High-z radio starbursts host obscured X-ray AGN
  We use Virtual Observatory methods to investigate the association between radio and X-ray emission at high redshifts. Fifty-five of the 92 HDF(N) sources resolved by combining   MERLIN+VLA data were detected by Chandra, of which 18 are hard enough and bright enough to be obscured AGN. The high-z population of microJy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at z<1 and at least a quarter of these simultaneously host highly X-ray-luminous obscured AGN. 
A. M. S. Richards, R. J. Beswick, S. T. Garrington, T. W. B. Muxlow,   H. Thrall (Jodrell Bank Observatory), M. A. Garrett, ...