This is a fly through of a cosmological simulation that has been converted into what a radio telescope such as ASKAP will see.
We start the movie at low frequency, which means a large distance away (redshifting by the Universes expansion shifts the ~1.4 GHz neutral hydrogen line to lower frequencies). The Declination (y-axis) is the 'up-down' axis on the sky and Right Ascension (x-axis) is the 'left-right' measure on the horizon. The field of view in this telescope is 10 square degrees.
The red dots are galaxies and the broad green distributions are of the cosmic web that lies between the galaxies and clusters of galaxies.
The top left panel is the original particle distribution from the simulation, with red colours indicating a strong signal, and blue a weaker signal.
The top right panel is after smoothing the particles in frequency due to thermal broadening. As gas has a temperature individual atoms will move in random directions which will emit HI at different blue/red-shifted frequencies (giving an overall broadening of the signal in frequency).
The bottom right panel takes these particles and smoothes them in space using the smoothing kernel from the simulation, corrected for the projection map of this radio observation.
The bottom left panel is the final step in creating a mock observation by smoothing the datacube with the actual beam of the telescope (seen as a small black circle in the bottom left). This represents the actual observation that a telescope would see.
Credited to Dr Alan Duffy (ICRAR) and the OWLS team.