We present maps, source catalogue and number counts of the largest, most complete and unbiased extragalactic submillimetre survey: the 850‐μm SCUBA Half‐Degree Extragalactic Survey (SHADES). Using the Submillimetre Common‐User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT), SHADES mapped two separate regions of sky: the Subaru/XMM–Newton Deep Field (SXDF) and the Lockman Hole East (LH). Encompassing 93 per cent of the overall acquired data (i.e. data taken up to 2004 February 1), these SCUBA maps cover 720 arcmin2 with a rms noise level of about 2 mJy and have uncovered >100 submillimetre galaxies. In order to ensure the utmost robustness of the resulting source catalogue, data reduction was independently carried out by four subgroups within the SHADES team, providing an unprecedented degree of reliability with respect to other SCUBA catalogues available from the literature. Individual source lists from the four groups were combined to produce a robust 120‐object SHADES catalogue; an invaluable resource for follow‐up campaigns aiming to study the properties of a complete and consistent sample of submillimetre galaxies. For the first time, we present deboosted flux densities for each submillimetre galaxy found in a large survey. Extensive simulations and tests were performed separately by each group in order to confirm the robustness of the source candidates and to evaluate the effects of false detections, completeness and flux density boosting. Corrections for these effects were then applied to the data to derive the submillimetre galaxy source counts. SHADES has a high enough number of detected sources that meaningful differential counts can be estimated, unlike most submillimetre surveys which have to consider integral counts. We present differential and integral source number counts and find that the differential counts are better fit with a broken power law or a Schechter function than with a single power law; the SHADES data alone significantly show that a break is required at several mJy, although the precise position of the break is not well constrained. We also find that a 850‐μm survey complete down to 2 mJy would resolve 20–30 per cent of the far‐infrared background into point sources.

Determining an accurate position for a submillimetre (submm) galaxy (SMG) is the crucial step that enables us to move from the basic properties of an SMG sample – source counts and 2D clustering – to an assessment of their detailed, multiwavelength properties, their contribution to the history of cosmic star formation and their links with present‐day galaxy populations. In this paper, we identify robust radio and/or infrared (IR) counterparts, and hence accurate positions, for over two‐thirds of the SCUBA HAlf‐Degree Extragalactic Survey (SHADES) Source Catalogue, presenting optical, 24‐μm and radio images of each SMG. Observed trends in identification rate have given no strong rationale for pruning the sample. Uncertainties in submm position are found to be consistent with theoretical expectations, with no evidence for significant additional sources of error. Employing the submm/radio redshift indicator, via a parametrization appropriate for radio‐identified SMGs with spectroscopic redshifts, yields a median redshift of 2.8 for the radio‐identified subset of SHADES, somewhat higher than the median spectroscopic redshift. We present a diagnostic colour–colour plot, exploiting Spitzer photometry, in which we identify regions commensurate with SMGs at very high redshift. Finally, we find that significantly more SMGs have multiple robust counterparts than would be expected by chance, indicative of physical associations. These multiple systems are most common amongst the brightest SMGs and are typically separated by 2–6 arcsec, at z∼ 2, consistent with early bursts seen in merger simulations.

We have analysed deep R‐band images, down to a limiting surface brightness of 26.5 R‐mag arcsec−2 (equivalent to ∼28 B‐mag arcsec−2), of five cD galaxies to determine the shape of the surface brightness profiles of their extended stellar envelopes. Both de Vaucouleurs R1/4 and Sérsic R1/n models, on their own, provide a poor description of the surface brightness profiles of cD galaxies. This is due to the presence of outer stellar envelopes, thought to have accumulated over the merger history of the central cluster galaxy and also from the tidal stripping of galaxies at larger cluster radii. We therefore simultaneously fit two Sérsic functions to measure the shape of the inner and outer components of the cD galaxies. We show that, for three out of our five galaxies, the surface brightness profiles are best fitted by an inner Sérsic model, with indices n∼ 1 –6, and an outer exponential component. For these systems, the galaxy‐to‐envelope size ratio is 0.1–0.4 and the contribution of the stellar envelope to the total R‐band light (i.e. galaxy + envelope) is around 60–80 per cent (based on extrapolation to a 300 kpc radius). The exceptions are NGC 6173, for which our surface brightness profile modelling is consistent with just a single component (i.e. no envelope) and NGC 4874 which appears to have an envelope with a de Vaucouleurs, rather than exponential, profile.

Abstract. We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lyα (DLA) absorption and low-and high-ionization lines at a redshift z = 3.3718 ± 0.0005. The inferred neutral hydrogen column density, log N(H i) = 21.90 ± 0.07, is larger than any (GRB-or QSO-) DLA H  column density inferred directly from Lyα in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: A V < 0.5 mag. The iron abundance is [Fe/H] = −1.47 ± 0.11, while the metallicity of the gas as measured from sulphur is [S/H] = −1.26 ± 0.20. We derive an upper limit on the H 2 molecular fraction of 2N(H 2 )/(2N(H 2 ) + N(H i)) < ∼ 10 −6 . In the Lyα trough, a Lyα emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 M yr −1 . All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, Si *, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the H  volume density to be n H i = 10 2 −10 4 cm −3 . HST/ACS imaging 4 months after the burst shows an extended AB(F606W) = 28.0 ± 0.3 mag object at a distance of 0. 14 (1 kpc) from the early afterglow location, which presumably is the host galaxy of GRB 030323.