RACS-mid shows us what the sky looks like at a radio wavelength of 22 cm, similar to the wavelengths used for GPS. Unlike an optical survey, the vast majority of the bright sources are entire galaxies seen from great distances. At these wavelengths, we detect signals such as jets of emission from supermassive black holes, regions of intense star formation and the shockwaves associated with stellar explosions.
Radio waves are difficult to image because of their long wavelength. Our eyes are designed to detect light with a wavelength of 0.00005 cm, so to make an image using 22 cm radio waves we need a very large telescope! ASKAP combines the signals from 36 antennas spread out in two dimensions over an area about 6 km per side. Making the images above requires mathematical reconstruction using a supercomputer.
Some of the brightest sources in RACS are surrounded by speckles or rays that aren't actually real - these are a bit like the elongated diffraction rays that give nearby stars their characteristic shape in optical images.
The data used to make this image was taken from the first data release published in Duchesne, S.W., Thomson, A.J.M., Pritchard, J, Lenc, E., Moss, V.A., et al. (2023). The Rapid ASKAP Continuum Survey IV: continuum imaging at 1367.5 MHz and the first data release of RACS-mid. Publications of the Astronomical Society of Australia, ??, ????.