the catalogues, as there may be several optical objects within the radio contours of extended sources.

In order to determine whether or not a source is extended the ratio of total flux to peak flux density ($C=S_{\rm int}/S_{\rm peak}$) was calculated for all sources with a match in either the FIRST, GMRT or WSRT surveys or the 324 MHz VLA survey by @2009AJ....137.4846O (OMK2009). Flux density values from these lower-frequency catalogues are used instead of the 10C catalogue as they have a higher resolution than the 10C catalogue (which has a beam size of 30 arcsec). FIRST, GMRT and OMK2009 all have a synthesised beam of $\approx$5 arcsec, while WSRT has a larger beam of $\approx$10 arcsec. (OM2008 and BI2006 have significantly smaller beam sizes, $\approx$1 arcsec, meaning that values of $C$ from these catalogues cannot be directly compared to the other $C$ values so they are not used in this analysis). FIRST and GMRT cover the whole field while WSRT and OMK2009 only cover part of the field. Those sources with a match in either FIRST or GMRT were classified as extended if either $C_{\rm GMRT}$ or $C_{\rm FIRST} > 1.2$, otherwise they were classified as compact for the 