfA, U. Hawaii), B. Madore (Caltech, IPAC & OCIW), G. Helou (Caltech, IPAC/SSC)

Results are presented from a study aimed toward an improved understanding of factors that influence the well known relationship between the far-infrared (FIR) and radio continuum emission from galaxies. This work is based on data from various catalogs and journal articles as fused in the NASA/IPAC Extragalactic Database (NED), augmented by new direct measurements from the IRAS scan archive and NVSS images to account for emission from extended sources. The sample contains over 1000 objects.

The tight correlation between FIR and radio continuum luminosities often discussed in the literature is dominated by the strong dependency on the squared distance implicit in both parameters. Although the correlation between FIR and radio flux densities is real, it has a much lower correlation coefficient than in the luminosity-luminosity plane. Spurious luminosity correlations are easily produced using randomly paired FIR and radio flux densities that are uncorrelated. Apparent parallel correlations among radio-loud AGNs and normal star-forming galaxies in the log L_radio vs. log L_FIR plane (e.g., Sopp & Alexander 1991) are an artifact of the squared distance folded into each variable. The radio-loud AGNs do not correlate well in the log f_radio vs. log f_FIR plane, and their FIR/radio flux ratios quantify the degree of excess radio emission compared to normal galaxies. The FIR-radio flux correlation has a dependency on the integrated FIR color temperature of the galaxies: galaxies with warmer global dust temperatures have on average higher ratios of FIR-to-radio flux than galaxies with lower dust temperatures. Large deviations from the canonical FIR-radio flux correlation can usually be attributed to enhanced radio continuum emission from AGNs fueled by tidal interactions and mergers. These results and others are discussed in relation to previously published work on this subject.

This research is funded by NASA.

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