Radio Emission from Galaxies in the Hubble Deep Field

We report on sensitive radio observations made with the VLA at 8.5 GHz,centered on the Hubble Deep Field (HDF). We collected data in the A, CnB, C,DnC, and D configurations, corresponding to angular resolutions ranging from0.3" to 10". We detected 29 radio sources in a complete sample within 4.6' ofthe HDF center and above a flux density limit of 9.0 microjy (5 sigma). Sevenof these sources are located within the HDF itself, while the remaining 22sources are covered by the Hubble Flanking Fields (HFFs) or ground basedoptical images. All of the sources in the HDF are identified with galaxies witha mean magnitude R = 21.7, while the mean magnitude of the identificationsoutside the HDF is R = 22.1. Three radio sources have no optical counterpartsto R = 27. Based on a radio and optical positional coincidence, we detected anadditional 19 radio sources in this field (seven of which are contained in theHDF) with 6.3 microjy < S < 9.0 (3.5 sigma < S < 5 sigma) and and R < 25, butwhich are not included in the complete sample. At least 2/3 of the optical identifications of these microjansky radiosources are with disk systems (i.e., irregulars, mergers and spirals). Webriefly discuss the possible physical mechnisms driving the strong evolution inthe microjansky radio galaxy population. [truncated]