THE VLA-COSMOS PERSPECTIVE ON THE INFRARED-RADIO RELATION. I. NEW CONSTRAINTS ON SELECTION BIASES AND THE NON-EVOLUTION OF THE INFRARED/RADIO PROPERTIES OF STAR-FORMING AND ACTIVE GALACTIC NUCLEUS GALAXIES AT INTERMEDIATE AND HIGH REDSHIFT

VLA 1.4 GHz (sigma similar to 0.012 mJy) and MIPS 24 and 70 mu m (sigma similar to 0.02 and 1.7 mJy, respectively) observations covering the 2 deg(2) COSMOS field are combined with an extensive multiwavelength data set to study the evolution of the infrared (IR)-radio relation at intermediate and high redshift. With similar to 4500 sources-of which similar to 30% have spectroscopic redshifts-the current sample is significantly larger than previous ones used for the same purpose. Both monochromatic IR/radio flux ratios (q(24) and q(70)), as well as the ratio of the total IR and the 1.4 GHz luminosity (q(TIR)), are used as indicators for the IR/radio properties of star-forming galaxies and active galactic nuclei (AGNs). Using a sample jointly selected at IR and radio wavelengths in order to reduce selection biases, we provide firm support for previous findings that the IR-radio relation remains unchanged out to at least z similar to 1.4. Moreover, based on data from similar to 150 objects we also find that the local relation likely still holds at z is an element of [2.5, 5]. At redshift z < 1.4, we observe that radio-quiet AGNs populate the locus of the IR-radio relation in similar numbers as star-forming sources. In our analysis, we employ the methods of survival analysis in order to ensure a statistically sound treatment of flux limits arising from non-detections. We determine the observed shift in average IR/radio properties of IR- and radio-selected populations and show that it can reconcile apparently discrepant measurements presented in the literature. Finally, we also investigate variations of the IR/radio ratio with IR and radio luminosity and find that it hardly varies with IR luminosity but is a decreasing function of radio luminosity.