The James Webb Telescope produces an unparalleled view of the ghostly light in galaxy clusters

In galaxy clusters, there is a small fraction of stars that wander in intergalactic space because they are pulled by the enormous tidal forces generated between the galaxies in the cluster. The light from these stars is called inner light (ICL) and is very faint. It is less than 1% brighter than the darkest sky we can observe from Earth. This is one of the reasons why images from space are so valuable to analyze.

Infrared wavelengths allow us to probe galaxy clusters in a different way than visible light. Thanks to its efficiency at infrared wavelengths and the clarity of the JWST images, IAC researchers Mireia Montes and Ignacio Trujillo have been able to probe the light within the cluster of SMACS-J0723.3-7327 at an unprecedented level of detail. In fact, images from the JWST of the center of this cluster are twice as deep as previous images obtained by the Hubble Space Telescope.

“In this study, we show the great potential of JWST for very faint object observations,” explains Mireia Montes, first author of the article. “This will allow us to study very distant galaxy clusters, and in much greater detail,” she adds.

In order to analyze this extremely dim “ghost” light, as well as the need for observational ability from the new telescope, the researchers developed new analysis techniques, which improve existing methods. “In this work, we needed to do some additional processing of the JWST images to be able to study the light inside the cluster, as it is a faint, stretchy structure. This was key to avoid biases in our measurements,” says Mireia.

Thanks to the data obtained, the researchers were able to demonstrate the potential of light within the cluster to study and understand the processes involved in the formation of massive structures such as galaxy clusters. “In analyzing this scattered light, we found that the inner parts of the cluster are formed by mergers of massive galaxies, while the outer parts are caused by accretion of galaxies similar to our own Milky Way,” she notes.

But these observations not only provide clues about the formation of galaxy clusters, but also about the properties of a mysterious component of our universe: dark matter. The light-emitting stars within the cluster follow the cluster’s gravitational field, making this light an excellent tracker of the distribution of dark matter in these structures.

“JWST will allow us to characterize the distribution of dark matter in these massive structures with unprecedented accuracy, and shed light on their fundamental nature,” concludes Ignacio Trujillo, second author of the article.

The paper was published in Astrophysical Journal Letters.