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 from 0.″3 to 10″. We detected 29 radio sources in a complete sample within 4.′6 of the HDF center and above a flux density limit of 9.0 μJy (5 σ). Seven of these sources are located within the HDF itself, while the remaining 22 sources are covered by the Hubble flanking fields (HFFs) or ground-based optical images. All of the sources in the HDF are identified with galaxies with a mean magnitude R = 21.7, while the mean magnitude of the identifications outside the HDF is R = 22.1. One radio source in the HDF, which is just below our formal completeness level but is confirmed by independent 1.4 GHz observations, has no optical counterpart above the HDF limit of R = 29. Three radio sources outside the HDF have no optical counterparts to R = 27. Based on a radio and optical positional coincidence, we detected an additional 19 radio sources in this field (seven of which are contained in the HDF) with 6.3 μJy ≤Sν < 9.0 μJy (3.5 σ ≤ Sν < 5 σ) and R ≤ 25 but which are not included in the complete sample. The microjansky radio sources are distributed over a wide range of redshifts (0.1 < z < 3) and have a typical monochromatic luminosity of about 1023 W Hz-1. The majority of the optical identifications are with luminous (L > L*) galaxies at modest redshifts (0 ≲ z ≲ 1), many with evidence for recent star formation. The remainder are composed of a mixture of bright field elliptical galaxies and late-type galaxies with evidence of nuclear activity (LINERs and Seyfert galaxies) and nearby (z < 0.2) field spiral galaxies. None of the radio sources in this survey are identified with quasars or galactic stars.