OPTICAL IDENTIFICATIONS OF RADIO-SOURCES IN THE 5C 6 SURVEY

The general problem of optically identifying radio sources using the data available in 5C surveys is analysed in detail. Positions and finding charts are presented for candidate identifications of radio sources in the 5C 6 survey from deep plates taken with the Palomar 48-inch Schmidt telescope. At 1407 MHz, 26 out of 49 sources for which radio positions of accuracy ~ 1 arcsec are available are found to have candidate optical identifications; only three of these are expected to be due to chance. A much higher probability of making an identification for extended or flat-spectrum sources is found at this frequency than at 408 MHz. At 408 MHz the positional uncertainties are generally too large to obtain identifications of high reliability. For a sample of 20 bright sources (5(408) 500 mJy), about 30 per cent are identified. Overall, the identification percentage at 408 MHz for the remaining 243 sources in the survey is about 17 per cent for first nearest neighbours, once allowance is made for background contamination. © Royal Astronomical Society.