August’s Monthly Media comes from Dr Nichole Barry, who’s showcasing the results of using simulated sky images to remove the effects of the Milky Way from MWA data in order to see the Epoch of Reionisation, when the very first stars and galaxies formed.

In order to see the birth of the first galaxies in the Universe, we first have to look beyond our own galaxy, the Milky Way.

The Epoch of Reionisation (EoR) is a time period in the Universe approximately 13 billion years ago, where the forces of gravity slowly collapsed the featureless gas into the first stars and galaxies.

Seeing this time period would give scientists insight into some of the greatest mysteries in astrophysics and cosmology.

However, the magnetic fields in the Milky Way cause a certain type of emission from electrons that spiral around them, known as synchrotron emission.

Synchrotron emission can be detected by radio telescopes in the Murchison Widefield Array (MWA), and this emission can cloud astronomers’ view of the more distant (and earlier) Universe.

Building on work previously reported on in the Monthly Media series, Nichole has removed the effects of the Milky Way’s synchrotron radiation from MWA images in order to look beyond.

Using a map of the synchrotron emission created by Dr. Mike Kriele during his PhD, a model of what the MWA would see was then created by WODEN, a GPU-enabled simulator created by Dr. Jack Line.

Nichole and her colleagues used these simulations to remove the effects of the Milky Way in MWA data.

The Milky Way can be seen at levels the instrument can only barely pick up. Improvements made by Dr. Nichole Barry to Fast Holographic Deconvolution (FHD), a joint project with Astronomy Data and Computing Services (ADACS), has vastly improved the ability of the images to reach these levels.

In the GIF below, the Milky Way is starting to rise above the horizon in the West (what appears to be a vertical stripe on the left edge) in MWA images that were taken specifically to search for the EoR.

You can see the image of the Milky Way appear and disappear in the left-most side lobe, as a vertical blob. If you look closely, you can see the same image appearing and disappearing with it across the entire image, getting fainter and more obscure as you go further to the right. The effect of the Milky Way, even at the very edge of the detection, has a huge impact on the entire image. In the search for the very faint Epoch of Reionisation signal, it needs to be accurately identified and removed. 

Given the location of the Milky Way, in what’s known as a side-lobe, its effects ripple throughout the entire image, making it difficult to find faint signals like that of the EoR.

Thus, it’s crucial to remove the Milky Way in order to glimpse the first galaxies.