Deep observations of the super-CLASS supercluster at 325 MHz with the GMRT: The low-frequency source catalogue

C. J. Riseley, A. M M Scaife, C. A. Hales, I. Harrison, M. Birkinshaw, R. A. Battye, R. J. Beswick, Michael Brown, C. M. Casey, S. C. Chapman, C. Demetroullas, C. L. Hung, N. J. Jackson, T. Muxlow, B. Watson

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We present the results of 325 MHz Giant Metrewave Radio Telescope observations of a supercluster field, known to contain five Abell clusters at redshift z ~ 0.2. We achieve a nominal sensitivity of 34 μJy beam-1 towards the phase centre. We compile a catalogue of 3257 sources with fiux densities in the range 183 μJy-1.5 Jy within the entire ~6.5 deg2 field of view. Subsequently, we use available survey data at other frequencies to derive the spectral index distribution for a sub-sample of these sources, recovering two distinct populations - a dominant population which exhibit spectral index trends typical of steep-spectrumsynchrotron emission, and a smaller population of sources with typically flat or rising spectra. We identify a number of sources with ultrasteep spectra or rising spectra for further analysis, finding two candidate high-redshift radio galaxies and three gigahertz-peaked-spectrum radio sources. Finally, we derive the Euclidean-normalized differential source counts using the catalogue compiled in this work, for sources with flux densities in excess of 223 μJy. Our differential source counts are consistent with both previous observations at this frequency and models of the low-frequency source population. These represent the deepest source counts yet derived at 325MHz. Our source counts exhibit the well-known flattening atmJy flux densities, consistent with an emerging population of star-forming galaxies; we also find marginal evidence of a downturn at flux densities below 308 μJy, a feature so far only seen at 1.4 GHz.

Original languageEnglish
Article numberstw1734
Pages (from-to)917-940
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date19 Jul 2016
Publication statusPublished - 11 Oct 2016


  • Radio continuum: general
  • Surveys


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