A rare trio of merging galaxies called J121/1219+1035 contains three actively feeding radio-bright supermassive black holes, according to a team of American astronomers.
An artist's impression of the rare trio of merging galaxies J121/1219+1035, which host three actively feeding radio-bright supermassive black holes and whose jets illuminate the surrounding gas. Image credit: NSF/AUI/NRAO/P. Vostin.
The J1218/1219+1035 system is located approximately 1.2 billion light years from Earth.
It contains three interacting galaxies, whose central supermassive black holes are actively accreting material and glowing brightly in radio mode.
“Triple active galaxies like this are incredibly rare, and finding one in the process of merging gives us the opportunity to see how massive galaxies and their black holes are fused together,” said Dr Emma Schwartzman, a researcher at the US Naval Research Laboratory.
“Observing that all three black holes in this system are radio bright and actively launching jets, we moved the triple radio active galactic nuclei (AGN) from theory to reality and opened a new window into the life cycle of supermassive black holes.”
Dr. Schwartzman and her colleagues used the NSF Very Large Array (VLA) and Very Long Baseline Array (VLBA) to observe J1218/1219+1035.
The observations revealed compact synchrotron emission radionuclei in each galaxy, confirming that all three host AGNs are fueled by growing black holes.
This makes J1218/1219+1035 the first confirmed triple radio AGN system and only the third known triple AGN system in the nearby Universe.
“The three galaxies in J1218/1219+1035 appeared to be in the process of merging with core separations of approximately 22,000 and 97,000 light-years, forming a dynamically connected group whose tidal patterns trace their mutual interactions,” the astronomers said.
“Such triple systems are a key but rarely observed prediction of hierarchical galaxy evolution, in which large galaxies such as the Milky Way grow by repeatedly colliding and merging with smaller satellites.”
“By capturing three actively feeding black holes in the same merging group, the new observations provide an excellent laboratory for testing how galaxy collisions funnel gas into galactic centers and cause black hole growth.”
J1218/1219+1035 was initially flagged as an unusual system based on mid-infrared data from NASA's Wide-field Infrared Survey Explorer (WISE), which suggested at least two hidden AGNs were lurking in the interacting pair of galaxies.
Subsequent optical spectroscopy confirmed the presence of AGN in one nucleus and revealed a composite signature in another, but left the true nature of the third galaxy unclear, since its emission could also have resulted from star formation or shock waves.
“Only with new ultra-sharp radio images from the VLA—at 3, 10, and 15 GHz—we discovered compact radio nuclei precisely aligned with all three optical galaxies, demonstrating that each contains AGN that is radio-bright and likely producing small jets or outflows,” the researchers say.
“The radio spectra of three nuclei show signatures consistent with non-thermal synchrotron emission from AGN, including two sources with typical steep spectra and a third with an even steeper spectrum that may indicate unresolved reactive activity.”
