We investigate the multi-wavelength emission of BzK selected star forming galaxies at z \sim 2 in the Great Observatories Origins Deep Survey ( GOODS ) North region .
Most ( 82 % ) of the sources are individually detected at 24 \mu m in the Spitzer MIPS imaging , and one fourth ( 26 % ) in the VLA radio data .
Significant detections of the individually undetected objects are obtained through stacking in the radio , submm and X-ray domains .
The typical star forming galaxy with stellar mass \sim 10 ^ { 11 } M _ { \odot } at z = 2 is an Ultra-luminous Infrared Galaxy ( ULIRG ) , with L _ { IR } \sim 1 –2 \times 10 ^ { 12 } L _ { \odot } and star formation rate SFR \approx 200 –300 M _ { \odot } yr ^ { -1 } , implying a comoving density of ULIRGs at z = 2 at least 3 orders of magnitude above the local one . SFR s derived from the reddening corrected UV luminosities agree well , on average , with the longer wavelength estimates .
The high 24 \mu m detection rate suggests a relatively large duty cycle for the BzK star forming phase , consistently with the available independent measurements of the space density of passively evolving galaxies at z > 1.4 .
If the IMF at z = 2 is similar to the local one , and in particular is not a top-heavy IMF , this suggests that a substantial fraction of the high mass tail ( \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 10 ^ { 11 } M _ { \odot } ) of the galaxy stellar mass function was completed by z \approx 1.4 .