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.

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We report new observations of Zn II and Cr II absorption lines in 10 damped Lyman α systems (DLAs), mostly at redshift z abs > ∼ 2.5 . By combining these results with those from our earlier survey and other recent data, we construct a sample of 34 measurements (or upper limits) of the Zn abundance relative to hydrogen [Zn/H]; the sample includes more than one third of the total number of DLAs known. The plot of the abundance of Zn as a function of redshift reinforces the two main findings of our previous study. (1) Damped Lyman α systems are mostly metal-poor, at all redshifts sampled; the column density weighted mean for the whole data set is [Zn/H] = −1.13 ± 0.38 (on a logarithmic scale), or approximately 1/13 of solar.(2) There is a large spread, by up to two orders of magnitude, in the metallicities we measure at essentially the same redshifts. We propose that damped Lyman α systems are drawn from a varied population of galaxies of different morphological types and at different stages of chemical evolution, supporting the idea of a protracted epoch of galaxy formation. At redshifts z > ∼ 2 the typical metallicity of the damped Lyman α systems is in agreement with expectations based on the consumption of H I gas implied by the recent measurements of Ω DLA by Storrie-Lombardi et al. (1996a), and with the metal ejection rates in the universe at these epochs deduced by Madau (1996) from the ultraviolet luminosities of high redshift galaxies revealed by deep imaging surveys. There are indications in our data for an increase in the mean metallicity of the damped Lyman α systems from z > 3 to ≈ 2, consistent with the rise in the comoving star formation rate indicated by the relative numbers of U and B drop-outs in the Hubble Deep Field.Although such comparisons are still tentative, it appears that these different avenues

We have observed the black hole candidate X-ray binary GX 339-4 at radio wavelengths before, during and after the 1998 high/soft X-ray state transition.We find that the radio emission from the system is strongly correlated with the hard X-ray emission and is reduced by a factor ≥ 25 during the high/soft state compared to the more usual low/hard state. At the points of state transition we note brief periods of unusually optically-thin radio emission which may correspond to discrete ejection events. We propose that in the low/hard state black hole X-ray binaries produce a quasi-continuous outflow, in the high/soft state this outflow is suppressed, and that state transitions often result in one or more discrete ejection events. Future models for low/hard states, such as ADAF/ADIOS solutions, need to take into account strong outflow of relativistic electrons from the system. We propose that the inferred Comptonising corona and the base of the jet-like outflow are the same thing, based upon the strong correlation between radio and hard X-ray emission in GX 339-4 and other X-ray binaries, and the similarity in inferred location and composition of these two components.

We present the first results of coordinated multi-wavelength observations of the Galactic black hole GX 339−4 in a canonical low-hard state, obtained during its 2004 outburst. XMM-Newton observed the source for 2 revolutions, or approximately 280 ksec; RXTE monitored the source throughout this long stare. The resulting data offer the best view yet obtained of the inner accretion flow geometry in the low-hard state, which is thought to be analogous to the geometry in low-luminosity active galactic nuclei. The XMM-Newton spectra clearly reveal the presence of a cool accretion disk component, and a relativistic Fe K emission line. The results of fits made to both components strongly suggest that a standard thin disk remains at or near to the innermost stable circular orbit, at least in bright phases of the low-hard state. These findings indicate that potential links between the inner disk radius and the onset of a steady compact jet, and the paradigm of a radially-recessed disk in the low-hard state, do not hold universally. The results of our observations can best be explained if a standard thin accretion disk fuels a corona which is closely related to, or consistent with, the base of a compact jet. In a brief examination of archival data, we show that Cygnus X-1 supports this picture of the low/hard state. We discuss our results within the context of disk-jet connections and prevailing models for accretion onto black holes.

Measurements of Zn and Cr abundances in 18 damped Lyman α systems (DLAs) at absorption redshifts z abs = 0.692 − 3.390 (but mostly between z ≃ 2 and 3) show that metals and dust are much less abundant in high redshift galaxies than in the Milky Way today. Typically, [Zn/H] ≃ −1.2; as Zn tracks Fe closely in Galactic stars of all metallicities and is only lightly depleted onto interstellar grains, we conclude that the overall degree of metal enrichment of damped Lyman α galaxies ≈ 13.5 Gyr ago (H 0 = 50 km s −1 Mpc −1 , q 0 = 0.05) was ∼ 1/15 solar.Values of [Cr/Zn] span the range from ≃ 0 to < ∼ − 0.65 which we interpret as evidence for selective depletion of Cr onto dust in some DLAs. On average Cr and other refractory elements are depleted by only a factor of ≈ 2, significantly less than in local interstellar clouds. We propose that this reflects an overall lower abundance of dust-which may be related to the lower metallicities, likely higher temperature of the ISM, and higher supernova rates in these young galaxies-rather than an "exotic" composition of dust grains.Combining a metallicity Z DLA ≃ 1/15Z ⊙ with a dust-to-metals ratio ≈ 1/2 of that in local interstellar clouds, we deduce that the "typical" dust-to-gas ratio in damped Lyman α galaxies is ≈ 1/30 of the Milky Way value. This amount of dust will introduce an extinction at 1500 Å of only A 1500 ≈ 0.1 in the spectra of background QSOs. Similarly, we expect little reddening of the broad spectral energy distribution of the high-z field galaxies now being found routinely by deep imaging surveys. Even such trace amounts of dust, however, can explain the weakness of Lyman α emission from star-forming regions. We stress the approximate nature of such general statements; in reality, the range of metallicities and dust depletions encountered indicates that some sight-lines -3through high-redshift galaxies may be essentially dust-free, while others could suffer detectable extinction.Finally, we show that, despite claims to the contrary, these conclusions are not inconsistent with recent high resolution observations of DLAs with the Keck telescope. We point out that the star-formation histories of high-z galaxies are not necessarily the same as that of the Milky Way and that, if depletions of some elements onto dust are not taken into account correctly, it is possible to misinterpret the clues to early nucleosynthesis provided by non-solar element ratios.

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