CMB observations using the SKA

We examine the prospects for observations of CMB anisotropy with the SKA; we discuss the advantages of interferometric SKA imaging, observing strategies, calibration issues and the achievable sensitivity. Although the SKA will probably operate at cm wavelengths, where discrete source confusion dominates the CMB anisotropy, its extreme sensitivity to point sources will make it possible to subtract the source contamination at these wavelengths and thereby image the low surface brightness CMB anisotropies on small angular scales. The SKA, operating at 10-20 GHz, may usefully make high-l observations of the CMB anisotropy spectrum and survey the sky for Sunyaev-Zeldovich decrements.Comment: 4 pages. invited talk presented at the XXVIIth General Assembly of the URSI, 17-24 Aug 2002, Maastricht, The Netherland

ATLBS: the Australia Telescope Low-brightness Survey

We present a radio survey carried out with the Australia Telescope Compact Array. A motivation for the survey was to make a complete inventory of the diffuse emission components as a step towards a study of the cosmic evolution in radio source structure and the contribution from radio-mode feedback on galaxy evolution. The Australia Telescope low-brightness survey (ATLBS) at 1388 MHz covers 8.42 sq deg of the sky in an observing mode designed to yield images with exceptional surface brightness sensitivity and low confusion. The ATLBS radio images, made with 0.08 mJy/beam rms noise and 50" beam, detect a total of 1094 sources with peak flux exceeding 0.4 mJy/beam. The ATLBS source counts were corrected for blending, noise bias, resolution, and primary beam attenuation; the normalized differential source counts are consistent with no upturn down to 0.6 mJy. The percentage integrated polarization Pi_0 was computed after corrections for the polarization bias in integrated polarized intensity; Pi_0 shows an increasing trend with decreasing flux density. Simultaneous visibility measurements made with longer baselines yielded images, with 5" beam, of compact components in sources detected in the survey. The observations provide a measurement of the complexity and diffuse emission associated with mJy and sub-mJy radio sources. 10% of the ATLBS sources have more than half of their flux density in extended emission and the fractional flux in diffuse components does not appear to vary with flux density, although the percentage of sources that have complex structure increases with flux density. The observations are consistent with a transition in the nature of extended radio sources from FR-II radio source morphology, which dominates the mJy population, to FR-I structure at sub-mJy flux density. (Abridged)Comment: 18 pages, 8 figues, 6 tables, accepted for publication in MNRA

Proper Motions of Ionized Gas at the Galactic Center: Evidence for Unbound Orbiting Gas

We present radio continuum observations of the spiral-shaped ionized feature (Sgr A West) within the inner pc of the Galactic center at three epochs spanning 1986 to 1995. The VLA A-configuration was used at $\lambda$2cm (resolution of 0\dasec1$\times$0\dasec2). We detect proper motions of a number of features in the Northern and Eastern Arms of Sgr A West including the ionized gas associated with IRS 13 with V(RA)= 113 \pm 10, V(Dec)=150 \pm15 km/s, IRS 2 with V(RA)= 122 \pm 11, V(Dec)=24 \pm 34 km/s and the Norther Arm V(RA)= 126 \pm 30, V(Dec)=--207 \pm 58 km/s. We also report the detection of features having transverse velocities > 1000 km/s including a head-tail radio structure, the ``Bullet'', $\approx4''$ northwest of Sgr A$^*$ with V(RA)= 722 \pm 156, V(Dec)=832 \pm 203 km/s, exceeding the escape velocity at the Galactic center. The proper motion measurements when combined with previous H92$\alpha$ radio recombination line data suggest an unambiguous direction of the flow of ionized gas orbiting the Galactic center. The measured velocity distribution suggests that the ionized gas in the Northern Arm is not bound to the Galactic center assuming a 2.5 million solar mass of dark matter residing at the Galactic center. This implies that the stellar and ionized gas systems are not dynamically coupled, thus, supporting a picture in which the gas features in the Northern Arm and its extensions are the result of an energetic phenomenon that has externally driven a cloud of gas cloud into the Galactic center.Comment: 11 pages, three figures (one color) and one table. Astrophysical Journal Letters in pres

A meta-analysis of randomized trials of behavioural treatment of depression

Reproduced with permission of the publisher. Copyright © 2008 Cambridge University Press.Background. Depression is a common, disabling condition for which psychological treatments, in particular cognitive behavioural therapies are recommended. Promising results in recent randomized trials have renewed interest in behavioural therapy. This systematic review sought to identify all randomized trials of behavioural therapy for depression, determine the effect of such interventions and examine any moderators of such effect. Method. Randomized trials of behavioural treatments of depression versus controls or other psychotherapies were identified using electronic database searches, previous reviews and reference lists. Data on symptom-level, recovery/ dropout rate and study-level moderators (study quality, number of sessions, severity and level of training) were extracted and analysed using meta-analysis and meta-regression respectively. Results. Seventeen randomized controlled trials including 1109 subjects were included in this meta-analysis. A random-effects meta-analysis of symptom-level post-treatment showed behavioural therapies were superior to controls [standardized mean difference (SMD)-0.70, 95% CI -1.00 to -0.39, k=12, n=459], brief psychotherapy (SMD -0.56, 95% CI -1.0 to -0.12, k=3, n=166), supportive therapy (SMD -0.75, 95% CI -1.37 to -0.14, k=2, n=45) and equal to cognitive behavioural therapy (SMD 0.08, 95% CI -0.14 to 0.30, k=12, n=476). Conclusions. The results in this study indicate behavioural therapy is an effective treatment for depression with outcomes equal to that of the current recommended psychological intervention. Future research needs to address issues of parsimony of such interventions

J06587-5558 -- A Very Unusual Polarised Radio Source

We have found a peculiar radio source in the field of one of the hottest known clusters of galaxies 1E0657-56. It is slightly extended, highly polarised (54% at 8.8GHz) and has a very steep spectrum, with alpha ~ -1 at 1.3 GHz, steepening to ~ -1.5 at 8.8GHz (S \propto nu^alpha). No extragalactic sources are known with such high integrated polarisation, and sources with spectra as steep as this are rare. In this paper, we report the unusual properties of the source J06587-5558 and speculate on its origin and optical identification.Comment: 5 pages, 6 figures, accepted by MNRAS letter