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Appendix A: Optical counterparts of compact and diffuse sources

To identify optical counterparts for the compact and diffuse radio sources in the field, we overlaid 608 MHz contours on Isaac Newton Telescope (INT) optical images (Fig. A.1). The images are composites of Wide-Field Camera images taken in the B, V, R and I filters between October 1–8, 2009. The total integration times per filter is ~4000 s. The data were flat-fielded and bias-corrected with IRAF (Tody 1993) and the mscred package (Valdes 1998). The I and R band images were also fringe corrected. We removed cosmic rays and other artefacts by rejecting pixels above 3.0σ_rms.

	Fig. A.1 Optical images from the INT telescope. Contours from 608 MHz are overlaid at [4,8,16,32,64,128,256,512,1024]  × σrms level. Sources are labelled as in Fig. 4.
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Appendix B: Spectral index and curvature errormaps

To evaluate the uncertainties in the pixel-by-pixel spectral index and spectral curvature values, we produced error maps. Values in Figs. B.1 and B.2 represent 1σ uncertainties in the spectral index as resulting from the linear fit of the logarithm of the flux measurements as function of log  frequency.

In the fitting procedure, errors on the flux consisted of 10% absolute flux calibration added in quadrature to the rms noise. Figure B.3 presents the curvature uncertainty, which is the average of the errors in the high and low frequency spectral index fits (these are subtracted to obtain the curvature values).

	Fig. B.1 Spectral index error map corresponding to Fig. 14. Figures are in the same order.
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	Fig. B.2 Spectral index error map corresponding to Fig. 15.
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	Fig. B.3 Spectral curvature error map corresponding to Fig. 16.
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© ESO, 2013