The radio source population at high frequency: follow-up of the 15-GHz 9C survey

We have carried out extensive radio and optical follow-up of 176 sources from the 15GHz 9th Cambridge survey. Optical identifications have been found for 155 of the radio sources; optical images are given with radio maps overlaid. The continuum radio spectrum of each source spanning the frequency range 1.4 - 43GHz is also given. Two flux-limited samples are defined, one containing 124 sources complete to 25mJy and one of 70 sources complete to 60mJy. Between one fifth and one quarter of sources from these flux-limited samples display convex radio spectra, rising between 1.4 and 4.8GHz. These rising-spectrum sources make up a much larger fraction of the radio source population at this high selection frequency than in lower frequency surveys. We find that by using non-simultaneous survey flux density measurements at 1.4 and 15GHz to remove steep spectrum objects, the efficiency of s