Australia Telescope Search for Cosmic Microwave Background Anisotropy

We have made an 8.7 GHz image of a sky region with a resolution of 8 arcmin and high brightness sensitivity using the Australia Telescope Compact Array (ATCA). in an ultra compact configuration. The foreground discrete-source confusion was estimated from observations with higher resolution at the same frequency and in a scaled array at a lower frequency. Following the subtraction of the foreground confusion, the field shows no features in excess of the instrument noise. This limits the CMB anisotropy flat-band power to Q_flat < 23.6 microK with 95 per cent confidence; the ATCA filter function F_l in multipole l-space peaks at l_eff = 4700 and has half maximum values at l = 3350 and 6050.Comment: Tex, 10 pages with 7 embedded figures, uses mn.tex accepted for publication in MNRA

The properties of extragalactic radio sources selected at 20 GHz

We present some first results on the variability, polarization and general properties of radio sources selected in a blind survey at 20 GHz, the highest frequency at which a sensitive radio survey has been carried out over a large area of sky. Sources with flux densities above 100 mJy in the AT20G Pilot Survey at declination -60 to -70 were observed at up to three epochs during 2002-4, including near-simultaneous measurements at 5, 8 and 18 GHz in 2003. Of the 173 sources detected, 65% are candidate QSOs, BL Lac objects or blazars, 20% galaxies and 15% faint (b > 22 mag) optical objects or blank fields. On a 1-2 year timescale, the general level of variability at 20 GHz appears to be low. For the 108 sources with good-quality measurements in both 2003 and 2004, the median variability index at 20 GHz was 6.9% and only five sources varied by more than 30% in flux density. Most sources in our sample show low levels of linear polarization (typically 1-5%), with a median fractional polarization of 2.3% at 20 GHz. There is a trend for fainter sources to show higher fractional polarization. At least 40% of sources selected at 20GHz have strong spectral curvature over the frequency range 1-20 GHz. We use a radio `two-colour diagram' to characterize the radio spectra of our sample, and confirm that the radio-source population at 20 GHz (which is also the foreground point-source population for CMB anisotropy experiments like WMAP and Planck) cannot be reliably predicted by extrapolating the results of surveys at lower frequencies. As a result, direct selection at 20 GHz appears to be a more efficient way of identifying 90 GHz phase calibrators for ALMA than the currently-proposed technique of extrapolation from all-sky surveys at 1-5 GHz.Comment: 14-page paper plus 5-page data table. Replaced with published versio

The HIPASS Catalogue - II. Completeness, Reliability, and Parameter Accuracy

The HI Parkes All Sky Survey (HIPASS) is a blind extragalactic HI 21-cm emission line survey covering the whole southern sky from declination -90 to +25. The HIPASS catalogue (HICAT), containing 4315 HI-selected galaxies from the region south of declination +2, is presented in Meyer et al. (2004a, Paper I). This paper describes in detail the completeness and reliability of HICAT, which are calculated from the recovery rate of synthetic sources and follow-up observations, respectively. HICAT is found to be 99 per cent complete at a peak flux of 84 mJy and an integrated flux of 9.4 Jy km/s. The overall reliability is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy or integrated flux > 8.2 Jy km/s. Expressions are derived for the uncertainties on the most important HICAT parameters: peak flux, integrated flux, velocity width, and recessional velocity. The errors on HICAT parameters are dominated by the noise in the HIPASS data, rather than by the parametrization procedure.Comment: Accepted for publication in MNRAS. 12 pages, 11 figures. Paper with higher resolution figures can be downloaded from http://hipass.aus-vo.or

The Australia Telescope 20GHz (AT20G) Survey: analysis of the extragalactic source sample

The Australia Telescope 20 GHz (AT20G) survey is a blind survey of the whole Southern sky at 20 GHz with follow-up observations at 4.8, 8.6, and 20 GHz carried out with the Australia Telescope Compact Array (ATCA). In this paper we present an analysis of radio spectral properties in total intensity and polarisation, sizes, optical identifications, and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over the whole Southern sky excluding the strip at Galactic latitude |b|<1.5deg. The sample has a flux density limit of 40 mJy. Completeness has been measured as a function of scan region and flux density. Averaging over the whole survey area the follow-up survey is 78% complete above 50mJy and 93% complete above 100mJy. 3332 sources with declination <-15deg have good quality almost simultaneous observations at 4.8, 8.6, and 20GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources. The fraction of flat-spectrum sources decreases from 81% for 20GHz flux densities S>500mJy, to 60% for S<100mJy. There is also a clear spectral steepening at higher frequencies with the median spectral index decreasing from -0.16 between 4.8 and 8.6GHz to -0.28 between 8.6 and 20GHz. Simultaneous observations in polarisation are available for all the sources at all the frequencies. 768 sources have a good quality detection of polarised flux density at 20GHz; 467 of them were also detected in polarisation at 4.8 and/or at 8.6GHz so that it has been possible to compare the spectral behaviour in total intensity and polarisation. We have found that the polarised fraction increases slightly with frequency and decreases with flux density. Cross matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and gamma-ray bands. Redshift estimates are available for 825 sources.Comment: 15 pages, 16 figures, accepted for publication in MNRA

The Australia Telescope 20 GHz (AT20G) Survey: The Bright Source Sample

The Australia Telescope 20 GHz (AT20G) Survey is a blind survey of the whole Southern sky at 20 GHz (with follow-up observations at 4.8 and 8.6 GHz) carried out with the Australia Telescope Compact Array (ATCA) from 2004 to 2007. The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic (|b|>1.5 deg) radio sources south of dec = -15 deg with S(20 GHz) > 0.50 Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz. In this paper we present an analysis of radio spectral properties in total intensity and polarisation, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index \alpha, assuming S\propto \nu^\alpha, decreases from \alpha_{4.8}^{8.6}=0.11 between 4.8 and 8.6 GHz to \alpha_{8.6}^{20}=-0.16 between 8.6 and 20 GHz), even if the sample is dominated by flat spectra sources (85 per cent of the sample has \alpha_{8.6}^{20}>-0.5). The almost simultaneous spectra in total intensity and polarisation allowed us a comparison of the polarised and total intensity spectra: polarised fraction slightly increases with frequency, but the shapes of the spectra have little correlation. Optical identifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13 respectively for QSO and galaxies.Comment: 34 pages, 19 figures, tables of data included, replaced with version published in MNRA

The Australia Telescope 20 GHz Survey: The Source Catalogue

We present the full source catalogue from the Australia Telescope 20 GHz (AT20G) Survey. The AT20G is a blind radio survey carried out at 20 GHz with the Australia Telescope Compact Array (ATCA) from 2004 to 2008, and covers the whole sky south of declination 0 deg. The AT20G source catalogue presented here is an order of magnitude larger than any previous catalogue of high-frequency radio sources, and includes 5890 sources above a 20 GHz flux-density limit of 40 mJy. All AT20G sources have total intensity and polarisation measured at 20 GHz, and most sources south of declination -15 deg also have near-simultaneous flux-density measurements at 5 and 8 GHz. A total of 1559 sources were detected in polarised total intensity at one or more of the three frequencies. We detect a small but significant population of non-thermal sources that are either undetected or have only weak detections in low-frequency catalogues. We introduce the term Ultra-Inverted Spectrum (UIS) to describe these radio sources, which have a spectral index alpha(5, 20) > +0.7 and which constitute roughly 1.2 per cent of the AT20G sample. The 20 GHz flux densities measured for the strongest AT20G sources are in excellent agreement with the WMAP 5-year source catalogue of Wright et al. (2009), and we find that the WMAP source catalogue is close to complete for sources stronger than 1.5 Jy at 23 GHz.Comment: 21 pages, accepted for publication in MNRA

The Northern HIPASS catalogue - Data presentation, completeness and reliability measures

The Northern HIPASS catalogue (NHICAT) is the northern extension of the HIPASS catalogue, HICAT (Meyer et al. 2004). This extension adds the sky area between the declination range of +2 deg < dec. < +25.5 deg to HICAT's declination range of -90 deg < dec. < +2 deg. HIPASS is a blind HI survey using the Parkes Radio Telescope covering 71% of the sky (including this northern extension) and a heliocentric velocity range of -1,280 km/s to 12,700 km/s . The entire Virgo Cluster region has been observed in the Northern HIPASS. The galaxy catalogue, NHICAT, contains 1002 sources with v_hel > 300 km/s . Sources with -300 km/s < v_hel < 300 km/s were excluded to avoid contamination by Galactic emission. In total, the entire HIPASS survey has found 5317 galaxies identified purely by their HI content. The full galaxy catalogue is publicly-available at .Comment: 12 pages, accepted for publication by MNRA

Multi-frequency Radio Measurements of SN 1987A over 22 Years

We present extensive observations of the radio emission from the remnant of SN 1987A made with the Australia Telescope Compact Array (ATCA), since the first detection of the remnant in 1990. The radio emission has evolved in time providing unique information on the interaction of the supernova shock with the circumstellar medium. We particularly focus on the monitoring observations at 1.4, 2.4, 4.8 and 8.6 GHz, which have been made at intervals of 4-6 weeks. The flux density data show that the remnant brightness is now increasing exponentially, while the radio spectrum is flattening. The current spectral index value of -0.68 represents an 18+/-3% increase over the last 8 years. The exponential trend in the flux is also found in the ATCA imaging observations at 9 GHz, which have been made since 1992, approximately twice a year, as well as in the 843 MHz data set from the Molonglo Observatory Synthesis Telescope from 1987 to March 2007. Comparisons with data at different wavelengths (X-ray, H\alpha) are made. The rich data set that has been assembled in the last 22 years forms a basis for a better understanding of the evolution of the supernova remnant.Comment: 37 pages, 11 figures, accepted by Ap

High resolution 36 GHz imaging of the Supernova Remnant of SN1987A

The aftermath of supernova (SN) 1987A continues to provide spectacular insights into the interaction between a SN blastwave and its circumstellar en- vironment. We here present 36 GHz observations from the Australia Telescope Compact Array of the radio remnant of SN 1987A. These new images, taken in 2008 Apr and 2008 Oct, substantially extend the frequency range of an ongo- ing monitoring and imaging program conducted between 1.4 and 20 GHz. Our 36.2 GHz images have a diffraction-limited angular resolution of 0.3-0.4 arcseconds, which covers the gap between high resolution, low dynamic range VLBI images of the remnant and low resolution, high dynamic range images at frequencies between 1 and 20 GHz. The radio morphology of the remnant at 36 GHz is an elliptical ring with enhanced emission on the eastern and western sides, similar to that seen previously at lower frequencies. Model fits to the data in the Fourier domain show that the emitting region is consistent with a thick inclined torus of mean radius 0.85 arcsec, and a 2008 Oct flux density of 27 +/- 6 mJy at 36.2 GHz. The spectral index for the remnant at this epoch, determined between 1.4 GHz and 36.2 GHz, is -0.83. There is tentative evidence for an unresolved central source with flatter spectral index.Comment: 34 pages, 9 figures in single column manuscript for

The Australia Telescope 20GHz Survey: Hardware, Observing Strategy, and Scanning Survey Catalog

The Australia Telescope 20GHz (AT20G) survey is a large area (2{\pi} sr), sensitive (40mJy), high frequency (20GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. 2010. In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog.Comment: 32 pages, 20 figures, accepted for publication in experimental astronom