Using the James Webb Space Telescope, an international team of astronomers has found new galaxies in the Spiderweb protocluster. Their characteristics shed light on the growth of galaxies in these large cosmic clusters, and that gravitational interactions in these dense regions are not as important as previously thought.
Spiderweb protocluster
Astronomers study populations of galaxies and detect their physical characteristics in large-scale structures to better understand how galaxies form and how their environment shapes their clusters. The Spiderweb protocluster is a well-studied object in the early Universe. Its light has traveled over 10 billion years to reach us. It shows us a cluster of galaxies in the process of forming, consisting of more than a hundred known galaxies.
Using the Webb, astronomers are trying to better understand this protocluster and detect new galaxies within it. Infrared light passes more freely through cosmic dust than visible light, which is scattered by the dust. Since Webb can see infrared light very well, scientists have used it to observe regions of the Web that were previously hidden from us by cosmic dust and to find out to what extent this dust obscures them.
Development of galactic structures
“We are observing the development of one of the largest structures in the Universe, a city of galaxies under construction. We know that most galaxies in local galaxy clusters (the largest metropolitan areas of the Universe) are old and not very active, and in this work we are observing these objects during their youth,” explains Jose M. Pérez-Martínez of the Canarias Institute of Astronomy and the University of La Laguna in Spain.
According to him, during the development of a galaxy cluster, their physical properties will also change. Now, for the first time, Webb provides new insight into how such structures form.
Webb allowed the team to probe the hydrogen gas with a powerful diagnostic tracer that cannot be studied with ground-based observations. This allowed the team to detect new, highly obscured galaxies belonging to the cluster and study how much they were obscured. This was done in just 3.5 hours of Webb observations.
Unexpected results
“As expected, we found new members of galaxy clusters, but we were surprised to find more than we expected,” explains Ritm Shimakawa from Waseda University in Japan.
The scientists found that previously known members of galaxies (similar to typical star-forming galaxies such as our Milky Way galaxy) are not as dim or filled with dust as previously expected, which also came as a surprise.
“This can be explained by the fact that the growth of these typical galaxies is not primarily caused by the interaction or merger of galaxies that induce star formation,” adds Helmut Dannerbauer from the Canary Astronomical Institute in Spain.
So now scientists believe that this can be explained by star formation fueled by gas accumulating in different places throughout the large-scale structure of the object.
The new results were obtained using Webb’s NIRCam observations and are presented in two papers published today in the Astrophysical Journal. The team plans to study the new members of the galaxy cluster in more detail and confirm their existence with spectroscopic observations using the Webb.
