The far-infrared/radio correlation for a sample of strongly lensed dusty star-forming galaxies detected by Herschel

We investigate the radio/far-infrared (FIR) correlation for a sample of 28 bright high-redshift (1 less than or similar to z less than or similar to 4) star-forming galaxies selected in the FIR from the Herschel ATLAS fields as candidates to be strongly gravitationally lensed. The radio information comes either from high sensitivity dedicated Australia Telescope Compact Array observations at 2.1 GHz or from cross-matches with the FIRST survey at 1.4 GHz. By taking advantage of source brightness possibly enhanced by lensing magnification, we identify a weak evolution with redshift out to z less than or similar to 4 of the HR-to-radio luminosity ratio q(FIR). We also find that the q(FIR) parameter as a function of the radio power L-1.4GHz displays a clear decreasing trend, similarly to what is observed for optically/radio-selected lensed quasars found in literature, yet covering a complementary region in the q(FIR)-L(1.4GHz )diagram. We interpret such a behaviour in the framework of an in situ galaxy formation scenario, as a result of the transition from an early dust-obscured star-forming phase (mainly pinpointed by our FIR selection) to a late radio-loud quasar phase (preferentially sampled by the optical/radio selection).