Shimwell, T., Röttgering, H., Best, P., Williams, W., Dijkema, T., de Gasperin, F., …Zwart, J. (2017). The LOFAR Two-metre Sky Survey. I. Survey description and preliminary data release. Astronomy & Astrophysics, 598, https://doi.org/10.1051/0004-6361/201629313