e-MERLIN observations at 5 GHz of the GOODS-N region: pinpointing AGN cores in high-redshift galaxies

We present 5 GHz e-Multi-Element Radio-Linked Interferometer Network (e-MERLIN) observations of the Great Observatories Origins Deep Surveys North (GOODS)-N region at sub-arcsec resolution (0.2-0.5 arcsec). These data form part of the early commissioning observations for the e-MERLIN interferometer and a pilot for the e-MERLIN legacy programme e-MERLIN Galaxy Evolution Survey (eMERGE). A total of 17 sources were detected with S/N > 3. These observations provide unique information on the radio source morphology at sub-arcsec scales. For twelve of these sources, deeper 1.4 GHz MERLIN+Very Large Array observations at the same spatial resolution are available, allowing radio spectral indices to be derived for 10 sources on sub-arcsec angular scales. Via analysis of the spectral indices and radio morphologies, these sources have been identified as active galactic nucleus (AGN) cores in moderate-to-high-redshift (1 <z <4) galaxies. These results have provided AGN (or AGN-candidate) classification for six previously unclassified sources and confirmed the AGN nature of the rest of the sample. Ultimately, the eMERGE project will image the GOODS-N region at 1.4 and 5 GHz with higher resolution (about 50 mas at 5 GHz) and down to sub-μJy sensitivities. The unique combination of sensitivity and spatial resolution will be exploited to study star formation and AGN activity in distant galaxies.