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

• Published in: Monthly notices of the Royal Astronomical Society 2016-10, Vol.462 (1), p.917-940
• Main Authors: Riseley, C. J., Scaife, A. M. M., Hales, C. A., Harrison, I., Birkinshaw, M., Battye, R. A., Beswick, R. J., Brown, M. L., Casey, C. M., Chapman, S. C., Demetroullas, C., Hung, C.-L., Jackson, N. J., Muxlow, T., Watson, B.
• Format: Article
• Language: English
• Subjects: Catalogues; Counting; Flux; Flux density; Pollution sources; Populations; Radio frequency; Radio sources (astronomy); Radio telescopes; Red shift; Spectral emissivity; Spectrum analysis; Star & galaxy formation
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw1734

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 flux densities in the range $183\,\mu \rm {Jy}{\rm -}1.5\,\rm {Jy}$ 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-spectrum synchrotron 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 325 MHz. Our source counts exhibit the well-known flattening at mJy 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.