Astronomers have captured one of the most detailed images yet of a galaxy cluster located 700 million light-years away, revealing the faint glow of stars being pulled away from their original galaxy and being sucked into another galaxy. This faint, diffuse band of light stretches about a million light-years between two galaxies in the Abell 3667 cluster, providing the first clear evidence that the cluster's two brightest galaxies are merging.
The faint glow of individual stars scattered between the two bright galaxies indicates that the two galaxies are actively merging, and that the galaxy clusters surrounding them are also merging. The image was composed of a total of 28 hours of observations with the U.S. Department of Energy's 570-megapixel Dark Energy Camera, which is mounted on the National Science Foundation's Victor M. Blanco 4-meter telescope at Cerro Tololo InterAmerican Observatory. Image source: CTIO/NOIRLab/NSF/AURA
Evidence also suggests that Abell 3667 itself originated from the collision of two smaller star clusters about a billion years ago, the team said.
"This is the first time a feature of this magnitude and size has been discovered in the Local Cluster," said Anthony Englert, a doctoral student at Brown University and lead author of the study. "We knew it was possible for such a bridge to form between two galaxies, but nothing had been documented before. It was a surprise that we were able to image such a faint feature."
The new images were taken using the Dark Energy Camera (DECam) mounted on the Victor M. Blanco Telescope at the Inter-American Observatory in Monte Tololo, Chile. Englert teamed up with Brown University physics professor Ian Dell'Antonio and Mireia Montes, a researcher at the Institute of Space Sciences in Barcelona, to combine 28 hours of DECam observations collected over many years to create the record. Their research was published in The Astrophysical Journal.
“Because Blanco has been imaging with DECam for the past decade, a large amount of archived data has been accumulated,” Englert said. "So many people have imaged Abell 3667 over the years, and it's a lucky coincidence that we were able to stack all these observations together."
It is this long observation time that allows us to image the faint light of wandering stars in the cluster. This diffuse light, known as intracluster light (ICL), provides valuable information about the history of Abell 3667 and the gravitational effects of its inner galaxy.
ICL images taken by Englert and colleagues reveal a special type of galaxy merger occurring in Abell 3667. Typically, Englert said, a merger involving the largest galaxy in a cluster of galaxies, called a brightest cluster, or BCG, occurs gradually because it steals stars from many smaller galaxies around it. But this new study shows that something different is happening in this case. Abell 3667 is actually made up of two galaxy clusters, each with its own BCG, that are now merging together. The ICL bridges discovered by the researchers suggest that the larger BCG is stealing stars from the smaller BCG—an event known as a rapid or aggressive merger. As the two BCGs merge, the smaller galaxies surrounding them also merge, making Abell 3667 the product of two merging galaxy clusters. X-ray and radio frequency observations suggest a rapid merger occurred in Abell 3667, but this is the first optical evidence to support this idea.
In May 2024, the sunset at the Rubin Observatory on Mount Pajun in Chile. Image credit: Olivier Bonin/SLAC National Accelerator Laboratory
The light from within galaxy clusters seen in these new images provides an exciting preview of what's to come when the Vera C. Rubin Observatory becomes fully operational later this year or early next year. The Rubin Telescope will use a telescope twice the size of the Blanco telescope and the largest camera ever built to conduct a 10-year deep scan of the entire Southern Hemisphere sky in a project called the Legacy Survey of Space and Time.
"The Rubin Telescope will be able to image the ICL in a similar way to what we have done before, but it will image every local cluster in the southern hemisphere sky," Englert said. "What we're doing is just a fraction of what the Rubin Telescope can do. It will revolutionize ICL research."
This will be a scientific asset for astronomers and astrophysicists. In addition to revealing the history of galaxy clusters, ICL holds clues to some of the universe's most fundamental mysteries, especially dark matter—the mysterious, invisible substance thought to make up most of the universe's mass.
"The ICL is critical to cosmology," Del Antonio said. "This distribution of light should reflect the distribution of dark matter, so it provides an indirect way to 'see' dark matter."
Seeing the invisible – that’s what a powerful telescope is.
Compiled from /scitechdaily