Speaker: Volker Heesen, University of Southhampton
Abstract: Radio continuum (RC) emission holds the promise of being an accurate because unobscured tracer for star formation (SF), allowing us to measure the evolution of the Cosmic star formation rate (SFR) in dusty high-z galaxies. We use WSRT RC observations at 22 cm and state-of-the-art hybrid SFR density maps, combining GALEX FUV data, tracing un-obscured SF, and Spitzer 24 mu data, tracing SF embedded in dust. With these data we calibrate the well-known RC-SFR relation as proposed by Condon (1992) on a spatially resolved basis in a sample of 17 nearby galaxies. We find that for integrated measurements Condon's relation works quite well: the absolute value of the RC derived SFR is in agreement with the hybrid SFR, and the RC-SFR relation is almost linear with RC ~ SFRD^(1.11pm0.05). The same holds true for azimuthally averaged data, where the ratio of RC to hybrid derived SFR density is almost constant with only quasi-periodic fluctuations of 25% amplitude. The spatially resolved data, however, shows that on a 1 kpc scale the RC-SFR relation is sub-linear, which we attribute largely to the effect of cosmic-ray transport. We study the dependence of the RC-SFR relation on various galaxy parameters and find none, meaning that the RC-SFR relation is universal.