Galaxy populations and redshift dependence of the correlation between infrared and radio luminosity

TL;DR

This study investigates how the infrared-radio luminosity ratio varies with redshift across different galaxy types, revealing consistent mean values and potential effects of cosmic microwave background interactions at high redshift.

Contribution

It introduces a model classifying galaxies into three types based on stellar age and analyzes their infrared-radio correlation across redshifts, highlighting physical condition differences.

Findings

Mean q_IR remains nearly constant across redshifts for each galaxy type.

Possible upturn of q_IR at z > 3.5 due to inverse Compton cooling effects.

Stellar mass differences explain the dependence of q_IR on galaxy populations.

Abstract

We argue that the difference in infrared-to-radio luminosity ratio between local and high-redshift star-forming galaxies reflects {the alternative physical conditions} -- including magnetic field configurations -- of the dominant population of star-forming galaxies in different redshift ranges. We define three galactic types, based on our reference model, with reference to ages of stellar populations. ``Normal'' late-type galaxies dominate the star formation in the nearby Universe; ``starburst'' galaxies take over at higher redshifts, up to z ~1.5; while ``protospheroidal'' galaxies dominate at high redshift. A reanalysis of data from the COSMOS field combined with literature results shows that, for each population, the data are consistent with an almost redshift-independent mean value of the parameter q_IR, which quantifies the infrared-radio correlation. However, we find a hint of an upturn of the mean q_IR at z>~3.5 consistent with the predicted dimming of synchrotron emission due to cooling of relativistic electrons by inverse Compton scattering off the cosmic microwave background. The typical stellar masses increase from normal, to starburst, and to protospheroidal galaxies, accounting for the reported dependence of the mean q_IR on stellar mass. Higher values of q_IR found for high-z strongly lensed dusty galaxies selected at 500 micron might be explained by differential magnification.