An international team of astronomers has turned a new technique into a group of galaxies and the faint light between them, known as “intragroup light,” to characterize the stars that inhabit them.
Lead author of the study published in MNRAS, Dr Cristina Martínez-Lombilla from UNSW Science’s School of Physics, said: “We know next to nothing about intragroup light.
“The brightest parts of the intragroup light are about 50 times fainter than the darkest night sky on Earth. It is extremely difficult to detect, even with the largest telescopes on Earth or in space.”
Using their sensitive technique, which removes light from all objects except intragroup light, the researchers not only detected the intragroup light, but were able to study and tell the story of the stars that populate it.
“We looked at the properties of intragroup stars – those stars lost between galaxy groups. We looked at the age and abundance of the elements that made them up, and then compared those characteristics to stars that still belong to galaxy groups.” , said Dr. Martínez-Lombilla.
“We found that the intragroup light is younger and less metal-rich than the surrounding galaxies.”
Reconstructing the history of intragroup light
The intragroup light orphan stars were not only “anachronistic” but appeared to have a different origin than their nearest neighbors. The researchers found that the character of the intragroup stars appeared similar to the nebulous “tail” of a more distant galaxy.
Combining these clues allowed the researchers to piece together the story, the story, of the intragroup light and how its stars came together in their own stellar orphanage.
“We believe that these individual stars were removed at some point from their home galaxies and are now floating freely, following the gravity of the group,” said Dr Martínez-Lombilla. “The stripping, called tidal stripping, is caused by the passage of massive satellite galaxies, similar to the Milky Way, that pull stars in their wake.”
This is the first time that the intragroup light of these galaxies has been observed.
“Revealing the amount and origin of intragroup light provides a fossil record of all the interactions a galaxy group has experienced and provides a holistic view of the system’s interaction history,” said Dr Martínez – Lumbar
“Besides, these events happened a long time ago. The galaxies [we’re looking at] they are so far away, that we are observing them as they were 2.5 billion years ago. It’s the time it takes for its light to reach us.”
By observing events from long ago, in galaxies so far away, researchers are providing vital data points to the slow evolution of cosmic events.
Custom image processing procedure
The researchers pioneered a unique technique to achieve this penetrating insight.
“We have developed a custom image processing procedure that allows us to analyze the faintest structures in the Universe,” said Dr. Martínez-Lombilla.
“It follows the standard steps for studying faint structures in astronomical images, which involves 2D modeling and removing all light except that from intragroup light. This includes all bright stars in the images , the intragroup light-obscuring galaxies and a remnant of the continuum emission from the sky.
“What makes our technique different is that it’s completely Python-based, so it’s very modular and easily applicable to different datasets from different telescopes rather than just being useful for these images.
“The most important result is that when studying very faint structures around galaxies, every step of the process counts and any unwanted light should be taken into account and removed. Otherwise, your measurements will be wrong.
The techniques presented in this study are a pilot, encouraging future analyzes of intragroup light, said Dr. Martínez-Lombilla.
“Our main long-term goal is to extend these results to a large sample of galaxy groups. Then we can look at the statistics and find out the typical properties regarding the formation and evolution of intragroup light and these extremely common systems of groups of galaxies
“This is key work to prepare the next generation of deep all-sky studies, such as those to be performed with the Euclid Space Telescope and the LSST with the Vera C. Rubin Observatory.”
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