We describe an observational program aimed at understanding the radio emission from distant , rapidly evolving galaxy populations .
These observations were carried out at 1.4 and 8.5 GHz with the VLA centered on the Hubble Deep Field , obtaining limiting flux densities of 40 and 8 \mu Jy respectively .
The differential count of the radio sources is marginally sub-Euclidean to the completeness limits ( \gamma = -2.4 \pm 0.1 ) and fluctuation analysis suggests nearly 60 sources per arcmin ^ { 2 } at the 1 \mu Jy level .
Using high resolution 1.4 GHz observations obtained with MERLIN , we resolve all radio sources detected in the VLA complete sample and measure a median angular size for the microjansky radio population of 1-2 ^ { \prime \prime } .
This clue coupled with the steep spectral index of the 1.4 GHz selected sample suggests diffuse synchrotron radiation in z \sim 1 galactic disks .

The wide-field HST and ground-based optical exposures show that the radio sources are identified primarily with disk systems composed of irregulars , peculiars , interacting/merging galaxies , and a few isolated field spirals .
Only 20 % of the radio sources can be attributed to AGN – the majority are likely associated with starburst activity .
The available redshifts range from 0.1-3 , with a mean of about 0.8 .
We are likely witnessing a major episode of starburst activity in these luminous ( L > L * ) systems , occasionally accompanied by an embedded AGN .

About 20 % of the radio sources remain unidentified to I = 26-28 in the HDF and flanking fields .
Several of these objects have extremely red counterparts .
We suggest that these are high redshift dusty protogalaxies .