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

In galaxy clusters, there is a fraction of stars that wander through intergalactic space because they are pulled along by tremendous tidal forces generated between the galaxies in the cluster. The light emitted by these stars is called intracluster light (ICL) and is extremely faint. Its brightness is less than 1% of the brightness of the darkest sky we can observe from Earth. This is one of the reasons why images taken from space are very valuable for analyzing it.

Infrared wavelengths allow us to explore galaxy clusters in a different way than with visible light. Thanks to its efficiency at infrared wavelengths and the sharpness of the JWST images, IAC researchers Mireia Montes and Ignacio Trujillo were able to explore the intracluster light of SMACS-J0723.3-7327 with a level of detail without previous. In fact, the JWST images 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 to observe such a faint object,” says Mireia Montes, the first author of the paper. “This will allow us to study much more distant clusters of galaxies and in much greater detail,” she adds.

In order to analyze this extremely faint “ghostly” light, while requiring the observation capacity of the new space telescope, researchers have developed new analysis techniques, which improve on existing methods. “In this work, we needed to perform additional processing on the JWST images to be able to study the intracluster light, since it is a weak and extensive structure. This was essential to avoid bias in our measurements”, explains Mireia .

Thanks to the data obtained, the researchers were able to demonstrate the potential of intracluster light to study and understand the processes that go into the formation of structures as massive as galaxy clusters. “Analyzing this diffuse light, we find that the inner parts of the cluster are formed by a merger of massive galaxies, while the outer parts are due to the accretion of galaxies similar to our Milky Way,” he notes. she.

But these observations not only offer clues to the formation of galaxy clusters, but also to the properties of a mysterious component of our universe: dark matter. The stars that emit intracluster light follow the gravitational field of the cluster, which makes this light an excellent tracer of the distribution of dark matter in these structures.

“The JWST will allow us to characterize the distribution of dark matter in these huge structures with unprecedented precision, and shed light on its fundamental nature,” concludes Ignacio Trujillo, the second author of the paper.

The paper is published in Letters from the Astrophysical Journal.