This paper is the second in a series describing the Sydney University Molonglo Sky Survey (SUMSS) being carried out at 843 MHz with the Molonglo Observatory Synthesis Telescope (MOST). The survey will consist of ∼590 4.3°× 4.3° mosaic images with 45 × 45 cosec|δ| arcsec2 resolution, and a source catalogue. In this paper we describe the initial release (version 1.0) of the source catalogue consisting of 107 765 radio sources made by fitting elliptical Gaussians in 271 SUMSS 4.3°× 4.3° mosaics to a limiting peak brightness of 6 mJy beam−1 at δ≤−50° and 10 mJy beam−1 at δ > −50°. The catalogue covers approximately 3500 deg2 of the southern sky with δ≤−30°, about 43 per cent of the total survey area. Positions in the catalogue are accurate to within 1–2 arcsec for sources with peak brightness A843≥ 20 mJy beam−1 and are always better than 10 arcsec. The internal flux density scale is accurate to within 3 per cent. Image artefacts have been classified using a decision tree, which correctly identifies and rejects spurious sources in over 96 per cent of cases. Analysis of the catalogue shows that it is highly uniform and is complete to 8 mJy at δ≤−50° and 18 mJy at δ > −50°. In this release of the catalogue about 7000 sources are found in the overlap region with the National Radio Astronomy Observatories Very Large Array Sky Survey at 1.4 GHz. We calculate a median spectral index of α=−0.83 between 1.4 GHz and 843 MHz. This version of the catalogue will be released via the World Wide Web with future updates as new mosaics are released.

Deep HST/ACS and VLT/ISAAC data of the GOODS-South field were used to look for high-redshift galaxies in the rest-frame UV wavelength range and to study the evolution of the cosmic star-formation density at z ∼ 7. The GOODS-South area was surveyed down to a limiting magnitude of about (J + Ks) AB = 25.5, looking for drop-out objects in the z 850 ACS filter. The large sampled area would allow for the detection of galaxies that are 20 times less numerous and 1-2 mag brighter than similar studies using HST/NICMOS near-IR data. Two objects had initially been selected as promising candidates for galaxies at z ∼ 7, but were subsequently dismissed and identified as Galactic brown dwarfs through detailed analysis of their morphology and Spitzer colors, as well as through spectroscopic information. As a consequence, we conclude that there are no galaxies at z ∼ 7 down to our limiting magnitude in the field we investigated. Our non detection of galaxies at z ∼ 7 provides clear evidence for a strong evolution of the luminosity function between z = 6 and z = 7, i.e. over a time interval of only ∼170 Myr. Our constraints also provide evidence of a significant decline in the total star formation rate at z = 7, which must be less than 40% of that at z = 3 and 40-80% of that at z = 6. We also derive an upper limit to the ionizing flux at z = 7, which is only marginally consistent with what is required to completely ionize the Universe.

Aims. The formation and evolution of cosmic structures can be probed by studying the evolution of the luminosity function of the Active Galactic Nuclei (AGNs), galaxies and clusters of galaxies and of the clustering of the X-ray active Universe, compared to the IR-UV active Universe. Methods. To this purpose, we have surveyed with XMM-Newton the central ∼0.6 deg 2 region of the ELAIS-S1 field down to flux limits of ∼5.5 × 10 −16 erg cm −2 s −1 (0.5-2 keV, soft band, S), ∼2 × 10 −15 erg cm −2 s −1 (2-10 keV, hard band, H), and ∼4 × 10 −15 erg cm −2 s −1 (5-10 keV, ultra hard band, HH). We present here the analysis of the XMM-Newton observations, the number counts in different energy bands and the clustering properties of the X-ray sources. Results. We detect a total of 478 sources, 395 and 205 of which detected in the S and H bands respectively. We identified 7 clearly extended sources and estimated their redshift through X-ray spectral fits with thermal models. In four cases the redshift is consistent with z = 0.4, so we may have detected a large scale structure formed by groups and clusters of galaxies through their hot intra-cluster gas emission. We have computed the angular correlation function of the sources in the S and H bands finding best fit correlation angles θ 0 = 5.2 ± 3.8 arcsec and θ 0 = 12.8 ± 7.8 arcsec in the two bands respectively. The correlation angle of H band sources is therefore formally ∼2.5 times that of the S band sources, although the difference is at only ∼1σ confidence level. A rough estimate of the present-day correlation length r 0 can be obtained inverting the Limber equation and assuming an appropriate redshift distribution dN/dz. The results range between 12.8 and 9.8 h −1 Mpc in the S band and between 17.9 and 13.4 h −1 Mpc in the H band, with 30-40% statistical errors, assuming either smooth redshift distributions or redshift distributions with spikes accounting for the presence of significant structure at z = 0.4. The relative density of the S band sources is higher near the clusters and groups at z ∼ 0.4 and extends toward East and toward South/West. This suggests that the structure is complex, with a size comparable to the full XMM-Newton field. Conversely, the highest relative source densities of the H band sources are located in the central-west region of the field.

Context. The ESO-Spitzer extragalactic Imaging Survey (ESIS) is the optical follow up of the Spitzer Wide-Area InfraRedExtragalactic (SWIRE) survey in the ELAIS-S1 area. Aims. The multiwavelength study of galaxy emission is the key to understand the interplay of the various components of galaxies and to trace their role in cosmic evolution. ESIS provides optical identification and colors of Spitzer IR galaxies and builds the bases for photometric redshift estimates. Methods. This paper presents B, V, R Wide Field Imager observations of the first 1.5 square degree of the ESIS survey. Data reduction is described including astrometric calibration, illumination and color corrections. Synthetic sources are simulated in scientific and super-sky-flat images, with the purpose of estimating completeness and photometric accuracy for the survey. Number counts and color distributions are compared to literature observational and theoretical data, including non-evolutionary, PLE, evolutionary and semi-analytic ΛCDM galaxy models, as well as Milky Way stellar predictions. The ELAIS-S1 area benefits from extensive follow-up from X-ray to radio frequencies: some potential uses of the multi-wavelength observations are illustrated. Results. Object coordinates are defined with an accuracy as good as ∼0.15 [arcsec] rms with respect to GSC 2.2; flux uncertainties are ∼2, 10, 20% at mag. 20, 23, 24 respectively (Vega); we reach 95% completeness at B, V ∼ 25 and R ∼ 24.5. ESIS galaxy number counts are in good agreement with previous works and are best reproduced by evolutionary and hierarchical ΛCDM scenarios. Optical-Spitzer color−color plots promise to be very powerful tools to disentangle different classes of sources (e.g. AGNs, starbursts, quiescent galaxies). Ultraviolet GALEX data are matched to optical and Spitzer samples, leading to a discussion of galaxy properties in the UV-to-24 µm color space. The spectral energy distribution of a few objects, from the X-rays to the far-IR are presented as examples of the multi-wavelength study of galaxy emission components in different spectral domains.

Observations of the long-lived emission--or 'afterglow'--of long-duration gamma-ray bursts place them at cosmological distances, but the origin of these energetic explosions remains a mystery. Observations of optical emission contemporaneous with the burst of gamma-rays should provide insight into the details of the explosion, as well as into the structure of the surrounding environment. One bright optical flash was detected during a burst, but other efforts have produced negative results. Here we report the discovery of the optical counterpart of GRB021004 only 193 seconds after the event. The initial decline is unexpectedly slow and requires varying energy content in the gamma-ray burst blastwave over the course of the first hour. Further analysis of the X-ray and optical afterglow suggests additional energy variations over the first few days.