March 2019’s “Monthly Media” is from project lead Associate Professor Cathryn Trott, and showcases how the search for the Epoch of Reionisation (EoR) is affected by the presence of the Milky Way and other galaxies within an observation.

The EoR project is hunting for a weak signal from the early Universe. To detect this signal, parts of the sky that are free from emission from our own galaxy and other nearby galaxies are observed. The effect the Milky Way and other galaxies has on the power spectrum observations can be seen in the below GIF. The power spectrum is the generated diagram on the left of the video, showing the amount of signal power on different size scales on the sky.

Left: The power spectrum image, which breaks the radio observation into its component scale-structures. Right: The visible sky above the telescope for each observation, overlayed with the telescope’s beam pattern.

When the observation passes over bright parts of the sky (e.g., the Galactic Anti-Center at RA = 8 hours – just before the GIF loops), we can see the signal power increase. In the below images, the first shows when the Galactic Anti-Center is far from the primary beam, and the second shows when it is within the primary beam.

Can see the effect of the changed position of the Galactic Anti-Center in the images (right) on the power spectrum (left). The increase of power in the lower power spectrum plot destroys the ability of being able to detect the EoR.

These increases in power destroy an EoR observation, as they obscure the same scale-frequencies the EoR signal is expected to occupy. This information helps to define the observing fields for the EoR experiment and bring its detection closer.