In a preview of observations that will be made routinely by the Vera C. Rubin Observatory, astronomers found evidence indicating that a galaxy cluster is merging, a first for a nearby (astronomically speaking) cluster.
PROVIDENCE, R.I. [Brown University] - Using one of the most detailed sets of observations ever of a galaxy cluster 700 million light-years from Earth, astronomers have captured the faint glow of stray stars in the process of being ripped from their home galaxy and absorbed into another. The 'bridge' of diffuse light - spanning roughly a million light years between two galaxies in the cluster Abell 3667 - is the first direct evidence that the two brightest galaxies in the cluster are actively merging.
The findings also imply, the researchers say, that Abell 3667 formed from two smaller clusters, which had themselves merged around a billion years ago.
"This is the first time a feature of this scale and size has been found in a local galaxy cluster," said Anthony Englert, a Ph.D. candidate at Brown University and lead author of a study describing the findings. "We knew that it was possible for a bridge like this to form between two galaxies, but it hadn't been documented anywhere before now. It was a huge surprise that we were able to image such a faint feature."
The new images of Abell 3667 were made using the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile. Englert and two colleagues - Ian Dell'Antonio, a professor of physics at Brown, and Mireia Montes, a research fellow at the Institute of Space Sciences in Barcelona, Spain - stitched together a record-breaking 28 hours of observations taken over a span of years by DECam.
"Because Blanco has been imaging with DECam for the past decade, there is a ton of archival data available," Englert said. "It was just a happy coincidence that so many people had imaged Abell 3667 over the years, and we were able to stack all of those observations together."
That extensive observation time is what made it possible to image the dim light of stray stars within the cluster. This type of diffuse light, known as intracluster light or ICL, offers a treasure trove of information about the history of Abell 3667 and the gravitational dance of the galaxies within it.
