The Microjansky Sky at 8.4 GH[CLC]z[/CLC]

We present the results from two radio integrations at 8.4 GHz using the VLA.One of the fields, at 13h,+43d (SA13 field), has an rms noise level of 1.49microJy and is the deepest radio image yet made. Thirty-four sources in acomplete sample were detected above 7.5 microJy and 25 are optically identifiedto a limit of I=25.8, using our deep HST and ground-based images. The radiosources are usually located within 0.5" (typically 5 kpc) of a galaxy nucleus,and generally have a diameter less than 2.5". The second field at 17h, +50d(Hercules Field) has an rms noise of 35 microJy and contains 10 sources. Wehave also analyzed a complete flux density-limited sample at 8.4 GHz of 89sources from five deep radio surveys, including the Hubble deep field. Half ofall the optical counterparts are with galaxies brighter than I=23 mag, but 20%are fainter than I=25.5 mag. We confirm the tendency for the micro-Jansky radiosources to prefer multi-galaxy systems. The distribution of the radio spectralindex between 1.4 and 8.4 GHz peaks at alpha = -0.75~ with a median value of-0.6. The average spectral index becomes steeper (lower values) for sourcesbelow 35 microJy, and for sources identified with optical counterparts fainterthan I=25.5 mag. The differential radio count between 7.5 and 1000 microJy hasa slope of -2.11 +/-0.13 and a surface density of 0.64 sources persquare-arcmin with flux density greater than $7.5 microJy.Comment: 21 pages, 8 figure