Elizabeth Mahony

Publications (4)4.9 Total impact

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

  Marcella Massardi, Ronald D. Ekers, Tara Murphy, Elizabeth Mahony, Paul J. Hancock, Rajan Chhetri, Gianfranco De Zotti, Elaine M. Sadler, Sarah Burke-Spolaor, Mark Calabretta, [......], Michael J. Kesteven, Katherine Newton-McGee, Chris Phillips, Roberto Ricci, Paul Roberts, Robert J. Sault, Lister Staveley-Smith, Ravi Subrahmanyan, Mark A. Walker, Warwick E. Wilson
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  ABSTRACT: 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) from 2004 to 2008. In this paper we present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| < ).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 per cent complete above 50 mJy and 93 per cent complete above 100 mJy. 3332 sources with declination δ < −15° have good quality almost simultaneous observations at 4.8, 8.6 and 20 GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources, with 69 per cent having spectral index α208.6 > − 0.5 (S∝να). The fraction of flat-spectrum sources decreases from 81 per cent for S20 GHz > 500 mJy to 60 per cent for S20 GHz < 100 mJy. There is also a clear spectral steepening at higher frequencies with the median α decreasing from −0.16 between 4.8 and 8.6 GHz to −0.28 between 8.6 and 20 GHz.Simultaneous observations in polarization are available for all the sources at all the frequencies. 768 sources have a good-quality detection of polarized flux density at 20 GHz; 467 of them were also detected in polarization at 4.8 and/or at 8.6 GHz so that it has been possible to compare the spectral behaviour in total intensity and polarization. We have found that the polarized fraction increases slightly with frequency and decreases with flux density. The spectral indices in total intensity and in polarization are, on average, close to each other, but we also found several sources for which the spectral shape of the polarized emission is substantially different from the spectral shape in total intensity. The correlation between the spectral indices in total intensity and in polarization is weaker for flat-spectrum sources.Cross-matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and γ-ray bands. Redshift estimates are available for 825 sources.
  Monthly Notices of the Royal Astronomical Society 03/2011; 412(1):318 - 330. · 4.90 Impact Factor
• Source

  Available from: Gianfranco De Zotti

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

  Marcella Massardi, Ronald D. Ekers, Tara Murphy, Elizabeth Mahony, Paul J. Hancock, Rajan Chhetri, Gianfranco De Zotti, Elaine M. Sadler, Sarah Burke-Spolaor, Mark Calabretta, [......], Michael J. Kesteven, Katherine Newton-McGee, Chris Phillips, Roberto Ricci, Paul Roberts, Robert J. Sault, Lister Staveley-Smith, Ravi Subrahmanyan, Mark A. Walker, Warwick E. Wilson
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  ABSTRACT: 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 MNRAS
  10/2010;
• Source

  Available from: Gianfranco De Zotti

  Article: The Australia Telescope 20 GHz Survey: The Source Catalogue

  Tara Murphy, Elaine M. Sadler, Ronald D. Ekers, Marcella Massardi, Paul J. Hancock, Elizabeth Mahony, Roberto Ricci, Sarah Burke-Spolaor, Mark Calabretta, Rajan Chhetri, [......], Michael J. Kesteven, Emma Lindley, Katherine Newton-McGee, Chris Phillips, Paul Roberts, Robert J. Sault, Lister Staveley-Smith, Ravi Subrahmanyan, Mark A. Walker, Warwick E. Wilson
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  ABSTRACT: 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 MNRAS
  10/2009;
• Source

  Available from: Carole A. Jackson

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

  Marcella Massardi, Ronald D. Ekers, Tara Murphy, Roberto Ricci, Elaine M. Sadler, Sarah Burke, Gianfranco De Zotti, Philip G. Edwards, Paul J. Hancock, Carole A. Jackson, Michael J. Kesteven, Elizabeth Mahony, Christopher J. Phillips, Lister Staveley-Smith, Ravi Subrahmanyan, Mark A. Walker, Warwick E. Wilson
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  ABSTRACT: 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 MNRAS
  09/2007;