An 850-micron SCUBA map of the Groth Strip and reliable source extraction

We present an 850-micron map and list of candidate sources in a 70 arcmin^2 sub-area of the Groth Strip observed using SCUBA. We initially detect 7 candidate sources with signal-to-noise ratios (SNRs) between 3.0 and 3.5 and 4 candidate sources with SNR > 3.5. Simulations suggest that on average in a map this size one expects 1.6 false positive sources for SNR > 3.5 and 4.5 for 3 < SNR < 3.5. Flux boosting in maps is a well known effect and we have developed a simple Bayesian prescription for estimating the unboosted flux distribution and used this method to determine the best flux estimates of our sources. This method is easily adapted for any other modest signal-to-noise survey in which there is prior knowledge of the source counts. We performed follow-up photometry in an attempt to confirm or reject 5 of our source candidates. We confirm the reality of 2 of the SCUBA sources, although at lower levels than suggested in the map and we find that the photometry results are consistent with and confirm the de-boosted map fluxes. Our final candidate source list contains 3 sources, including the 2 confirmed detections and 1 further candidate source with SNR > 3.5 which has a reasonable chance of being real.