The SCUBA half-degree extragalactic survey - I. Survey motivation, design and data processing

The Submillimetre Common-User Bolometer Array ( SCUBA) Half-Degree Extragalactic Survey ( SHADES) is a major new blank-field extragalactic submillimetre (submm) survey currently underway at the James Clerk Maxwell Telescope (JCMT). Ultimately, SHADES aims to cover half a square degree at 450 and 850 mu m to a 4 sigma depth of similar or equal to 8 mJy at 850 mu m. Two fields are being observed, the Subaru/XMM-Newton Deep Field (SXDF) (02(h)18(m) - 05 degrees.) and the Lockman Hole East (10(h)52(m) + 57 degrees). The survey has three main aims: (i) to investigate the population of high-redshift submm galaxies and the cosmic history of massive dust-enshrouded star formation activity; (ii) to investigate the clustering properties of submm-selected galaxies in order to determine whether these objects could be progenitors of present-day massive ellipticals; and (iii) to investigate the fraction of submm-selected sources that harbour active galactic nuclei. To achieve these aims requires that the submm data be combined with cospatial information spanning the radio-to-X-ray frequency range. Accordingly, SHADES has been designed to benefit from ultra-deep radio imaging obtained with the Very Large Array (VLA), deep mid-infrared observations from the Spitzer Space Telescope, submm mapping by the Balloon-borne Large Aperture Submillimetre Telescope ( BLAST), deep near-infrared imaging with the United Kingdom Infrared Telescope, deep optical imaging with the Subaru Telescope and deep X-ray observations with the XMM-Newton observatory. It is expected that the resulting extensive multiwavelength data set will provide complete photometric redshift information accurate to delta(z) <= 0.5 as well as detailed spectral energy distributions for the vast majority of the submm-selected sources. In this paper, the first of a series on SHADES, we present an overview of the motivation for the survey, describe the SHADES survey strategy, provide a detailed description of the primary data-analysis pipeline and demonstrate the superiority of our adopted matched-filter source-extraction technique over, for example, Emerson-II style methods. We also report on the progress of the survey. As of 2004 February, 720 arcmin(2) had been mapped with SCUBA ( about 40 per cent of the anticipated final total area) to a median 1 sigma depth of 2.2 mJy per beam at 850 mu m (25 mJy per beam at 450 mu m), and the source-extraction routines give a source density of 650 +/- 50 sources de(g-)2 > 3 sigma at 850 mu m. Although uncorrected for Eddington bias, this source density is more than sufficient for providing enough sources to answer the science goals of SHADES, once half a square degree is observed. A refined reanalysis of the original 8-mJy survey Lockman hole data was carried out in order to evaluate the new data-reduction pipeline. Of the 17 most secure sources in the original sample, 12 have been reconfirmed, including 10 of the 11 for which radio identifications were previously secured.