Radio sources in the NCP region with the 21CMA

In particular, for fainter radio sources below ~1 Jy, we find a flattening trend of source counts toward lower frequencies. While the thermal noise (~0.4mJy) is well controlled to below the confusion limit, the dynamical range (~10^4^) and sensitivity of current 21CMA imaging are largely limited by calibration and deconvolution errors, especially the grating lobes of very bright sources, such as 3C061.1, in the NCP field, which result from the regular spacings of the 21CMA.

We note that particular attention should be paid to the extended sources, and their modeling and removal may constitute a large technical challenge for current EoR experiments. Our analysis may serve as a useful guide to the design of next generation low-frequency interferometers like the Square Kilometre Array.