Largest Galaxy Group Sample Reveals 12 Billion Years of Cosmic Evolution

The dataset spans roughly 12 billion years, capturing light from some of the universe's earliest galaxies to those just one billion years old. The new catalog, soon to be published in the journal Astronomy and Astrophysics (A&A), contains nearly 1,700 galaxy groups, representing the most extensive and detailed sample of its kind. A striking image of a galaxy cluster over six billion light years away from this study has been featured as the European Space Agency's (ESA) picture of the month.

"We're able to actually observe some of the first galaxies formed in the universe," said Ghassem Gozaliasl of Aalto University, who led the study. "We detected 1,678 galaxy groups or proto-clusters - the largest and deepest sample of galaxy groups ever detected - with the James Webb Space Telescope. With this sample, we can study the evolution of galaxies in groups over the past 12 billion years of cosmic time."

Launched in 2022, the JWST's advanced capabilities have enabled astronomers to observe faint, distant galaxies - some a billion times dimmer than the human eye can detect - revealing the universe as it appeared in its early stages. Given the finite speed of light, this allows scientists to peer billions of years into the past, capturing the growth and evolution of galaxies.

Galaxy groups and clusters are dense cosmic environments containing dark matter, hot gas, and massive central galaxies that often host supermassive black holes. "The complex interactions between these components play a crucial role in shaping the life cycles of galaxies and driving the evolution of the groups and clusters themselves," Gozaliasl explained. "By uncovering a more complete history of these cosmic structures, we can better understand how these processes have influenced the formation and growth of both massive galaxies and the largest structures in the universe."

Galaxies are not uniformly distributed but instead form interconnected clusters within a vast structure known as the cosmic web. These dense regions, linked by filaments of dark matter, contain most of the universe's galaxies. Our Milky Way, for instance, is part of a small galaxy group known as the Local Group, which includes the Andromeda Galaxy and dozens of smaller members.

"Like humans, galaxies come together and make families," Gozaliasl noted. "Groups and clusters are really important, because within them galaxies can interact and merge together, resulting in the transformation of galaxy structure and morphology. Studying these environments also helps us understand the role of dark matter, feedback from supermassive black holes, and the thermal history of the hot gas that fills the space between galaxies."

By examining structures from one billion to 12 billion years ago, astronomers can trace the development of galaxy groups over cosmic time. This long-range perspective reveals how the brightest group galaxies (BGGs) at the centers of clusters form through repeated mergers, providing insights into the broader story of galaxy evolution.

"When we look very deep into the universe, the galaxies have more irregular shapes and are forming many stars. Closer to our time, star formation is what we refer to as 'quenched' - the galaxies have more symmetric structures, like elliptical or spiral galaxies. It's really exciting to see the shapes changing over cosmic time," Gozaliasl added. "We can start to address so many questions about what happened in the universe and how galaxies evolved."

Research Report:Astronomers observe largest ever sample of galaxies up to over 12 billion light years away