NO EVOLUTION IN THE IR-RADIO RELATION FOR IR-LUMINOUS GALAXIES AT z < 2 IN THE COSMOS FIELD

Previous observational studies of the infrared (IR)-radio relation out to high redshift employed any detectable star-forming systems at a given redshift within the restricted area of cosmological survey fields. Consequently, the evolution inferred relies on a comparison between the average IR/radio properties of (1) very IR-luminous high-z sources and (2) more heterogeneous low(er)-z samples that often lack the strongest IR emitters. In this Letter, we consider populations of objects with comparable luminosities over the last 10 Gyr by taking advantage of deep IR (especially Spitzer 24 μm) and Very Large Array 1.4 GHz observations of the COSMOS field. Consistent with recent model predictions, both Ultra Luminous Infrared Galaxies and galaxies on the bright end of the evolving IR luminosity function do not display any change in their average IR/radio ratios out to z ∼ 2 when corrected for bias. Uncorrected data suggested ∼0.3 dex of positive evolution.